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Diseases of the Nervous System and the Special Senses

C H A P T E R

Learning Objectives

After studying this chapter, you should be able to

■ Recognize the basic structure and functions of the nervous system and major sensory elements

■ Describe the etiology, signs and symptoms, diagnostic tests, and treatment of different types of headache

■ Compare and contrast different types of headache

■ Describe the etiology, signs and symptoms, diagnostic tests, and treatment of infectious diseases of the nervous system

■ Describe degenerative diseases of the central nervous system, including multiple sclerosis, Parkinson’s disease, and amyotrophic lateral sclerosis

■ Discuss inherited and congenital diseases of the nervous system

■ Describe the effects of trauma on the brain and sensory organs

■ Discuss the etiology, signs and symptoms, diagnostic tests, and treatment of seizure disorders

■ Discuss the etiology, signs and symptoms, diagnostic tests, and treatment of CVA (stroke) or related cerebrovascular disorders

■ Describe the etiology, signs and symptoms, diagnostic tests, and treatment of selected eye and ear diseases

13 Benign brain tumors are not very serious and therefore are not cause for concern.

Fiction:Benign tumors tend to grow and crowd out precious cranial space and, thus, apply pressure or restrict blood flow to particular brain regions. If these benign growths are inoperable or uncontrolled, they will kill the victim. Malignant brain tumors may be lethal, but they may also be surgically removed or re- duced with medication or radia- tion. All brain tumors require at- tention and may be lethal if left untreated. Treatment with surgery, medication, or radiation is most successful for slowly growing, encapsulated tumors.

Fact or Fiction?

Photomicrograph of a neuro- fibrillary tangle. (© O.J. Staats/Custom Medical Stock Photo)

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Human Diseases: A Systemic Approach, Seventh Edition, by Mark Zelman, Ph.D., Elaine Tompary, PharmD, Jill Raymond, Ph.D., Paul Holdaway, MA, and Mary Lou Mulvihill, Ph.D. Published by Prentice Hall. Copyright © 2010 by Pearson Education, Inc.

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Death to a Killer

N ot so long ago, your great-grandparent or grandparent may have suffered from this tragic disease or feared it within his or her community. Your parents’ generation began to break free from the grip of this disease, and for today’s generation

this disease has been nearly eradicated. What is this devastating killer disease? Polio. Polio thrived in the United States and around the world until the 1950s, especially impacting the postwar “baby boom” generation. By 1955, Dr. Jonas Salk and Dr. Albert Sabin had formulated vaccines that put this disease on the shelf. How was that incredible feat accomplished?

Dr. Jonas Salk’s vaccine consisted of inactivated poliovirus in- jected intramuscularly, which stimulated production of antibodies against poliovirus. With the institution of broad-scale immunization programs, cases of polio dropped immediately. Dr. Albert Sabin devel- oped an oral vaccine more convenient to administer, particularly to large groups, and it is extremely effective. The Sabin vaccine is taken orally and stimulates the production of antibodies within the diges- tive system, where the viruses reside. Unlike the Salk vaccine, the Sabin vaccine basically destroys the viruses in the digestive system, thus preventing transmission and eliminating carriers. Many re- searchers believe, however, that the Salk vaccine is the better choice because it employs killed virus and ensures that the vaccine itself will not transmit polio, especially secondarily to compromised pa- tients like those with HIV. In 2000, the Centers for Disease Control and Prevention changed course and recommended only the Salk vac- cine in order to eliminate any exposure from live viruses.

The World Health Organization projects that in the near future polio will be eradicated worldwide. Between 1988 and 1998, polio declined 85% worldwide, and today, polio has been eliminated in the United States and from much of the world. The last case of polio in the United States occurred in 1979. In 2003, only 700 cases of polio were found in the world, and three-fourths of these cases were in Nigeria, India, and Pakistan, where undervaccination has enabled numerous outbreaks to occur. Clearly, it remains important to continue immunization, both locally and globally, to end this devastating disease.

Disease Chronicle

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Dendrites (receptor end)

Cell body

Nucleus

Axon (transmitter end)

Branched terminal ends (release neurotransmitters)

Myelin sheath

Figure 13–1 � Typical neuron.

Structural Organization of the Nervous System

The nervous system monitors the external and in- ternal environment of the body and, along with the endocrine system, controls many of the body’s functions, like breathing rate and alertness.

The basic organization of the nervous system includes two major divisions: the central ner- vous system (CNS) and the peripheral nervous system (PNS). The CNS is composed of the brain and spinal cord. It integrates information and controls the peripheral nervous system. The PNS comprises all those nerves outside the CNS, beginning with the 12 pairs of cranial nerves and 31 pairs of spinal nerves. The nerves carry information to and from the CNS. Nerves consist of motor nerves, which carry informa- tion to muscles and glands, and sensory nerves, which carry sensory information from sense re- ceptors to the CNS.

Certain organs are highly specialized for gathering sensory input; these are called organs of the special senses and include the eyes, ears, and nose. Diseases of the eye and ear will be discussed in this chapter; diseases of the nose were described in Chapter 8.

The basic unit of the nervous system is the neuron, or nerve cell. The neuron consists of a cell body with attached filamentous extensions called dendrites that carry information toward the cell body and a filamentous axon that carries information away from the cell body. A neuron is shown in Figure 13–1 �. Receptors attached to sensory neurons are capable of detecting envi- ronmental changes and transmitting messages to the brain or spinal cord (e.g., touch or pain). Motor neurons convey messages from the cen- tral nervous system out to muscles, causing contraction, or to glands, triggering secretion. The axons of sensory and motor neurons are in- sulated by a lipoprotein covering called myelin that forms a sheath, which insulates and pro- tects the neuron. Deterioration of this sheath decreases the impulse velocity and impairs func- tion. When the myelin degeneration becomes profuse it characteristically causes a misfiring or incomplete impulses as in multiple sclerosis.

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The Brain Three membranous coverings, called the meninges, protect the delicate nerve tissue of both the brain and spinal cord. The innermost covering is the pia mater, the middle layer is the arachnoid, and the toughest, outermost cover- ing is the dura mater. Meningitis is a potentially life-threatening disease caused by an inflamma- tion of these coverings.

The brain has three major anatomical areas: the cerebrum, cerebellum, and brain stem. The largest portion of the brain is the cerebrum, com- prised of two cerebral hemispheres. The cerebral surface is highly convoluted with many eleva- tions (gyrus) and depressions (sulcus). The outer surface of the brain, the cortex, consists of gray matter, where nerve cell bodies are concentrated. The inner area consists mostly of white matter,

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Chapter Thirteen Diseases of the Nervous System and the Special Senses ■ 339

the nerve fiber tracts. Deep within the interior of the white matter are clusters of nerve cell bodies known as basal ganglia, also called basal nuclei, which help control position and subconscious movements. It is the basal ganglia (also gray matter) that are defective in Parkinson’s disease, because they fail to produce sufficient quantities of the neurotransmitter dopamine.

Within the brain are four cavities called ven- tricles, where cerebrospinal fluid (CSF) is formed. These ventricles all interconnect and are contin- uous with the central canal of the spinal cord. CSF is derived from plasma and flows out of the ventricles through small openings to circulate over the brain and spinal cord, forming a wa- tery, protective cushion. CSF is reabsorbed into the venous sinuses of the dura mater, and new fluid is formed. Obstruction of cerebrospinal fluid circulation results in hydrocephalus, a condition commonly called “water on the brain” in the newborn.

The cerebellum controls voluntary move- ments, such as riding a bicycle. The brain stem is called the “vitals center” because it regulates heart and breathing rates. These three major brain areas will be examined as part of the CNS survey along with the spinal cord.

The Spinal Cord The spinal cord is housed within the vertebral column and is continuous with the brain stem (Figure 13–2 �). Numerous tracts of nerve fibers within the spinal cord ascend to and descend from the brain, carrying messages to and from muscles, organs, and glands.

The Autonomic Nervous System One division of the PNS is the autonomic ner- vous system (ANS). This system controls inter- nal functioning of the body. The ANS houses the sympathetic and the parasympathetic nervous systems, which often work antagonistically to each other. The hypothalamus, located within the brain, controls certain activities of the ANS and is known as the center for homeostasis. Home- ostasis is the foundation of all fundamental principles in the study of physiology. The ANS controls arterial blood pressure, heart rate, gas-

trointestinal functions, sweating, temperature regulation, and many other involuntary actions. Whereas some peripheral nerves affect skeletal or voluntary muscle, the ANS acts on smooth or involuntary muscle and cardiac muscle. Dis- eases of the digestive system such as stress ul- cers, regional enteritis, and ulcerative colitis (Chapter 9) are influenced by the ANS. As men- tioned earlier, the overall function of the ner- vous system is to monitor and regulate the vari- ous body systems. This monitoring allows the body to adjust to the surrounding environment both internally and externally, and much of this is done by the ANS.

The Sensory Nervous System Sensations detected by receptors and carried by sensory neurons from specialized organs such as the eye and ear, as well as in skin, muscles, tendons, and internal organs, are transmitted to the central nervous system. The spinal cord receives simple sensations and directs simple reflex responses, as when one touches a hot stove and quickly withdraws the hand. Complex sensory information must travel to specialized parts of the brain. Impulses reaching the brain stem and cerebellum bring about many uncon- scious automatic actions, but sensory informa- tion involving thought processes must reach the highest area of the brain, the cerebral cortex.

The cerebral cortex has specialized areas to receive sensory information from all parts of the body, such as the feet, the hands, and the ab- domen. Visual impulses are transmitted to the posterior part of the brain, whereas olfactory and auditory impulses are received in the lateral parts. Association areas of the brain interpret deeper meaning of the sensations, and many of the sensory messages are integrated and stored as memory. Creative thought becomes possible through use of sensory input.

The Motor Nervous System Just as the cerebral cortex has areas specialized for the reception of sensory information, it also has areas that govern motor activity. The pri- mary motor cortex is the frontal lobe that con- trols discrete movements of skeletal muscles.

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Anterior median fissure

Brain

Spinal cord

Spinal nerves

Spinal nerve

Posterior median sulcus

Anterior gray horn

Posterior gray horn

Lateral horn

Dorsal roots

Dorsal root ganglion

Ventral roots

Arachnoid

Denticulate ligament

Dura mater

Pia mater

Subarachnoid space

Figure 13–2 � The brain, spinal cord, and spinal nerves. An expanded view of the spinal cord is shown.

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Because the nerve fibers cross over in the medulla or spinal cord, stimulation on one side of the cerebral cortex affects particular muscles on the opposite side of the body.

Anterior to the primary motor cortex is the premotor cortex, which controls coordinated movements of muscles. This process is accom- plished by stimulating groups of muscles that work together. The speech area is located here and is usually on the left side, especially in right-handed people. Specialized areas of the brain are shown in Figure 13–3 �.

Diagnostic Procedures for the Nervous System

Neurologic laboratory tests include CSF exami- nation obtained by a lumbar (puncture) spinal tap, as previously described. Angiography al- lows visualization of the cerebral circulation through the injection of radiopaque material.

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Computed tomographic (CT) scans are particu- larly valuable for diagnosing pathologic condi- tions such as tumors, hemorrhages, hematomas, and hydrocephalus. Electromyelography (EMG) is a radiographic process by which the spinal cord and spinal subarachnoid space are viewed and photographed after injection of contrast medium into the lumbar subarachnoid space. Myelography is used to identify spinal lesions caused by trauma or disease, such as amy- otrophic lateral sclerosis (ALS). Electroencephal- ography (EEG) records the electrical activity of the brain (brain waves). It is used to diagnose le- sions or tumors, and seizures, in impaired con- sciousness. Magnetic resonance imaging (MRI) uses magnetic fields in conjunction with a com- puter to view and record tissue characteristics at different planes. MRI is excellent for visualiz- ing brain soft tissue, spinal cord, white matter diseases, tumors, and hemorrhages. Where a disease is idiopathic or without cure, the diag- nosis is directed at relief of symptoms, as in Parkinson’s disease.

Foresight, abstract thinking, judgment

Central sulcus

Equilibrium, muscle tone, coordination

Speech

Hearing

Memory, visual and auditory

association

Pain, temp., touch, pressure, position, body image

Vision

SENSO RY A

R E

MOTOR AREA

Figure 13–3 � Specialized areas of the brain.

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For the eye, ophthalmoscopy is used for rou- tine eye exams that may determine cataracts, when viewing through the slit-lighted feature of the scope. Tonometry procedures are for glau- coma determination. Audio exams with tuning fork and electronic audio signals help discover tone quality and hearing loss. Cochlear im- plants help to restore sounds and a better life for people of all ages.

Diseases of the Nervous System

Common Headache Moderate to severe head pain characterizes the common headache. Tension or inflammation of muscles in the head, eyes, neck, and shoulders may cause the common headache. Other causes include dilation or constriction of cerebral blood vessels, allergies, chemical fumes, extreme tem- peratures, and constipation. Simple unintended actions like coughing and laughter may trigger a headache, as may an intracranial mass of tu- mors or lesions. Nausea, vomiting, and sensitiv- ity to noise and light may accompany the com- mon headache and more severe cases.

Common household treatments are rest and NSAIDs (nonsteroid anti-inflammatory drugs) such as aspirin, ibuprofen (Advil), and ace- tominophen (Tylenol). Resting in a dark, quiet room and applying a cold compress may be ben- eficial for many sufferers, especially if time and space are available. Two of the more intense and episodic forms of headache are the cluster headache and the migraine.

Cluster Headache Cluster headache affects 1 to 4 per 1000 individ- uals, and men, especially middle-aged men, are five times more likely to be affected than women. The cluster headache occurs suddenly, produc- ing severe, sharp, and stabbing pain particularly near one eye or temporal area. The headaches are caused by blood vessel abnormalities and may occur two to three times per day for weeks, or may occur intermittently over a span of 1 to 3 months, subside, and recur months or years later. The pain may develop at any time but usu-

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ally occurs at night and tends to last from 30 minutes to several hours. The pain is so severe that many individuals cannot lie down or be idle and may pace about. In contrast with migraine, however, light intensity, sounds, or strange odors do not elicit nausea or vomiting.

Often there is no family history of cluster headache, although this condition tends to run in families. As of this writing, genetic factors have not been determined. Alcohol and nicotine tend to trigger these painful headaches, along with stress, indigestion of specific foods, and glare. Treatment requires medications like subcutaneous or in- tranasal sumatriptan (Imitrex), and inhalation of 100% oxygen and dihydroergotamine works well, as well as biofeedback and reduction of stress. Er- gotamine tartrate is used as a prophylactic agent given in various modes of delivery.

Migraine Headache Migraine headaches are more common in women than in men and usually begin in the teen years or early twenties. The symptoms are throbbing (moderate) pain on one or both sides of the head plus sensitivity to light and noise or certain odors. Because migraines tend to cause nausea and vomiting, they are referred to as a “sick headache.” Sometimes an aura or premo- nition precedes the migraine onset. Additional symptoms include numbness, dizziness, and vi- sual blurring. The headaches last from a few hours to a few days and may recur once a month or once every few years. A history of the symp- toms helps diagnose migraine. Daily or weekly patient logs of activities, especially timing of mi- graine onset and subsequent events, helps re- duce episodes and the need for medication.

Specific causes have not been identified, al- though there may be a natural abatement in some women when they discontinue birth con- trol pills or attain menopause. The concentra- tion of the neurotransmitter serotonin appears to have a role in the pathogenesis of migraines, and nitric oxide (NO), a vasodilator, may be im- plicated as well. When NO or serotonin are blocked, migraine pain subsides.

One of the most recently discovered causes related to migraine headache is a developmental

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or congenital defect in the heart that occurs as much as 25% of the time in those affected. The normal connection between the two atria in a fetal heart, the foramen ovale, happens to re- main open (at least partially) instead of slapping shut at the time of birth. This fetal remnant is called a patent foramen ovale (PFO). Surgeons found that when this defect was closed in their adult patients, migraine episodes were resolved. Clinical trials are currently scheduled to evalu- ate this new development.

Heredity is now known as a primary factor in the case of migraine. It has been documented that a gene on chromosome 1 contributes to sen- sitivity of sound; on chromosome 5 a gene is rec- ognized as one that allows pulsating headaches and sensitivity to light; and a gene on chromo- some 8 is related to vomiting and nausea.

Bed rest and sleep in a dark, quiet room seems to benefit most migraine sufferers. Drug treatment is aimed at prevention and relief of symptoms. NSAIDs may not provide adequate relief, but prescription drugs like opioids, codeine, and mependine are often effective. Im- itrex, mentioned previously, helps relieve pain and reduce nausea and sensitivities to light and sound. Cardiac medications like beta blockers (Atenolol) or calcium channel blockers (Dilti- azem) help, but the exact mechanism is not fully understood, and tricyclic antidepressants have shown positive results as well.

Infectious Diseases of the Nervous System

Certain pathogenic microorganisms are neu- rotropic in that the virus or bacterium has an affinity for nervous tissue. Pathogens obtain ac- cess to the nervous system by many routes, in- cluding wounds or trauma, and systemic infec- tions entering from the thinner paranasal sinuses or mastoid regions.

Meningitis Meningitis is an acute inflammation of the first two meninges that cover the brain and spinal cord: the pia mater and the arachnoid mater. A

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contagious disease, it usually affects children and young adults and may have serious compli- cations if not diagnosed and treated early.

There are many forms of meningitis, and some are more contagious than others. The most common bacterial causes are Haemophilus influenzae; Neisseria meningitidis, also called meningococcus; and Streptococcus pneumoniae. However, other bacteria, as well as viruses, cause meningitis. Enteroviruses account for most of the cases when the virus is identified; in aseptic meningitis no bacterium is found and thus it usually is considered a viral condition. The infecting organisms can reach the meninges from the middle ear, upper respiratory tract, or frontal sinuses; they can also be carried in the blood from the lungs or other infected sites. Healthy children may be carriers of the bacteria and spread the organisms by sneezing or coughing. Viral or aseptic meningitis is consid- ered the cause in 30% of the cases involving nonimmunized individuals, primarily caused by contracted mumps, and it affects males two to five times more frequently than females. This form is normally a mild case of meningitis that may not require specific treatment. Other cases may be caused by the waning polio viruses and occasionally by herpes simplex, and noninfec- tious cases may result from lymphoma, brain cancer, or leukemia.

In the United States the bacterial cases of meningitis range from 0.6 to 4 per 100,000 indi- viduals, or 1400 to 2800, while viral cases affect about 10 per 100,000 individuals. Causative agent, the geographical region, and accessibility to medical coverage influence prevalence; in ad- dition, some agents become resistant to peni- cillin (S. pneumoniae) and others have been reduced because of the vaccine (Hib) for Haemophilus influenzae type B.

The symptoms of meningitis are high fever, chills, and a severe headache caused by in- creased intracranial pressure. A key symptom is a stiff neck that holds the head rigidly. Move- ment of neck muscles stretches the meninges and increases head pain. Nausea, vomiting, and a rash may also be symptomatic. The high fever often causes delirium and convulsions in chil- dren, and they may lapse into a coma.

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L-1 vertebra

Lumbar puncture needle

Coccyx

Conus medullaris

CSF in lumbar cistern

Dura mater

Sacrum

Extradural “space”

Filum terminale

Sacral hiatus

Skin

Fat

Supraspinous ligament

Interspinous ligament

Figure 13–4 � (A) Lumbar puncture, also known as spinal tap. (B) Section of the vertebral col- umn showing the spinal cord and membranes. A lumbar puncture needle is shown at L3–4 and in the sacral hiatus.

Diagnosis of meningitis is made by performing a lumbar puncture (Figure 13–4 �) or spinal tap, in which a hollow needle is inserted into the spinal canal between vertebrae in the lumbar region. This procedure is possible because the spinal cord terminates at or near the first lumbar verte- bra, although a sac containing cerebrospinal fluid extends down to the sacrum. In addition, a spinal tap may reveal the relative pressure of cerebrospinal fluid. The infected fluid contains an elevated protein level, numerous poly- morphs/leukocytes, and infecting agents. When the level of glucose in the cerebrospinal fluid is below normal, bacteria may have used the sugar for their own growth and metabolism.

The prognosis depends on the cause of meningitis and a prompt diagnosis and treat- ment. Treatment with antibiotics like Rifampin, ciprofloxacin, or ceftriaxone is very effective if the meningitis is bacterial. If not treated, about 15% of those affected suffer permanent brain damage that manifests by sight or hearing loss, paralysis, mental retardation, or death. An- other complication is blockage of the fourth ventricle by a pyogenic (bacteria) infection, which results in the accumulation of cere- brospinal fluid in the brain, a form of hydro- cephalus. Preventive measures include viral vaccines like Hib or MPSV4 (meningococcal polysaccharide vaccine, recommended for ages

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above 2 years) and a conjugate vaccine (MCV4) for ages 11 to 55.

Encephalitis Encephalitis, an inflammation of the brain and meninges, is caused by several types of viruses. Some of these viruses may be harbored by wild birds and transmitted to humans by mosqui- toes, commonly called arborviruses (carried by arthropods-insects). These cases are mostly seasonal and are represented by regional varia- tions that occur within the United States, like Western, California, St. Louis, and Eastern. Along with West Nile, the California and St. Louis varieties of encephalitis seem to dominate in the United States. In 2003, West Nile caused an outbreak of 9800 cases and 250 deaths.

Symptoms of encephalitis range from mild to severe, such as headache, sudden fever, stiff neck, and drowsiness, to more severe cases that include cerebral dysfunction, disordered thought patterns, and seizures in 5% of the cases. Most cases resolve themselves within 1 to 2 weeks with no specific treatment required ex- cept for mild, flu-like symptoms. In serious cases involving extensive brain damage, conva- lescence is slow and requires prolonged physi- cal rehabilitation. Some nerve damage may cause paralysis, as occurs in 10% of these cases. Personality changes or other emotional disturbances may occur that require therapy.

Diagnosis of encephalitis is made by lumbar puncture. Brain imaging CT or MRI may be used to check for brain swelling, and a blood test will determine the presence of West Nile. Treatment is essentially aimed at controlling high fever and intracranial pressure, maintain- ing fluid and electrolyte balance, and carefully monitoring respiratory and kidney function. In individuals generally in good health except for the virus, the prognosis is positive with sup- portive treatment.

There are many forms of the disease, and they may occur in epidemics. Lethargic en- cephalitis, or “sleeping sickness,” is one type of encephalitis characterized by persistent drowsi- ness and delirium that sometimes results in coma. Secondary encephalitis may develop from

viral childhood diseases such as chicken pox, measles, and mumps, or herpes. In the case of herpes simplex encephalitis (HSE), type I is most common, but type II may cause infection in newborns or immunocompromised people like those with HIV or who have received an organ transplant. In the latter case, the patient may be treated with acyclovir or valacyclovir medications.

Prevention depends on control of mosquitoes and deterring contact through use of repellents, clothing, and timing of outdoor activities. Other sources may be unavoidable, but early treat- ment is crucial in order to reduce neurological severity and deficits or death.

Poliomyelitis Poliomyelitis, commonly called polio, is an infec- tious disease of the brain and spinal cord caused by an enterovirus. Motor neurons of the medulla oblongata and pons, which houses the respiratory center, and the spinal cord are pri- marily affected. As a result, muscle tissue is not stimulated; it weakens and finally atrophies. If the respiratory muscles are depressed, then an artificial means of respiration is required.

Symptoms of poliomyelitis are stiff neck, fever, headache, sore throat, and gastrointesti- nal disturbances. When diagnosed and treated early, severe damage to the nervous system and paralysis can be prevented. Those who survive paralytic polio may be left with a limp or need a walking aid such as crutches or a wheelchair. Excessive fatigue, muscular weakness, pain, and other difficulties such as muscle atrophy and scoliosis may occur 20 to 30 years after the onset of the disease. The recurrence of these symptoms is known as postpolio syndrome (PPS). Age seems to be an integral factor, al- though PPS’s exact cause remains unknown. Additional rest seems to offer some necessary relief from PPS symptoms.

In the 1940s and early 1950s, polio was a highly prevalent disease around the world and the United States that crippled or killed thou- sands, primarily children. This devastating dis- ease has nearly been eradicated worldwide through the development of the Salk and Sabin

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vaccines (see the Disease Chronicle at the start of this chapter).

Rabies Rabies is an infectious disease of the brain and spinal cord caused by a virus that is transmitted by secretions (saliva, urine) of an infected ani- mal. Rabies is very rare in the United States due to animal and human vaccines in addition to animal control efforts. However, rabies can be lethal, and numerous pets are not vaccinated as required by local or state laws. Along with urban spread, outbreaks are common especially at seasonal times (summer). Rabies is primarily a disease of warm-blooded animals such as dogs, cats, raccoons, skunks, wolves, foxes, and bats, but it can be transmitted to humans through bites or scratches from a rabid animal that licks its fur or feet. (The virus may be airborne as a

mist from urine in caves and in fecal matter, al- lowing for transfer to fur, feet, or saliva.)

The virus passes from the wound site along peripheral nerves to the spinal cord and brain, where it causes acute encephalomyelitis. The incubation period is long, one month to perhaps a year, depending on the distance of the wound from the brain or degree of breached surface. Bites on the face, neck, and hands are the most serious. The mode of tetanus and rabies trans- mission to the central nervous system is illus- trated in Figure 13–5 �.

Symptoms of rabies include fever, pain, men- tal derangement, rage, convulsions, and paraly- sis. Rabies affects the areas of the brain that control the muscles in the throat required for swallowing and also muscles for breathing. As a result, spasms occur within the throat and voice box, causing a painful paralysis. Because of the inability to swallow or clear the throat ef-

Tetanus bacilli

Bite of rabid animal

Virus

Nerve fiber

Toxin

Bacteria remain in necrotic tissue– toxin travels along nerves

Viruses travel along nerves

Nerve fiber

To central nervous system

CNS

Figure 13–5 � Nerve involvement in tetanus and rabies.

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fectively, the infected animal or human pro- duces a profuse, sticky saliva, and thus tends to “foam” at the mouth. Hydrophobia is an aver- sion to water often linked to rabies. The disease is fatal in humans once it reaches the central nervous system and the symptoms described have developed. However, in 2004 a high school sophomore in Wisconsin, who postponed treat- ment for a month—it took that long for clinical rabies to develop after a bat bite—and then spent two months in intensive care, much of that time in a coma, has survived.

In the case of an animal bite, it is extremely important to know if the animal is rabid, and a detailed investigation of the animal must be made as soon as possible. If rabies is suspected, immunization and globulin injections are started on the infected person. The victim re- ceives repeated injections of an altered virus to stimulate antibody production and an immune serum to provide a substantial passive immu- nity. The severity of rabies explains the critical need for the vaccination of dogs and cats against the disease.

Prevention of rabies is achieved by taking a series of three vaccinations over 28 days. The vaccine is required for field workers and medical associates who work with animals and tissues that may carry the rabies virus.

Shingles (Herpes zoster) Shingles is an acute inflammation of sensory neurons caused by the latency effect of the chicken pox virus, Herpes zoster. It may even be caused by shingles exposure itself without a re- activation of the chicken pox virus, but that sce- nario is less common. Shingles is manifested by pain and a rash characterized by small water blisters surrounded by a red area. The lesions follow a sensory nerve, forming a streak toward the midline of the torso, generally across the shoulder, chest, or trunk area. The rash is usu- ally confined to one side of the body and does not cross the midline. Blisters fade and the le- sions dry up and become encrusted. The en- crusted areas cause severe itching and pain and may result in scaring; this after-effect is called postherpetic neuralgia and is caused by the re- lease of substance P (pain agent). The optic

nerve can be affected, causing severe conjunc- tivitis. If not properly treated, ulcerations can form on the cornea, especially from Zoster ker- atitis, and cause scarring or blindness.

Shingles can develop from exposure to a per- son with shingles in the infectious stage. It may also develop from exposure to chicken pox, which has an incubation period of about 2 weeks. It sometimes accompanies other dis- eases, such as pneumonia or tuberculosis. Shingles may also result from trauma or reac- tion to certain drug injections.

Treatment of shingles is directed toward re- lieving the pain and itchiness. Dry ice pads and lotions such as calamine may provide relief. Glucocorticoids may also be prescribed to sup- press the inflammatory reaction, and antiviral agents like acyclovir (Zovirax) are used. About half a million cases of shingles are reported each year in the United States, according to the National Institutes of Allergy and Infectious Dis- eases, although the incidence is closer to 1 mil- lion and is projected to increase with the aging population. Two-thirds of the cases of shingles occur in those over the age of 50, and one half of the cases in those age 85 or more. Repeat occur- rences are mostly found in immunocompro- mised patients.

Prevention includes immunization against chicken pox. For adults 60 and older, a vaccine called Zostavax prevents onset or reduces severity.

Reye’s Syndrome Reye’s syndrome is a potentially devastating neu- rological illness that sometimes develops in chil- dren after a viral infection. Viruses associated with Reye’s syndrome include Epstein-Barr, in- fluenza B, and varicella, the group which causes chicken pox. Use of aspirin during these infec- tions is associated with Reye’s syndrome. The actual cause of the disease is unknown.

Manifestations of Reye’s syndrome include per- sistent vomiting, often a rash, and lethargy about 1 week after a viral infection. Neurologic dysfunc- tion can progress from confusion to seizures to coma. The encephalopathy includes cerebral swelling with elevated intracranial pressure.

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Management is geared toward lowering in- tracranial pressure and monitoring of vital signs, blood gases, and blood pH. The outcome is very satisfactory when diagnosed and treated early, with a recovery rate of 85% to 90%.

Tetanus Tetanus is an acute infectious disease, com- monly called “lockjaw,” characterized by rigid, contracted muscles that are unable to relax. Tetanus is caused by the tetanus toxin, which is produced by a rodlike tetanus bacillus that lives in the intestines of animals and human beings. The organisms are excreted in the fecal material and persist as spores indefinitely in the soil. The bacilli are prevalent in rural areas and in gar- den soil fertilizer containing manure, especially from horse farms or racetracks. About 45 cases of tetanus occur annually in the United States, but in developing countries neonatal tetanus kills about 250,000 per year and is called “the silent death” because the infants die before the birth is recorded.

A laceration, puncture, or animal bite intro- duces the bacterium deep into the tissues, where it flourishes in the absence of oxygen. Thus, deep wounds with ragged, lacerated tissue cont- aminated with fecal material (manure or conta- minated soils) are the most dangerous type.

Tetanus has an incubation period ranging from 1 week to a few weeks. The toxin travels slowly, so the distance from the wound to the spinal cord is significant. The tetanus toxin (see Figure 13–5) anchors to motor nerve cells and stimulates them, which in turn stimulate mus- cles. Muscles become rigid, and painful spasms and convulsions develop. The jaw muscles are often the first to be affected (hence the name

lockjaw, also called trismus in the clinical set- ting). Because these muscles cannot relax, the mouth clamps tightly closed. The neck is stiff, and swallowing becomes difficult. If the muscles of respiration are affected, asphyxiation occurs. Death can result from even a minor wound if the condition is not treated.

Treatment includes a thorough cleansing of the wound and removal of dead tissue and any foreign substance. Immediate immunization to inactivate the toxin before it reaches the spinal cord is crucial. The type of immunization ad- ministered depends on the patient’s history. If the patient has had no previous immunization, tetanus antitoxin is given. If 5 years have elapsed since the previous tetanus injection, the person receives a booster injection of tetanus toxoid to increase the antitoxin level.

Additional treatment includes the adminis- tration of antibiotics like metronidazole (Flagyl) or penicillin G and erythromycin to prevent sec- ondary infections. Sedatives may be used to de- crease the frequency of convulsions. Oxygen under high pressure is also used because the bacillus is anaerobic; that is, it thrives in the absence of oxygen.

Tetanus may be prevented by adequate im- munization. Tetanus toxoid, which stimulates antibody formation, should be given to infants and small children at prescribed times. This in- oculation may be done in combination with the diphtheria toxoid and pertussis vaccine (the lat- ter prevents whooping cough).

Abscesses of the Brain Pyogenic organisms such as streptococci, staphylococci, ameobae, and E. coli can travel to the brain from other infected areas and cause a

Prevention PLUS! Reye’s Syndrome Reye’s syndrome (RS) appeared in the 1950s and virtually disappeared by the 1980s. It has been suggested that the dis- appearance of RS is related to the recognition of metabolic inborn errors that parallel RS in various clinical manners. Reye’s syndrome may be misdiagnosed because of mitochondrial dysfunction that allows various metabolites to increase (e.g., liver enzymes and ammonia) that cause RS-type symptoms and conditions. However, prescribing acetaminophen in- stead of aspirin will prevent this syndrome.

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brain abscess. Infections of the middle ear, skull bones, or sinuses, including the mastoid, as well as pneumonia and endocarditis are poten- tial sources for brain abscess. Figure 13–6 � shows abscesses of the brain.

The symptoms of brain abscess may be mis- leading, because the symptoms may include fever and headache, which can suggest a tumor. Analysis of cerebrospinal fluid shows increased pressure and the presence of neutrophils and lymphocytes, indicating infection.

Once the diagnosis of a brain abscess has been made, the abscess must be opened surgi- cally and drained, and the patient must be treated with penicillin-like antibiotics. Brain ab- scesses are not as common today in the devel- oped world because most infections are held in check by antibiotics. Prevention may be un- avoidable due to accidental trauma situations, but monitoring current infectious situations helps prevent the spread of any disease.

Degenerative Neural Diseases

Some diseases of the nervous system involve the degeneration of nerves and brain tissue. Abnor- malities in muscle and sensory function often

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result from degeneration of nervous tissue. For example, note that Alzheimer’s disease is also discussed in Chapter 14, although it, too, can be considered a type of neurodegenerative dis- ease. Therefore, the description of Alzheimer’s in this section focuses on the degenerative as- pects of nervous tissue.

Alzheimer’s Disease The most common cause of dementia (a syn- drome of brain abnormalities) in the elderly is Alzheimer’s disease (AD), a progressive degener- ative brain disease. The incidence of AD rises with age, and the prevalence doubles about every 5 years. Those aged 60 to 64 have a preva- lence of at least 1%, while that number rises to 30% to 40% for those individuals older than age 85.

The root cause of Alzheimer’s disease is ge- netic, although most cases seem to appear ran- dom or sporadic. Familial cases, or those linked within families, account for about 5% to 10% of the cases. Chromosomes 1, 10, 12, 14, 19, and 21 have shown genes which affect protein pro- duction for specific enzymes or structural com- ponents within nerve cells. In the neuron, a support scaffolding of microtubules helps the cell maintain its integrity and to be functionally

Osteomyelitis

Brain abscess (caused by osteomyelitis of skull)

Abscesses

Figure 13–6 � Abscesses of the brain.

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sound. The directional protein making these mi- crotubules may be corrupted by a malformed compound known as the tau protein. This cor- ruption causes a malformation of microtubules that normally form the linear feature of a neu- ron and results in a contracted mass known as neurofibrillary tangles. These tangles are not unique to Alzheimer’s disease but do indicate a significant breakdown of functioning. These ele- ments are apparent upon autopsy inspection, which is required to confirm a diagnosis of Alzheimer’s disease.

Although autopsy is the confirming manner for this devastating disease, a combination of clinical assessment, modern imaging methods, and family history can accurately diagnose AD in 80% to 90% of the cases. Within 5 to 10 years of onset, the person tends to become disabled, immobile, and muted; the person usually dies of pneumonia.

Multiple Sclerosis Multiple sclerosis (MS) is a chronic, progressive, degenerative disorder of the central nervous system. It usually affects young adults between the ages of 20 and 40. MS frequency of occur- rence is rare, at about 0.1%, currently afflicts about 400,000 in the United States and 1 mil- lion worldwide.

At first, the disease manifests itself by muscle impairment, beginning with a loss of balance and coordination. Tingling and numbness ensue and are accompanied by a shaking tremor and muscular weakness. Walking is re- duced to a shuffle or use of a cane, and occa- sionally a wheelchair or a more permanent as- sistance is required. Speech becomes difficult, and urinary bladder dysfunction often develops.

Vision may suddenly become impaired, and double vision frequently occurs. Lesions on the optic nerve can lead to blindness. The individual acquires nystagmus, an involuntary, rapid move- ment of the eyeball. Emotional changes are common due to less independence and func- tional control. Signs and symptoms of MS waffle between periods of remission and exacerbation and proceed at different rates as the disease progresses.

The disease is difficult to diagnose in the early stages, as many disorders of the nervous system have similar symptoms. Diagnosis is based on the specific tissue changes that accompany MS.

The degeneration of nervous tissue in MS in- volves the breaking up or erosion of the neu- ronal (myelin) sheath due to chronic inflamma- tion. The nerve tracts do not degenerate in a regular pattern or to the same degree. There- fore, patchy areas of demyelination appear and become sclerotic. A myelin sheath protects the neuron and acts as an insulator to insure the direction and velocity of the nerve impulse transmission. Any degradation of myelin im- pairs nerve conduction. MRI demonstrates plaques of demyelinated nerve fibers.

The disease basically takes one of four poten- tial directions once established: relapsing-re- mitting involves about 85% of those affected, where flare-up episodes of worsening conditions are followed by partial or complete recovery pe- riods; primary-progressive is exhibited by a slow, gradual deterioration at variable rates of speed with minor plateaus of improvement and involves about 10% of patients; secondary- progressive, or progressive-relapsing involves about 5% of patients and is characterized by steadily progressing deterioration and acute re- lapses with or without recovery.

The cause of MS is still uncertain, and al- though it is considered an autoimmune disease, it has been attributed to various viruses or im- munologic reactions to a virus, bacteria, or trauma and heredity. To date, there is no spe- cific treatment for MS that works effectively for long periods. Physical therapy enables the per- son to use the muscles that are controllable. Muscle relaxants help reduce spasticity, and steroids are often helpful. Some success has been found with beta interferon, and exercising in a pool of cold water seems to be beneficial for some individuals. Psychological counseling is advantageous in dealing with the emotional changes brought about by the disease.

Amyotrophic Lateral Sclerosis Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a chronic, terminal neurological disease noted by a progressive loss

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of motor neurons and supportive astocytes. ALS occurs late in life, most commonly in the fifties and sixties, and is slightly more common in men than in women. The prevalence of ALS is 2 to 3 per 100,000, with an incidence of 3 per 100,000 in the United States.

ALS is characterized by disturbances in motility and atrophy of muscles of the hands, forearms, and legs because of degeneration of neurons in the ventral horn of the spinal cord. Also affected are certain cranial nerves, particu- larly the trigeminal (V), facial nerves (VII), and hypoglossal (XI), which impair muscles of the mouth and throat. Swallowing and tongue movements are affected, and speech becomes difficult or impossible.

The cause of amyotrophic lateral sclerosis is not known. ALS is diagnosed by an electromyo- gram (EMG), which shows a reduction in the number of motor units active with muscle con- traction. Motor units are motor neurons and their connection to a host of muscle fibers. Also observed are fasciculations, the spontaneous, uncontrolled discharges of motor neurons seen as irregular twitchings.

ALS requires early education of the patient and the patient’s family so that a proper man- agement system may be provided to anticipate and prevent certain hazards. Specifically, the prevention of upper airway obstruction and pathologic aspiration—drawing of vomitus or mucus into the respiratory tract—is the main focus. Aspiration can occur from weakened res- piratory musculature and ineffective cough. Death usually occurs within 3 to 5 years after onset of symptoms and generally results from pulmonary failure. However, as the renowned British scientist Stephen Hawking attests, sur- vivorship of ALS does vary.

Prevention of ALS is uncertain because 90% of the cases are undetermined as to origin, while 10% have an autosomal dominant gene on chro- mosome 21. Currently, about 20,000 to 30,000 individuals have ALS in the United States.

Parkinson’s Disease Parkinson’s disease (PD) is a degenerative dis- ease that affects muscle control and coordina- tion. PD normally strikes at midlife, about age

45. Approximately 1.5 million people are af- fected in the United States. More men than women are affected, and as the cause of Parkin- son’s disease is still unknown, environmental factors, particularly undetected viruses, are suspected. A very small percent of PD cases are hereditary as either autosomal dominant or re- cessive genes. The resultant cause is related to a loss of a neurotransmitter called dopamine produced in the substantia nigra of the basal nucleus within the core of the brain. Dopamine suppresses undesired movements that skeletal muscles may be instructed to do but are nor- mally held in check or dormant. Therefore, when dopamine is not present, the unre- strained signals call for an uncoordinated, “shakey” tremor.

Symptoms are progressive and include tremor, rigid muscles, and loss of normal re- flexes. The tremors are called “tremors at rest,” meaning they occur while the patient is inactive and subside when the muscles are put into motion. A masklike facial expression is noticed along with faltering gait and mental depression in approximately 10% to 15% of patients.

In the earlier stages, physical therapy and ex- ercise help maintain flexibility, motility, and mental well-being. Relaxation is particularly im- portant for PD patients because stressful situa- tions worsen the condition. Figure 13–7 � sum- marizes possible effects of PD.

Treatment includes the administration of lev- adopamine (L-dopa), a form of dopamine similar to the natural form that passes the blood–brain barrier. The drug does not stop the degenera- tion, but it restores dopamine levels in the brain and reduces symptom severity. Other similar drugs like pergolide (Permex) and carbidopa-lev- odopa (Sinemet) may be used, as well as anti- cholinergic medications like diphenhydramine (Benadryl) for treatment.

In later stages, physical therapy, including heat and massage, helps reduce muscle cramps and relieve tension headaches caused by the rigidity of neck muscles. Psychological support is needed while learning to cope with the dis- ability. In terminal stages, an increased risk for suicide has been noted.

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POSSIBLE EFFECTS OF

PARKINSON’S DISEASE

Difficulty in swallowing

Loss of libido, impotence

Monotone speech

Involuntarily hurried gate

Muscle weakness

Loss of appetite

Pill-rolling tremor

Masklike expression

Visual degeneration

Constipation

Aching back

Leg cramps

Joint rigidity

Headache

Figure 13–7 � Summary of Parkinson’s disease effects.

Deep brain stimulation with electrodes im- planted into the thalamus has become an addi- tional tool for controlling tremors. The patient may turn on/off the implanted pulse generator by passing a magnet over it. The small, pace- maker-like device is implanted under the collar- bone. Normally, a constant trickle of charge is sent to the thalamus in order to interrupt tremor-causing signals, similar to surgical tech- niques that destroy part of the thalamus to limit involuntary movements.

Another treatment suggested is a sort of “brain transplant,” in which dopamine-produc- ing neural tissue from a mouse or pig is im- planted in the brain to replenish the missing dopamine. Most PD patients are unaware of the initial agent(s) that bring about this disor- der, and prevention is not an option in heredi- tary cases. Pesticides are suspected causative agents.

Essential Tremor About 2 million people in the United States have essential tremor. This disorder is often confused with Parkinson’s disease even though it usually becomes symptomatic in adoles- cence. Like PD, essential tremor progresses with the passage of time; at rest the problem abates. Moving or shaking of the head and hands and a halting or quivering voice are characteristic of this condition. There is a fa- milial pattern, but the genetics are not clear. Drugs like beta blockers, known for heart regu- lation; tranquilizers like Valium; and botox in- jections help approximately 40% of the pa- tients, and a noticeable improvement occurs in about 60% of the patients receiving brain im- plant devices. Still, some of those afflicted choose to leave the disease untreated until it interferes with the basic routines of living.

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Prevention is basically uncertain and there may be familial links, but these associations are not clearly identified at this time.

Huntington’s Disease (Huntington’s Chorea) Huntington’s chorea is a progressive degenerative disease of the brain that results in the loss of muscle control. Chorea refers to involuntary and ceaseless, rapid, jerky movements. The dis- ease affects both the mind and body. Physical disabilities include speech loss and a difficulty in swallowing, coupled with involuntary jerking, twisting motions, and muscle spasms. Person- ality changes include carelessness, poor judg- ment, and impaired memory, ultimately deterio- rating to total mental incompetence.

World prevalence is about 5 per 100,000 peo- ple. Huntington’s disease is an inherited dis- ease, but symptoms may not appear until mid- dle age (ages 30 to 50). If either parent has the disease, the children have a 50% chance of in- heriting it because it is an autosomal dominant trait (see Chapter 5 for a discussion of genetic transmission). The responsible gene has been identified on chromosome 4. The abnormality causes the neurotransmitter dopamine to be produced in excess, and insufficiencies of acetylcholine underlie the dementia and abnor- mal muscle activity. To reduce dopamine action, the receptors are blocked by drugs like phe- nothiazines and haloperidol; however, the choline-promoting-type agents have not been as effective. Given its genetic component, preven- tion is not an option. There is no cure for Hunt- ington’s chorea. When desired, carriers can be identified with gene testing. Following onset, death normally occurs 15 to 20 years afterward, with a progressive deterioration.

Convulsions

A convulsion is a sudden, intense series of un- controllabe muscular contractions and relax- ations. Causes of convulsions include accumu- lation of waste products in the blood, such as occurs in uremia, toxemia of pregnancy, drug

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poisoning, or withdrawal from alcohol. Infec- tious diseases of the brain, such as meningitis and encephalitis, and high fevers, especially in young children, are frequently accompanied by convulsions. The basis for convulsions is abnor- mal electrical discharges in the brain, which ab- normally stimulates muscles to contract.

Epilepsy Epilepsy is a group of uncontrolled cerebral dis- charges that recurs at random intervals. The seizures associated with epilepsy are a form of convulsion. Brain impulses are temporarily dis- turbed, with resultant involuntary convulsive movements. Epilepsy can be acquired as a result of injury to the brain, including birth trauma, a penetrating wound, or depressed skull fracture. A tumor can irritate the brain, causing abnormal electrical discharges to be released. Alcoholism can also lead to the development of epilepsy. Most cases of epilepsy are idiopathic, but a pre- disposition to epilepsy may be inherited.

Epilepsy is one of the more common, yet con- trollable, neurological disorders and affects 0.5% to 2% of the U.S. population at an inci- dence rate of about 181,000 per year. Childhood prevalence is rather high, at 4 to 9 per 1000, and involves proportionally more boys than girls.

Epilepsy may manifest itself mildly, particu- larly in children. Loss of consciousness may last only a few seconds, during which time the child appears in a state of shock or absent-mindedness (amnesia). Some muscular twitching may be no- ticed around the eyes and mouth, and the child’s head may sway rhythmically, but the child may not fall to the floor. This form of epileptic seizure is known as absence (or petit mal) and usually disappears by the late teens or early twenties.

Major seizures, called tonic-clonic or grand- mal, involve a sudden loss of consciousness during which the person falls to the floor. Tonic refers to the increased muscle tone or contrac- tion phase, while clonic involves alternating con- tracting and relaxing muscle activities. Absence and tonic forms are considered generalized con- vulsions and range from mild to severe, with vi- olent shaking and thrashing movements lasting about one minute. Hypersalivation causes a

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foaming at the mouth. The individual tends to lose control of the urinary bladder and some- times bowels. Sometimes there are repeated seizures, without a recovery period, that may last 30 minutes. This condition is known as sta- tus epilepticus.

Individuals sometimes have a warning of an approaching seizure that gives them time to lie down or reach for support. This warning, known as an aura, may come as a ringing sound in the ears, a tingling sensation in the fingers, spots before the eyes, or various odors. The signs de- scribed are characteristic of the absence or clonic form of seizure. After a seizure, the per- son is fatigued, groggy, and unaware of what happened. Seizures last for varying lengths of time and appear with varying frequencies.

Epileptic seizures may take different forms. The International Classification of Epileptic Seizures, adopted by the World Health Organi- zation, classifies seizures into four categories:

1. Partial seizures begin locally and may or may not involve a larger area of brain tissue.

2. Generalized seizures are bilaterally sym- metrical and without local onset.

3. Unilateral seizures generally involve only one side of the brain.

4. Unclassified epileptic seizures are less de- fined in origin and degree.

Diagnosis of epilepsy can be made on the re- sults of an electroencephalogram (EEG), a recording of brain waves. X-ray films are also used to identify any brain lesions. Family histo- ries of epilepsy are very important in diagnosing the condition. The diagnosis of epilepsy and the seizure type has become more accurate with new techniques for imaging the brain. CT scans, using x-rays, and MRI, using magnetic fields, vi- sualize brain anatomy.

Medication is very effective in controlling epilepsy, particularly anticonvulsant drugs, such as Dilantin or Tegretol and a more recent medication called Retigabine. Alcohol must be avoided with these types of medication. Molecu- lar neurobiology research is providing new in- formation on how nerve cells control electrical

activity, thus making development of more ef- fective anti-epileptic drugs possible. It is now known which drugs are best for treating the var- ious kinds of seizures. Assistance or treatment during a seizure is directed toward preventing self-injury. Finally, epilepsy does not appear to interfere with mental prowess or creative talents for those afflicted. A consistent medication regi- men usually prevents epileptic episodes.

Developmental Errors or Malformations

Spina Bifida Spina bifida, a neural tube defect (NTD), is a de- velopmental error in which one or more verte- brae fail to fuse, leaving an opening or weak- ness in the vertebral column. The consequences of spina bifida depend on the extent of the opening and the degree to which the vertebral column, usually in the lumbar area, is exposed and the involvement of the spinal cord. One form of spina bifida, spina bifida occulta (hid- den), may not be apparent at birth. In this mildest case, a slight dimpling of the skin and tuft of hair over the vertebral defect indicates the site of the lesion.

Lesions of spina bifida occulta show internal weakness or backbone breaks that can be read- ily seen on x-ray films. Other malformations, such as hydrocephalus, cleft palate, cleft lip, club foot, and strabismus (crossed eyes), tend to accompany this developmental error and may occur simultaneously or separately. Any single malformation may point to spina bifida and trig- ger closer observations of the individual even without noticeable disability. Muscular abnor- malities, such as incorrect posture, inability to walk, or lack of urinary bladder and bowel con- trol, appear later.

A second form of spina bifida noticeable at birth is a meningocele. In this condition, meninges protrude through the opening in the vertebra as a sac filled with cerebrospinal fluid. The spinal cord is not directly involved in this case.

Meningomyelocele is a serious anomaly in which the nerve elements protrude into the sac

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and are trapped, thus preventing proper place- ment and development. The child with this de- fect may be paralyzed, fail to develop, lack sen- sation, and experience mental retardation. The consequences of the defect depend on the region and size of the spinal cord affected. Surgical corrections of the various forms of spina bifida have been very effective. Some procedures are intrauterine, to repair the defect of the fetus, and these new operations look promising. Phys- ical rehabilitation may allow for a more normal lifestyle, depending on severity.

The most severe form of spina bifida is myelocele, in which the neural tube itself fails to close and the nerve tissue is totally exposed and disorganized. This condition is usually fatal. The various forms of spina bifida are shown in Figure 13–8 �.

Hereditary and environmental influences or idiopathic instances are possible causes of spina bifida. Before 1992 the occurrence rate of spina bifida in the United States was 3% to 4% annually, but since the introduction of folate into the neonatal care regimen, that number has been cut in half. Spina bifida and other NTD

cases may be detected by ultrasonagraphy and elevated blood levels of alpha fetoprotein.

Hydrocephalus Hydrocephalus is a consequence of excess CSF trapped within the brain. The formation, circu- lation, and absorption of CSF were described earlier in this chapter. In hydrocephalus, this fluid and pressure increases abnormally, caus- ing the ventricles to enlarge and press the brain against the skull, which forces it to enlarge greatly, especially in the case of newborns.

An obstruction in the normal flow of CSF is the usual cause of hydrocephalus. A congenital defect causes stenosis (narrowing) of an exit opening from the ventricles, or an acquired le- sion can block the CSF flow. Meningitis, a tumor, or birth trauma may result in acquired hydrocephalus. The error may also be a failure to absorb the fluid into the circulatory system.

There are two types of hydrocephalus: communicating and noncommunicating. In the communicating type, the excess CSF enters the subarachnoid space. In the noncommunicating

Nerve fibers

Meninges

Tuft of hair

Dimpling of skin

Cleft in vertebra

Skin

Meninges

Spinal cord

Skin

Spinal cord

Cerebrospinal fluid

Spinal nerves

Spinal cord open- nerve tissue disorganized

Intervertebral disk

Cerebrospinal fluid Cerebrospinal fluid

SPINA BIFIDA OCCULTA MENINGOMYELOCELE

MENINGOCELE MYELOCELE

Figure 13–8 � Forms of spina bifida.

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hydrocephalus, the increased pressure of the CSF is confined within the ventricles and is not evident in a lumbar puncture (LP).

The head of a child born with hydrocephalus may appear normal at birth, but it will enlarge rapidly in the early months of life as the fluid ac- cumulates. The brain is compressed, the cranial bones are thin, and the sutures of the skull tend to separate under the pressure. The appearance of a hydrocephalic infant exhibits a prominent forehead, bulging eyes, and a facial expression of fright or pain. The scalp is stretched, and the veins of the head are prominent. The weight of the excessive fluid in the head makes it impossi- ble for the baby to lift its head. Infant growth is stunted, as is mental development.

There have been cases of self-arrested hydro- cephalus in which expansion of the head stops. A balance is reached between production and absorption of the CSF fluid. The cranial sutures knit together and the skull bones thicken. The extent of brain damage before the arrest deter- mines the degree of mental retardation.

The number of cases involved is difficult to attain due to causes, ages, and matters of de- gree, especially when tabulated in combination with other diseases. For example, an obvious case at birth is noted, but trauma or a tumor or encephalitis cases may not be accounted for and may simply be considered cerebral edema. The incidence of hydrocephalus is approxi- mately 1.8 per 100,000. Success in relieving the excessive CSF has been achieved by placing a shunt between the blocked cerebral ventricles and the jugular vein (Figure 13–9 �), to the heart or placed into the peritoneal cavity. This con- nection facilitates the reduction in cranial pres- sure and allows the fluid to enter the general

circulation. Prevention is difficult due to the un- certainty of events that gradually lead to this crucial disorder.

Brain Injury

Cerebral Palsy Cerebral palsy (CP) is not a disease but a func- tional disorder of the brain manifested by motor impairment that may induce varying degrees of mental retardation and usually becomes appar- ent before age 3. The assault causing brain dam- age may be due to injury at or near the time of birth, a maternal infection such as rubella (Ger- man measles), or infection of the brain even after birth. Reduced levels of oxygen, primarily due to reduced blood flow or incompatible blood type or Rh, may cause brain injury. For example, a pinched umbilical cord against the birth canal may shut off blood and starve the fetus of nec- essary oxygen. With incompatibilities, an Rh-

mother may produce antibodies against the blood of an Rh+ fetus. The result is excessive de- struction of fetal blood cells that causes hyper- bilirubinemia; bilirubin is toxic to the brain and causes damage. Often, cerebral palsy is idio- pathic. Cerebral palsy affects 2 to 4 per 1000 in- fants in the United States and is 10 times more often found in premature and low-weight babies.

There are four recognized forms of cerebral palsy: spastic, choreoathetoid, atactic, and mixed. However, it is not easy to diagnose a spe- cific type before the infant is at least 18 months old because the signs may be subtle and attrib- uted to immature development. The largest per- centage of cerebral palsy type (70%) is the spas-

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Enlarged ventricles

Blocked aqueduct

Catheter tip in ventricle

Valve

Shunt

Figure 13–9 � Hydrocephalus.

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Chapter Thirteen Diseases of the Nervous System and the Special Senses ■ 357

tic version in which muscles are tense and re- flexes are exaggerated. In the athetoid form, constant, purposeless movements are uncon- trollable. A continuous tremor or shaking of the hands and feet is common. Cerebral palsy suf- ferers with the atactic form have poor balance and are prone to fall. Poor muscular coordina- tion and a staggering gait are characteristic of this form of CP.

Depending on the area of the brain affected, there may be seizures along with visual or audi- tory impairment. If the muscles controlling the tongue are affected, speech defects result. Intel- ligence may be normal, but often there is re- duced mental capacity.

Treatment depends on the nature and the severity of the brain injury. Anticonvulsant drugs reduce seizures, and casts or braces may aid walking. In addition, muscle relaxants can relieve spasms along with traction or surgery, which is necessary in some cases. Muscle train- ing is the most important therapy, and the ear- lier it is started, the more effective it is. Preven- tion may depend on circumstances such as sterile environment and strict monitoring of fetal status at the time of birth.

Stroke or Cerebrovascular Accident (CVA)

The main cause of cerebral hemorrhage is hypertension. Prolonged hypertension tends to result from atherosclerosis, which leads to arte- riosclerosis, explained in Chapter 6. The combi- nation of high blood pressure and hard, brittle blood vessels is a predisposing condition for cerebral hemorrhage. Aneurysms, weakened areas in vascular walls, are also susceptible to rupture (Figure 13–10 �). Surrounding the pitu- itary gland is the circle of Willis, a major cross- roads of cerebral vascularity, vulnerable to weakness, especially aneurysms. If the rupture or leakage occurs here, the collection of blood within the cranial cavity mounts, and the in- tracranial pressure increases proportionally to dangerous levels. When this pressure increase is controlled or alleviated early, brain damage and death is unlikely. The pressure relief may come in the form of medication or emergency surgical procedure. Any subsequent hemor- rhage into the brain tissue damages the neu- rons, causing a sudden loss of consciousness.

▼ ▲ Normal ventricles.

SIDE by SIDE ■ Hydrocephalus

▲ Enlarged ventricles in hydrocephalus.

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Aneurysm Anterior cerebral artery (in the anterior communicating artery)

Middle cerebral artery

Circle of Willis

(base of brain) Posterior communicating artery

Posterior cerebral artery

Basilar artery

Figure 13–10 � Aneurysms.

Death can follow, or, if the bleeding stops, vary- ing degrees of brain damage can result. When detected, swift surgical repairs of aneurysms save lives.

Cerebrovascular accident (CVA) is the third lead- ing cause of death in the United States. Preven- tion includes not smoking, maintaining proper diet and exercise, and monitoring blood pres- sure; some people take an 81-mg aspirin each day if they are not taking blood thinners like coumadin. Cerebrovascular accidents are basi- cally of two varieties; those due to a hemorrhage or to a blood clot. Most CVAs result from the blood clot or occlusion and will be addressed in the next section.

Thrombosis and Embolism Blood clots that block the cerebral arteries cause infarction of brain tissue. Thromboses are blood clots that develop on walls of atheroscle- rotic vessels, particularly in the carotid arteries. These clots take time to form, and some warn- ing may precede the occlusion of the vessel. The person may experience blindness in one eye, difficulty in speaking, or a generalized state of confusion. When the cerebral blood vessel is completely blocked, the individual may lose consciousness.

An embolism is a traveling clot that may sud- denly occlude a blood vessel and cause is- chemia. The embolism is most frequently a clot from the heart, aorta, or carotid artery, but it can travel from another part of the body, such

as the deep veins of the leg. Consciousness may be lost suddenly. When this event occurs, tissue plasminogen activator (TPA), called a “clot buster,” may be used to dissolve clots and re- store blood flow in occluded vessels. However, if TPA is given in hemorrhagic cases of cerebro- vascular accidents (CVAs), intracranial bleeding and increasing pressure would continue, and the individual could die. Crucial decisions must be made in acute cases, and because most cere- brovascular accidents are of the ischemic form, TPA is a reliable and available agent for the physician.

The site and extent of the brain damage, re- gardless of its cause, determines the outcome for the patient. Gradually consciousness is re- gained, but immediately after the stroke, speech is often impaired. Loss of speech, or aphasia, is normally temporary but may require therapy to assist in a full recovery.

Damage to the motor nerves at the point passing down the spinal cord causes weakness (paresis) or paralysis on the side of the body op- posite the brain lesion due to the crossover of nerve tracts in the brain stem. Paralysis on one side of the body is referred to as hemiplegia.

Various procedures make it possible to deter- mine the site of blockage in a cerebral blood ves- sel. Angiography, a process in which radiopaque material is injected into cerebral arteries, allows x-rays to locate the lesion.

A blockage in a carotid artery can be treated surgically. Endarterectomy, the more common procedure, removes the thickened area of the

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inner vascular lining. Carotid bypass surgery removes the blocked vascular segment, and a graft is inserted to allow blood flow to the brain. Other vascular replacement may be done in other areas like the inferior aorta to reduce the risk of hemorrhage.

Transient Ischemic Attack Transient ischemic attacks (TIAs) are caused by brief but critical periods of reduced blood flow in a cerebral artery. TIAs may be thought of as “mini” strokes resulting from blood clots occlud- ing vessels or vessel spasms that interrupt blood flow and thus impair neurological functioning. The individual may lose feeling in the face or ex- tremity or have tingling sensations for a brief time. Factors influencing the constrictions are similar to CVA, and with prior TIAs there is a ten-fold chance of a stroke. Reduced flow may be due to an atherosclerotic narrowing of the blood vessel or to small emboli that temporarily lodge in the vessel. The attacks may last less than a minute or two or up to several hours, with the average attack lasting 15 minutes. Manifestations are often abrupt and can include visual disturbances, transient hemiparesis (muscular weakness on one side), or sensory loss on one side. Lips and tongue may become numb, causing slurred speech. Multiple TIAs often precede a complete stroke and may serve as warning of a cerebral vascular disturbance. Further diagnostic testing, such as a cerebral angiogram or CT scan, may be indicated. Pre- vention of a TIA is uncertain, but their occur- rence may alert the person to see a doctor and prevent further damage caused by a full-scale stroke by taking “blood thinning” medications.

Traumatic Disorders

Concussion of the Brain A concussion is a transient disorder of the ner- vous system resulting from a violent blow to the head or a fall. The person typically loses con- sciousness and cannot remember the events of the occurrence. Although the brain may not ac- tually be damaged, the whole body is affected; the pulse rate is weak, and when consciousness

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is regained, the person may experience nausea and dizziness. A severe headache may follow, and the person should be watched closely, since a coma may ensue, and that could be life threatening.

Every year about 1.5 million trauma brain in- juries (TBIs) occur, and concussions, occurring at over 300,000 per year, are a major contribut- ing form. About 50,000 TBI victims die per year, and TBI is a leading cause of death for those under age 45. However, concussions account for only about 1.5 deaths per year in the United States. There are many causes of concussion, from falling, vehicle accidents, and sports in- juries to firearms accidents.

A person suffering from a concussion should be kept quiet, and drugs that stimulate or de- press the nervous system, such as painkillers, are contraindicated. The condition usually cor- rects itself with time and rest. Prevention is difficult because of the unpredictability of some situations, but vehicular accident-related con- cussions are down due to use of seatbelts and child car seats and helmet laws for bicycle riding.

Contusion In a contusion, there is an injury, a bruise, to brain tissue even though the skin at the site of the trauma may not be broken, as it is in a skull fracture. The brain injury may be on the side of the impact or on the opposite side, where the brain is forced against the skull. Blood from bro- ken blood vessels may accumulate in the brain, causing swelling and pain. The blood clots and necrotic tissue form and could block the flow of CFS, causing a form of hydrocephalus.

Efforts must be made to reduce intracranial pressure, and surgery may be necessary to alle- viate pressure and to remove clotted blood areas. Simple pain reduction measures, such as ice packs, may help until professional help ar- rives. Along with observation, rest will be neces- sary for full recovery, although some pain med- ications may be prescribed if needed.

Skull Fractures The most serious complication of a skull frac- ture is damage to the brain. A fracture at the base of the skull is likely to affect vital centers

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Dura

Tearing of emissary vein

Subdural hematoma

Arachnoid

Figure 13–12 � Subdural hematoma.

in the brain stem. The pressure that increases due to accumulation of CSF or blood must be reduced by medications like mannitol. Another danger of skull fractures is that bacteria may be able to directly access the brain.

Hemorrhages Hemorrhages can occur in the meninges, caus- ing blood to accumulate between the brain and the skull. A severe injury to the temple can cause an artery just inside the skull to rupture. The blood then flows between the dura mater and the skull; this is known as an extradural or epidural hemorrhage (Figure 13–11 �). The in- creased pressure of the blood causes the patient to lose consciousness. Surgery is required im- mediately to seal off the bleeding vessel and re- move the blood. No blood would be found in a lumbar puncture because the blood accumula- tion is outside the dura mater.

A hemorrhage under the dura mater, a sub- dural hemorrhage or hematoma (Figure 13–12 �), is a rupture of a cranial vein, or the large ve- nous sinuses of the brain, rather than an artery. This breach may occur from a severe blow to the front or back of the head. The blood clots and CSF accumulates in a cystlike forma- tion. Intracranial pressure increases, but the cerebral symptoms may not develop for a time. Subdural hemorrhages are sometimes chronic occurrences in cases of alcoholic abuse (due to

falling accidents) and in battered or violently abused individuals.

The surface membrane of the brain may be torn by a skull fracture, causing a subarachnoid hemorrhage. Blood flows into the subarach- noid space, where CSF circulates. Blood is found in the CSF with a lumbar puncture. Rupture of an aneurysm can also cause a sub- arachnoid hemorrhage.

Many hemorrhages are accidental and unpre- dictable. Therefore, prevention is not easy to project, but prior symptoms may be used as in- dicators to reduce occurrences.

Brain Tumors

Tumors of the brain may be malignant or be- nign. Because benign tumors may grow and compress vital nerve centers, they are consid- ered serious growths. Benign tumors are usu- ally encapsulated, and they can be completely removed surgically. Malignant tumors have ex- tensive roots and are extremely difficult or im- possible to remove in their entirety. Most malig- nant tumors of the brain are metastatic from other organs, especially the lung and breast.

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Skull fracture

Middle meningeal artery

Epidural hematoma

Edema

Subarachnoid space

Dura

Pia

Rupture

Figure 13–11 � Extradural hematoma.

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Sensory distribution

Ophthalmic division

Maxillary division

Mandibular division

Motor distribution

Figure 13–13 � Sensory and motor distribution of the trigem- inal nerve. There are three sensory divisions: opthalmic, maxil- lary, and mandibular.

Primary malignant tumors of the brain are called gliomas, tumors of the glial cells that sup- port nerve tissue rather than growths of the neurons themselves.

Brain tumors manifest themselves in differ- ent ways depending on the site and growth rate of the tumor. Astrocytomas are basically benign, slow-growing tumors. Glioblastomas multiforma are highly malignant, rapidly growing tumors. Brain function is affected by the increased in- tracranial pressure. Mannitol, corticosteroids, and cranial shunts help relieve those pressure symptoms. Blood supply to an area of the brain may be reduced by an infiltrating tumor or by edema, and that causes dysfunctional activity as well as causing the tissue to become necrotic.

Symptoms of brain tumors typically include a severe headache because of the increased pres- sure of the tumor. Personality changes, loss of memory, or development of poor judgment may give further evidence of a brain tumor. Visual disturbances, double vision, or partial blindness often occur, and the ability to speak may be im- paired. An upright person may be unsteady while standing or become drowsy. Seizures often develop and may progress into a coma.

Diagnostic measures include MRI and CT scans plus a full array of skull x-rays. Treat- ment depends on growth type and location. When possible, surgery (see Chapter 4) is fol- lowed by radiation and/or chemotherapy. Ra- diosurgery uses a gamma knife, and the radia- tion is beamed through designated holes in a helmet that directs the radiation specifically to the target. A limitation of gamma knife surgery is that a special nuclear facility is required for this procedure.

Cranial Nerve Disease

Trigeminal Neuralgia Any one of the twelve pairs of cranial nerves may be subject to impairment. Individual cra- nial nerves may be affected by degeneration or unknown causes and thus involved with vari- ous ailments. The fifth (V) cranial nerve, or trigeminal nerve, may become inflamed, causing severe intermittent pain, usually on one side of

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the face. This condition, known as trigeminal neuralgia or tic doulourex, affects 1 individual per 25,000 (Figure 13–13 �). The cause of tic doulourex is often idiopathic but may be caused by stress, tumors compressing the nerve, or, in young individuals, may be an indication of mul- tiple sclerosis barring other neurological signs. Those affected are usually age 40 or older and complain of severe pain, especially around the oral cavity (the tongue, lips, and gums). This re- curring pain may or may not respond readily to pain medication. Anticonvulsive agents like phenytoin or valproate, and baclofen for muscle spasm, are generally prescribed. In very severe and resistant cases, drugs or agents like alcohol or phenol may be injected directly into the nerve as it exits the skull to reduce the pain, or surgery may be required to cut sensory root ele- ments and give relief in a procedure called rhizotomy.

Bell’s Palsy Bell’s palsy involves the inflammation of the seventh (VII) cranial nerve, or facial nerve. The etiology is usually unknown, but viruses,

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autoimmunity, and vascular ischemia are prob- able factors. This nerve may also be trauma- tized, compressed, or invaded by pathogens. Because the seventh cranial nerve innervates facial muscles and salivary glands, attacks cause sagging of the facial muscles on one side of the face and a watery eye. The person may drool and have slurred speech (Figure 13–14 �). In these cases, massage or heat treatment may help. Recovery may take weeks. The occurrence of Bell’s palsy is about 23 per 100,000 in the United States.

Some corticoid medications like prednisone or antiviral agents (acyclovir) are given if herpes simplex I (HSVI) is suspected. Therefore, relief of symptoms may not always be quick or sim- ple. Bell’s palsy is rare in children. Usually it strikes between ages 25 and 50. If the situation fails to be resolved, a facial contracture devel- ops. The prognosis is generally good, although complete healing may take many months to a year.

Pain

Pain and pain perception are integral parts of nervous system function. In this section, we will discuss the following:

• Definition of pain • The function or purpose of pain • Types and characteristics of pain • The physiology of pain • Pain assessment • Pain management • Other methods of pain control

Pain means different things to different indi- viduals. Pain includes a major degree of percep- tion and therefore is subjective. This symptom requires a level of threshold and therefore acts as a gauge of tolerance, plus learned behaviors, that rely on past experience and culture. Threshold accounts for the initial level of pain that an individual acknowledges, while toler- ance suggests the point at which the same indi- vidual requires treatment in dealing with the pain. Thus, pain may be thought of as an indi- vidualistic occurrence.

In neurophysiology, pain is described as a re- sult of some form of tissue damage. However, this simple definition does not account for emo- tional pain or pain resulting from some func- tional disorders. When physical breakdowns or lesions are apparent, it is easier to ascertain an accompanying pain criterion. Functional dis- parities are not always found or determined through superficial observation (e.g., a micro- scope), but many forms of psychogenic pain are well recognized and treated.

Regardless of definition, perception, or under- standing, pain is a sensation of hurt or a strong discomfort, typically from some form of noxious stimulus. Therefore, pain is caused by injury or disease and transmitted throughout the body to associated cortical areas in the brain for inter- pretation and prospective recourse.

Pain does have a purpose and function. Its primary purpose is to warn the person of an ab- normal state, like inflammation, infection, body trauma, or injury. Second, it is a signal not to

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Figure 13–14 � Bell’s palsy, showing typical drooping of one side of the face. (NIH/Phototake NYC)

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Table 13–1 � Body Regional Pain

Body Region Pain Manifestations

Cranial Headache—common, migraine Oral—toothache, canker sore Facial—Bell’s palsy

Cervical—neck Whiplash—may become chronic pain

Torso Chest—heart pain, lung Abdominal—gastric (e.g., ulcer) Appendix, gallbladder—stones Lumbar—Lower back, pinched nerve Pelvic—ovary, urinary bladder

Extremities— limbs

Muscle and joint pain (e.g., arthritis)

pursue any activity that causes additional pain and thus may cause any more damage. This pause will assist the healing process by allowing the body to rest and conserve resources for re- covery and homeostasis. Pain is considered the most common cause that forces individuals to the doctor’s office or health treatment center.

There is a rare alternative to pain sensation, known as “congenital insensitivity to pain,” found in individuals who are born without a sense of pain. In these cases, the nervous sys- tem is not equipped to instruct the person about injurious conditions or accidents and may allow continual walking on broken limbs or permit advanced infections to go untreated. There is a natural reluctance to pain, but with- out it life may be less safe.

Categories and Characteristics of Pain Various categories of pain usually refer to origi- nation or duration. The pain origin includes areas such as cutaneous (skin), somatic (body), visceral (organ), neuropathic, or referred (redi- rected site). Somatic pain involves blood vessels, nerves, muscles, and joints (e.g., sprained ankle), while cutaneous pain may emanate from a pinprick or sunburn. Visceral pain may be dif- fuse or poorly localized. In the case of appen- dicitis, pain is referred to the surface of the right lower quadrant of the abdomen, even though the problem is internal. (See Table 13–1 �.)

Neuropathic pain may not be caused by a commonly held noxious agent but tends to be delayed and induce a generalized burning sen- sation and occasionally stabbing pain, as found in the legs of some diabetics.

Pain duration is acute (immediate) or chronic. Acute pain has a relatively short time of activity (e.g., within 6 months), whereas chronic pain exceeds the 6-month time frame and may last for years. Severity and specific descriptions, like pounding, throbbing, and sharp or dull, help to qualify the situation as well.

Pain importance may be ascribed to the fact that pain receptors (nociceptors) are the most abundant sensory receptor in the skin; there are as many as 1300 per square inch. Compared to touch or thermal receptors, pain reception is

scattered around to insure basic protection and homeostatic balance. Nociceptors consists of free nerve ending elements (not encapsulated) attached to a sensory neuron. Pain receptors are found in the viscera, or internal organs, as well, as noted by gas pains or gastric burning sensa- tions, and in the muscles and joints.

Physiology of Pain Pain, like other sensations and actions, is inter- preted and delegated to the brain cortex. Differ- ent areas known as cerebral lobes interpret and inform the individual as to various sensations (e.g., sound is interpreted by the temporal lobe). In addition to body location, type and degree of a particular pain stimulus; it is primarily registered in the parietal lobe. In addition, the thalamus, which is known as a major sensory relay center, helps discriminate rudimentary sensations and their location and subsequently relays its input to the respective cerebral lobe. The hypothala- mus responds to coping mechanisms, as does the medulla oblongata. The well-recognized “fight or flight” response induces the adrenal cortex to release corticosteroids for endurance.

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At the same time, the adrenal medulla releases epinephrine to heighten cardiovascular and res- piratory responses in preparation for escape or elevated alertness. These acts of awareness are most valuable when facing fear or major injury and are also coordinated with the brain stem (medulla oblongata and pons), known as the vitals center.

Pain Theory Concept The most commonly supported theory by which pain is exhibited is called the gate control the- ory. It begins with a primary afferent nociceptor complex that has three levels of design and thus influences their role in when, where, and how pain might be dispensed, if at all. The primary differences are in the size or diameter of the neuronal fibers and if they are insulated with myelin or unmyelinated and thus cause a vari- ance in the conduction velocity of their impulse. The largest-diameter fiber type is the A-beta form, which responds to light touch in the skin primarily and therefore normally does not cause a pain response. The small-diameter myelined A-delta and unmyelinated C fibers are found in nerves of the skin and deeper somatic (body) and visceral structures. These fibers are miss- ing in individuals with congenital insensitivity to pain. Some designated areas, like the cornea, have only A-delta and C fiber neurons because they respond maximally only to intense and painful stimuli. For the most part, primary af- ferent nociceptors respond to heat and intense mechanical stimuli (e.g., pinching and noxious or irritating chemicals). When these fibers are blocked from responding, then no pain sensa- tion is expressed.

The gate control theory holds that pain im- pulses are transmitted from specialized nocicep- tors within the skin, muscle, or joints to the spinal cord. These impulses are carried by large A and small C fibers to a specialized area within the superior horn of the spinal cord known as the substantia gelatinosa. This area acts as a gate that regulates transmission for impulses to the CNS. Stimulation of the larger fibers (A) causes cells within substantia gelatinosa to “close the gate” and therefore diminish pain per-

ception. The smaller fiber elements (C) do the re- verse and thus enhance pain perception. De- pending on the degree of opening and closing, the CNS regulates pain output. Similarly, the thalamus, functioning as a relay station, tends to delegate or transmit some pain activity and alter- nately inhibit other pain transmission. The quick-acting myelinated large nerve fibers (A) tend to carry impulses for well-localized, sharp pain, while the unmyelinated C fibers carry sen- sations more slowly, as in a diffuse burning or aching feeling. (See Figure 13–15 �.) Note that amplified or continual outside impulses would interfere with pain input, as when we bang our head against a wall or pound our fist; the force of the activity delays or diverts the pain sensation.

Another concept, known as the nociceptor pain process, extends the gate control theory. It consists of four primary features: transduction, transmission, reception of pain, and modulation; these will be discussed here. These features par- allel physiological nerve conduction operations.

In transduction, the nociceptors distinguish among the various stimuli as to noxious or harmful versus innocuous inputs. Transduc- tion also converts the noxious stimuli into sen- sory nerve ending impulses to the spinal cord and basically describes how pain is perceived by the body. Transmission is the movement of the transduced stimuli into impulses that ascend up the spinal cord to the brain stem and thala- mus. From here the dispatched impulse pro- ceeds to the proper cortical lobe or area (e.g., parietal lobe) for pain interpretation. Some im- pulses may be challenged or blocked from relay as well. Perception of pain means the sensation has become a conscious feeling. The overall per- ception and response process is not well under- stood, especially among different individuals. Again the reminder here is that pain is an indi- vidual-type sensation. Modulation is the manip- ulation that the brain imposes on signals to modify or inhibit pain impulses. In this case, the brain naturally releases compounds that produce relief (analgesia) called endorphins and enkephalins. These compounds are often re- ferred to in the case of marathon runners who feel a sense of euphoria miles into a race. Both of the prevailing concepts of pain attempt to in-

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A Cutaneous nociceptors generate pain impulses

Secondary neuron

Substantia gelatinosa

B Dorsal horn synapses relay impulses up spinal cord

Anterior spinal thalamic tract

Fast pain fibers (to cerebral cortex)

Slow pain fibers (to thalamus)

A-delta (fast pain) fibers

C (slow pain) fibers

C Reticular formation integrates pain response

Figure 13–15 � (A) Cutaneous nociceptors generate pain impulses that travel via A-delta and C fibers to the spinal cord’s dorsal horn. (B) Secondary neurons in dorsal horn pass impulses across spinal cord to anterior spinothalamic tract. C, Slow pain impulses ascend to the thala- mus, while fast pain impulses ascend to the cerebral cortex. The reticular formation in the brainstem integrates the emotional, cognitive, and autonomic responses to pain.

corporate basic neurological processes or prin- ciples with a means to envision a mechanism for interpretation and control.

Pain Assessment and Management The most reliable indicator of the presence and degree of pain is reported by the person experi- encing it. Pain must also be assessed. During the assessment process, there are a variety of considerations: language barriers, children and developmental stage, and those with hearing limitations or who are intubated. A variety of tools are used to assess pain. These tools in- clude simple pictorial or numeric scales or

mnemonics that can help convey vital informa- tion from the patient to the healthcare assistant or clinician (Figure 13–16 �). Culture, age, and past experience with pain can also influence as- sessment findings.

Chronic pain causes fatigue and interferes with the routines of working, eating, sleeping, and concentrating. In the case of cancer, chronic pain may become the central concern. The cancer may become secondary to pain for some stricken individuals, because it may be exacerbated by treatment and fear. Cancer-re- lated pain can be acute or chronic, but accurate assessment of pain is essential as it influences treatment. Counseling and group therapy may

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0 1 2 3 4 5 6 7 8 9 10

No pain Moderate pain

Worst possible

pain

No pain Mild pain

Moderate pain

Severe pain

Worst possible

pain

No pain Pain as bad as it could possibly be

Visual analog scale (VAS)

0–10 Numeric pain intensity scale

Very severe pain

Simple descriptive pain intensity scale

Figure 13–16 � Examples of commonly used pain scales.

help relieve some anxiety and uncertainty, espe- cially in cases of little or no family support.

Pain management depends on a number of variables, but the focus is to control pain with- out serious side effects. Over-the-counter (OTC) drugs and prescription forms such as opiates are often needed to treat acute or chronic pain. See Table 13–2 � for a summary of alternative treatments.

The body has its own endogenous opioid agents, called endorphins or enkephalins, to counteract pain-causing symptoms such as in- duced by substance P, an agent that is thought to be released from a pain source. However, it is the OTC and prescription medications that tend to act on a specific target. Aspirin is a widely used drug; others include NSAIDs, like aceta- minophen (Tylenol), ibuprofen (Advil), or naproxsyn (Aleve), all of which work to reduce or stop pain primarily in the PNS. Opiates or narcotic-type drugs work best in the CNS by blocking or interfering with pain receptors or pathways (e.g., OxyContin or Roxicet). Chronic pain requires stronger remedies like morphine for surgical wounds and Demerol for birth labor or persistent headache. The drug Fentanyl is currently considered the best agent to fight

chronic pain, but because it depresses the res- piratory system, its use is closely monitored.

Diseases of Special Senses: Eye and Ear

Special senses include the nose for olfaction or sense of smell; the tongue for gustatory or taste sensations; the eyes for vision; and the ears for acoustics or hearing. Diseases related to the nose and nasal cavity were discussed in Chapter 8; diseases of the eye and ear are cov- ered in the sections that follow.

The Eye Our discussion starts with protective coverings of the eye, called eyelids and associate glands, and continues to the eye surface or conjunctiva; the clear area known as the cornea; the photorecep- tors and the retina; and the optic nerve (Figure 13–17 �). The ear disorders will also be covered from the external to internal components.

Eyelids and Associate Glands One of the most no- ticeable lesions found on the eyelid is the com- mon stye or hordeolum. This reddish tender lump is caused by a local staphylococcus abscess on the upper or lower lid. Smaller styes tend to be external to the lid surface and on the margin, while internal styes tend to jut toward the eye surface. Sometimes they resolve themselves, but when the lesion is large enough to cause irrita- tion or a reduced field of vision, treatment is re- quired. A warm compress or application of baci- tracin ointment usually resolves the situation. Because of oversight or lack of attention, these common bumps tend to recur, especially in youngsters.

Similar to the stye is a hardened internal le- sion called a chalazion. This inflammation im- pacts a deeper oil gland (meibomian) and feels tender and irritated. The oil secreted by the mei- bomian gland is necessary to prevent the watery tear fluid from evaporating. When the oil is ab- sent, a dry eye develops, which causes pain and potential for a coarse scleral and corneal sur-

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Table 13–2 � Alternative Pain Therapies

Therapy Methodology

Acupuncture Ancient Eastern method may stimulate release of endorphins

Aromatherapy Oils and scents along with bath or massage

Biofeedback therapy Electrothermal devices plus training for pain (e.g., migraine)

Heat and cold packs Traumas such as sprains and burns

Humor Acts as a distraction and comfort, at least temporarily

Hypnosis Extends pain relief or blocks pain perception

Imagery Induces relaxation; may induce endorphins and reduce stress

Massage Promotes muscle relaxation and blood flow for comfort

Music and art Provide soothing atmosphere in clinics and help to calm patient fears

Relaxation techniques Reduce muscle tension and increase pain threshold; reflexology is an example

Transcutaneous electrical nerve stimulation (TENS)

Electrical stimulation through skin patches to interfere with pain release and timing activities

Transcendental meditation (TM) Solitary introspection for calming relaxation

Yoga Body manipulation, mind relaxation, and mind control technique

A B

Vitreous humor

Ciliary body

Suspensory ligament

Lens

Iris

Pupil

Cornea

Anterior cavity

Canal of Schlemm

Central artery and vein of the retina

Optic nerve

Optic disc (blind spot) Fovea centralis Macula

Retina Choroid Sclera

Anterior chamber Posterior chamber

Posterior cavity

Uvea

Figure 13–17 � (A) Human eye anatomy and (B) normal vision image. (National Eye Institute)

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Figure 13–18 � Conjunctivitis. (©Dorling Kindersley)

face or superficial cracks. As in cases of exoph- thalmia, found in Graves’ disease (Chapter 12), eye drops like Restasis (cyclosporine in a castor oil base) help relieve the dryness. When given extended, albeit untreated, time, the condition may resolve itself, but hot compresses normally help, with a gentle message, repeated twice daily for best results. If the condition does not improve, vision may be impaired and a corticos- teroid injection may be needed or the cyst may need to be lanced to let it drain. Once resolved, the problem seems to subside, and with in- creased awareness the occurrence is reduced.

Blepharitis is a common chronic inflammation, with or without ulcers, often involving both eyelid margins and perhaps becoming bilateral (occur- ing in both eyes). This bacterially initiated prob- lem resembles seborrhea of the scalp and eye- brows or perhaps acne rosacea (see Chapter 16). Itching and burning sensations are due to oozing pus, and a thick crust develops, especially after sleep. The potential for ulceration of the cornea is serious, and treatment is warranted. Antibiotic ointment like bacitracin plus polymixin B or sul- facetamide may be used for known microbe types, and if other skin conditions are factors, they should be addressed as well. Preventive measures include good hygiene, with consis- tency, and proper training to keep hands away from nose, mouth, and especially eyes.

Dacryocystitis is an infection and obstruction of the nasolacrimal apparatus for tear produc- tion and drainage. Common skin flora like Staphylococcus aureus or the beta version of streptococcus and yeast infection (e.g., Candida albicans) are all potential sources. Symptoms include swelling, tenderness, and pain. If chronic, tearing and pus discharge are cause for surgical relief, and antibiotics may continue, al- though they may have been unable to dry up the ducting network initially. Spontaneous healing can occur in some patients.

Prevention of common infectious conditions is achieved through hygiene and retraining of old habits, like unnecessary finger and hand contact with the eye. If known allergies are recognized, they must be avoided or eliminated if possible.

Conjunctivitis Conjunctivitis is an inflammation of the conjunctiva, the superficial covering of the

visible sclera (white of the eye) and the inner lin- ings of the eyelids. Red, swollen eyes with dis- charge and some discomfort are the usual symp- toms. About 30% of all eye complaints are for conjunctivitis, commonly called “pink eye,” yet many cases go unreported, and children are the primary source group.

Various fumes, such as from peeled onions or bathroom cleansers, may initiate an inflamma- tory or basically allergic response. However, viruses and various bacteria, including the nor- mal bacterial flora such as Staphylococcus au- reus, or fungi commonly cause conjunctivitis. Unfortunately, these viral and bacterial infec- tions are quite contagious, and therefore pa- tients, usually children, are instructed to stay home from school or social activities. Reinfec- tions may occur due to lack of hygiene and to rubbing or touching the eye unnecessarily. Often the inflammation subsides on its own ac- cord, but it may progress into inclusion conjunc- tivitis, which is caused by particular bacteria (e.g., Chlamydia trachomatis) and is longer last- ing. For diagnosis and determination of infective agents, ocular swabs or scrapings are taken to culture and suggest favorable antidotes. Topical antibiotics or eye drops, such as sulfonamides (even in viral cases, to prevent secondary infec- tion) or antihistamines and cold compresses help control the “pink eye.” See Figure 13–18 �.

Chronic conjunctivitis, or trachoma, results when the infecting agent invades the conjunc-

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Figure 13–19 � Glaucoma visual image reveals tunnel vision. (National Eye Institute)

tiva. These cases tend to be highly contagious and when severe may disrupt the corneal sur- face and impair vision. The infective agent in this case is Chlamydia trachomatis, mentioned previously, the same organism responsible for the STD chlamydia (chapter 11). Infected moth- ers pass on this infection to the newborn. An erythromycin ointment or tetracycline is usually administered to resolve trachoma.

Prevention of conjunctivitis is best achieved by reducing hand to eye contact, disposing of contaminated materials such as contact lenses and beauty products (e.g., mascara), and avoiding known allergic agents or persons with conjunctivitis.

Glaucoma Glaucoma is an insidious, painless dis- ease that typically results from pressure building up in the anterior chamber of the eye or the space in front of the lens. This condition is known as chronic glaucoma and will be discussed here; however, there is acute glaucoma, which is ac- companied by intense pain and blurriness. In acute cases intraocular pressure must be relieved immediately to reduce pain and to save vision.

The aqueous humor made by the ciliary body apparatus is produced at a fairly constant rate and normally drains away. But in glaucoma, fluid accumulates and increases pressure within the eye. Pressure exceeding twice the normal in- traocular pressure (8–21 mm Hg) causes the retina to start losing its ability to distinguish im- ages clearly. This progression of events contin- ues until a partial to total blindness develops. Peripheral vision is severely reduced if the condi- tion is untreated; then it is lost, and “tunnel vi- sion” ensues as the photoreceptors on the retina are destroyed and continue to deteriorate visual quality (eyesight) (Figure 13–19 �).

A glaucoma gene, GLCA1 on chromosome 1, may account for 10% of the 80,000 to 100,000 new cases per year in the United States. World- wide, glaucoma affects about 66.8 million indi- viduals. Most congenital glaucoma is heredi- tary, while secondary glaucoma is caused by systemic diseases, such as infections, or drugs like corticosteroids. The incidence of glaucoma among black Americans is four times that of white Americans. This disease affects nearly 2% of the population over age 35, or about 3 million

persons in the United States. In Southeast Asia glaucoma is quite common, considering a host of tropical infections and lack of treatment. In- dividuals with a family history or with diabetes should have frequent eye checkups.

The ophthalmoscope is the primary portable tool used by the optical agent to view the inte- rior of the eyeball for general inspection. How- ever, to diagnose glaucoma, a noncontact (“air- puff”) tonometer helps to screen for the disease by bouncing a puff of air off the cornea that flat- tens it slightly and allows a quick register of in- traocular pressure. After first using numbing droplets on the eye, a more accurate measure- ment is done with applanation tonometry, which allows the instrument to touch the cornea lightly. The pressure required to indent the corneal surface is measured, and using a slit lamp (magnifying) device allows the ophthalmol- ogist to explore the whole interior of the eye with bright light and get a three-dimensional view. In this case, the lighted interior tends to show a cupping of the optic disc, where the optic nerve enters the back of the eye.

Drugs like timolol reduce fluid production, and pilocarpine promotes aqueous humor flow. Surgery involves piercing the anterior chamber

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with a laser, which promotes draining and re- duction in pressure and improves vision. Pre- vention is basically genetically determined but includes a healthy diet with adequate intake of vitamin A, and good vision care (e.g., reducing infections via limited hand–eye contact, and wearing eye protection such as sunglasses).

Uveitis The uvea is the second layer of the eye known as the vascular or pigmented layer and includes the ciliary body and the colored part of the eye known as the iris. Inflammation of the uvea may be caused by infectious agents, espe- cially in reduced immune conditions, but uveitis itself has an immunological or neoplastic basis. Symptoms include pain, redness, photophobia, and blurred vision. Depending on if the inflam- matory attack is in front of the lens (anterior) or behind it (posterior), different approaches are taken to insure the best outcome. Anterior in- flammation accounts for about 90% of the cases and usually lends itself to topical corticosteroids. Posterior uveitis requires systemic (internal) medications or intravitreal (in uvea) corticos- teroid therapy, and if bacterial agents are pre- sent, then the appropriate antibiotics would be used. This primarily immune disorder is related to or accompanies many other conditions or dis- eases, from psoriasis to Crohn’s disease. Preva- lence is estimated at 8 per 100,000, with approx- imately 38,000 new cases per year in the United States.

Light and Refractory Distortions Astigmatism Light enters the clear curved cornea. If the cornea is pitted from prior ulcera- tion or is unsymmetrical or has thick and thin sections, it would transmit light to the lens and retina in irregular wavelengths. Similarly, if the lens is warped or irregular, the transmitted light is uneven. Both scenarios give a blurry or un- clear image when the light (image) strikes the retinal surface. This refractory condition is called astigmatism. It may be associated with any other eye condition, like myopia, and may affect one eye or both. The objects viewed might be basi- cally recognizable, but there is always some de- gree of distortion to the overall image. Corrective lenses, including contact lenses, help but may

not fully repair the condition, especially if the ir- regularities are with the internal lens. Cornea ad- justments may be made surgically, or the lens could be replaced. Most individuals tend to ig- nore the minor deficiency and adjust to it.

Myopia and Hyperopia (Nearsightedness and Farsightedness) The more common types of eye problems involve distance. An acuity test done by the famous Snellen chart (E letters) allows determination of a 20/20 (normal) or a range from 20/200 to 20/10 reading for different distance levels. Nearsightedness, or myopia, and farsighted- ness, or hyperopia, as well as astigmatism, de- scribed earlier, are outlined in Figure 13–20 �.

Compared to normal vision, myopia or near- sightedness is noticed when close objects are clear and sharp while more distance objects are blurred. The eyeball is longer than normal, so the image falls short (thus the term short/near sightedness) and does not reach the retina suffi- ciently, leaving a blurry image. It may be that the lens is too thick and thus the image would fall in front of the retina. To correct myopia, a concave lens is required to stretch incoming light rays to reach the retina and give a clear picture. Approximately 70 million adult Ameri- cans have myopia.

In the case of hyperopia, objects at a distance are clear, but those images close up are blurry. About 1 in 4 Americans share this disorder, or almost 61 million people. The eyeball appears too short, or a lens may be too thin. A convex lens is required to bend the light waves more quickly or shorter to strike the retina in a clearly focused fashion. Contact lenses work well, and laser treatments may shave layers off the cornea or lens to improve sight. LASIK surgery, a type of cornea surgery, holds great promise for long- term relief. LASIK surgery eliminates or reduces use of eyeglasses or contact lenses for most nor- mal activities requiring near- or far-sighted vi- sion. For some tasks, reading glasses may still be required. With either case, astigmatism may be an additional part of the visual correction, and that would require a special lens or glasses to offer a sharper image at the retinal surface. The astigmatism may be in one or both eyes and be of varying degree.

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A Hyperopia

B Myopia

C Astigmatism

Vertical

Horizontal

Figure 13–20 � In hyperopia light rays focus behind the retina, making it difficult to focus on objects at close range. In myopia light rays focus in front of the retina, making it difficult to focus on objects that are far away. In astigmatism light rays do not uniformly focus on the eye due to abnormal curvature of cornea or lens.

Presbyopia Presbyopia is an age-related and refractive disorder. About 1 per 11 or 9% of Americans have this condition. At about age 45, the crystalline lens of the eye loses its flexibility and causes a reduction in the ability to focus im- ages on the retina. This may happen rather sud- denly, but the lens has been growing from birth and continues to grow throughout life, so by the time of death the lens has increased in weight by about four times. This change is a normal mod- ification to the eye due to aging, and individuals notice the problem when they hold pictures and written material at arm’s length to get a better view. Optometrists can fit corrective lens like bi- or trifocals or contact lenses for better vision. Be- cause things continue to change, so must the corrective lenses.

Cataracts Cataracts are the result of a clouding of the lens. There are three types of cataracts that correspond to the three layers of the lens. The outer layer is a clear membrane or capsule, the middle zone is composed of soft clear material called the cortex, and the core is the least flexi- ble site called the nucleus. The cause of cataracts is not known, but they have been attributed to a congenital defect, eye trauma, the effects of tox- ins, and aging. The main symptom is fading and distortion of vision. Additional lighting is useful early on, especially for printed material, and this helps clue the person as to an impending visual impairment.

By age 65, almost half of all Americans have some degree of cataracts and thus impaired vi- sion, and after age 75 the figure is close to 70%. Usually by the eighth decade, cataracts have be- come more evident or ripe. A routine (general) eye exam, using ophthalmoscopy, normally de- tects early stages of cataracts. This detection al- lows planning for treatment if needed or preven- tative measures to reduce the progression of cataract development, such as avoiding bright light and wearing sunglasses. A new measuring device called an aberrometer allows a better record of the status of the eye and assists the preparation of LASIK surgery to match or exceed what glasses or contact lenses do for sight. The patient looks at a pattern of faint red lights, and the machine makes detailed optical measure-

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Figure 13–22 � Age-related macular degeneration demon- strating loss of central vision. (National Eye Institute)

ments as it inspects the interior of the eyeball. This procedure is simple, painless, and is done in the doctor’s office. In the past, treatment was usually nonspecific or withheld, and with time the lens was surgically replaced. Outpatient surgery for lens replacement including lenses for 20/20 vision or bifocals, has become a rou- tine procedure, and vision is restored to normal in patients 95% of the time. Prevention is almost impossible for an age-related condition or in the face of a concurrent disease (e.g., diabetes or syphilis). However, avoiding harmful drugs or chemicals and direct sunlight can postpone this common disorder. (See Figure 13–21 �.)

Retinal Image Defects Macular Degeneration Macular degeneration is the reduction or loss of acute vision. Macular degeneration develops in 10% of the elderly and affects both eyes, affecting only central vision and leaving peripheral vision intact. There are two forms of macular degeneration: the atrophic (dry) version, comprising 70+% of the cases, and the exudative (wet, hemorrhagic) type, a more de- structive version. (See Figure 13–22 �.)

Causes for this degeneration are not well un- derstood, but it is known that obstructed blood flow, followed by revascularization (as occurs in atherosclerosis), compromises the area of the

retina responsible for acute vision. Other con- tributing factors are injury, inflammation, infec- tion, and heredity.

Diagnosis is by direct eye exam with ophthal- mascope and fluorescein angiography, which reveal leaking vessels in the subretinal area. There is no cure for the atrophic case, but 5% to 10% reduction in the exudative condition can be accomplished by using an argon laser to cause photocoagulation.

Diabetic Retinopathy About 40% of the dia- betes type 1 patients will be diagnosed with dia- betic retinopathy (DR) within 3 years of diabetes diagnosis. Depending on the intensity of the di- abetes and patient’s age, it may be a mild abnor- mality or a major factor causing loss of eye sight. It is the leading cause of new blindness in adults aged 20 to 65; as diabetes diagnoses continue to rise in the United States, related diseases will in- crease as well. In type 2 diabetes, about 20% of the cases have DR at the time of diagnosis. Screening involves dilated pupils and ophthal- moscopy, which may become routine annual

Figure 13–21 � Cataracts show the whole image as blurry. (National Eye Institute)

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events with eye checkups. Special attention must be given to those pregnant or attempting to be- come pregnant. This monitoring is done primar- ily through diabetes control measures, like blood glucose levels, and kidney functioning plus blood pressure measurements. In exudative cases, leakage can be abated by using an argon laser to cause photocoagulation. Prevention is unlikely considering the universal effect over the body that diabetes mellitus presents.

Retinitis Pigmentosa Retinititis pigmentosa is a genetic disease either as a recessive or dominant trait on the X chromosome. Other forms may exist, but it is a rare, progressive retina degeneration that eventually causes blindness. The symptoms of weakened sight start in childhood and slowly en- croach peripherally and cause tunnel vision, some- what like glaucoma. A special electroretinogram that measures the retina and its response to light determines the disease and its status. No partic- ular treatment is known, although some success has been noted with fetal retinal tissue transplant. Retinal detachment is possible here as well, and that causes more complications for treatment.

The optic nerve may be a part of the visual disturbance pattern, and that may be caused by physical strain, such as trauma or pressure (stretching) in the event of exophthalmos, as found in hyperthyroidism. With various toxins (especially heavy metals), low oxygen levels, and drugs (including Viagra), the optic nerve is sen- sitive to many factors injurious to eye sight. Blindness normally develops when light is blocked to the retina as in cataracts and when there is increased intraocular pressure as in glaucoma, optic nerve damage, or image failure recognition by the occipital cortex. Regardless of cause, the best way to prevent visual impair- ment is to practice good hygiene (e.g., avoid un- necessary hand-eye contact), observe safety precautions, and seek medical help with any noticeable eye problem.

The Ear Hearing loss is a major problem for those with normal acoustic function, and there are three categories of hearing loss: conductive, mainly a blockage or physical problem; sensory loss due

to inner ear elements being lost or compro- mised; and neural hearing loss from damage to the auditory nerve (VIII). Age can be a major fac- tor in hearing disabilities along with the enviri- onmental workplace and modern instrumenta- tion, like cell phones and personal audio devices, that put a significant stress on hearing abilities. More than 28 million Americans are deaf or have hearing loss, and each year sudden deafness occurs among 1 per 5000, particularly the elderly.

Conductive hearing loss is commonly caused by excess ear wax buildup (cerumen im- paction), a tumor, or pus buildup in the audi- tory canal or middle ear from infection (external otitis, otitis media). The middle ear bony ossi- cles may stiffen as in arthritis, called otoscler- osis, and a perforated ear drum is a frequent occurrence. All of these situations reduce hear- ing abilities and require different modes or pro- cedures to correct them. External and middle ear infection are common events, especially in children, and these dysfunctional disorders are now addressed.

External Ear The visible part of the external ear is known as the auricle or pinna and it enhances hearing perception by a small percent (2% to 4%). It assists hearing by collecting sound waves and funneling them down the auditory canal and is subject to skin cancer, primarily from sun expo- sure, and trauma from accidents or athletic ac- tivities. Skin cancer is treated mainly by surgery. Trauma cases may require surgery as well and to prevent disfigurement (such as a “cauliflower” appearance). Cosmetically, auricle design or size may be an issue, especially for children when the auricles are extra large or protrude and appear unsymmetrical. Infections can occur when pierced earring sites are not properly cleaned, and some metals cause allergic reactions. Pro- tecting the ear from severe environmental ex- tremes and using ear plugs for noise reduction are effective preventive measures for reducing hearing loss. (See Figure 13–23 �.)

Cerumen Impaction Wax is necessary for the soft texture and flexibility of the ear drum. How- ever, cerumen impaction or excess wax buildup may recur, especially in youngsters or the elderly.

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Outer ear Middle

ear Inner ear (labyrinth)

Auricle

Helix

Lobe

Semicircular canals

Vestibular nerve

Cochlea

Cochlear nerve

External auditory canal

Tympanic membrane (eardrum)

Ossicles Malleus Incus

Auditory (eustachian) tube

Stapes

Round window

Oval window

Vestibule

Figure 13–23 � Human ear anatomy.

Upon first appearance of wax building, better hy- giene is required. The buildup is usually allevi- ated by heated water, oil treatment, hydrogen peroxide (3%), or alcohol drops as simple reme- dies. However, on occasion a suction action or mechanical removal is necessary. It is impera- tive to have an intact ear drum when performing any treatment, and be sure to dry the ear area completely following treatment. Prevention is

possible through routinely checking the ear canal for signs of wax accumulation.

External Otitis External otitis, or “swimmer’s ear,” is an infection caused by bacteria and fungi. Symptoms and signs include pain, pruritis, fever, and (temporarily) hearing loss.

The pathogens responsible for external otitis are found in contaminated swimming pools or

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beaches. Drying the external ear opening after bathing or swimming and cleaning earphones, earplugs, and earmuffs can prevent it. Treat- ment with antibiotics is effective for bacterial in- fections, but some fungus infections may be more stubborn to control.

Otitis Media Acute otitis media is a middle ear infection that affects primarily infants and chil- dren because of weak immune systems and per- haps the lack of breast feeding. Symptoms in- clude pain and edema, with pus, and left unchecked the condition may cause perforation of the tympanic membrane (ear drum). Otitis media often follows pneumonia or an upper res- piratory infection (URI), such as sinusitis. Most often, bacteria are the cause. Children are more susceptible than adults to middle ear infections because their nearly horizontal auditory tubes prevent adequate drainage. Diagnosis is primar- ily done by observation of pus in the ear canal and complaint of earache. Pain can be controlled with analgesics, and swelling is reduced by use of decongestants. To relieve pressure and allow pus to drain, small ear tubes like tiny cylinders are placed through the ear drum (tympanic mem- brane) to allow air into the middle ear. They are called tympanostomy tubes or myringotomy tubes, or simply ventilation tubes. In recurrent cases, scarring of the ear drum, auditory ossi- cles, and inner ear components can occur. There is potential for invasion of the nearby mastoid area, a honeycombed sinus area, and this pene- tration results in mastoiditis. With mastoiditis comes a fever and the possibility of brain infec- tion or abscess formation because of the rela- tively thin membrane between the sinus area and the brain vault. In undeveloped countries with inadequate access to health care and antibiotics, chronic otitis media and its complications are very common among both adults and children. Penicillin-type antibiotics help, but in some resis- tant cases like Pseudomonas aeruginosa, stronger agents are required.

For chronic otitis media there may be relief. A clinical test study funded by NIH and published in 2005, using a device called the EarPopper, had an efficacy (effectiveness) rate of about 85% for those tested. This tool sends a gentle stream

of air into the nasal cavity, and as the individual swallows, it forces open the Eustachian tube (or auditory tube) and equalizes the pressure within the middle ear. If fluid is present, it may take two treatments per day for a few weeks, but the benefit is that ear surgery is not required. This device is safe, basically pain free, and can used by anyone, including children.

Inner Ear The inner ear consists of the semicir- cular canals (which, along with the cerebellum, maintain equilibrium) and the snail-like device called the cochlea. The semicircular canals work like a carpenter’s level, with a bubble floating in a sea of fluid, to give the sense of balance and being upright. In addition, at the base where the three semicircular canals meet and form a con- nection with the cochlea, stiff ciliated (brushlike) elements attached to neurons line a common chamber. In this same chamber of fluid are grains of “sand,” called otoliths, that tumble or float down like an hourglass and thereby stimu- late the sensory elements to signal the brain as to body positioning or orientation (e.g., turned head). Along with the cerebellum and visual cues, the body maintains a normal standing or sitting posture or comprehends body location.

Some infections may interfere with the func- tioning of semicircular canals. In the case of fever or various drug interactions and elec- trolyte imbalances, the viscosity of the internal fluid may be altered. Vertigo or dizziness may cause nausea or headache and may cause acci- dential stumbling or falling. Acute cases of im- balance that may become episodic or longer- term vertigo would need to be addressed.

The cochlea houses coiled tubes filled with fluid that rushes over miniature “harps” called an organ of Corti and triggers signals to the au- ditory nerve. When these organs of Corti are damaged or lost, the hearing loss is permanent. Loud noises or sounds from heavy equipment, airplanes, and loud music; or ototoxic drugs like some chemotherapy drugs; and various infective agents leave a scar on the hearing apparatus.

As with sight and age, hearing too has its lim- itations, called presbycusis. This conditition is the most common cause of sensorineural hear- ing loss in adults. The actual cause is not

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known, but the condition tends to run in fami- lies and progresses with age. Constant exposure to loud noises gives ample reason to wear de- vices (earplugs) to protect the natural hearing mechanism. About 25% of those age 65 to 75 have measurable hearing loss, in part due to age, and about half those over age 75 have pres- bycusis. Hearing aids help restore some sound, but clarity is somewhat sacrificed.

Neural loss involving the eighth cranial nerve (vestibulocochlear) or auditory nerve has many possibilities. If the nerve is damaged by trauma, high fever, toxins, or other agents, the loss may be permanent. Experiments have used nerves located in the back and other areas, but without the auditory nerve connection to the temporal lobe of the brain, it is basically impossible to have the sounds clearly interpreted.

Deafness has its genetic component, as when a baby is born deaf, and cochlear implants are often used to overcome deafness. Inheritance of deafness may be either dominant or recessive, and over 100 genes have been identified as in- strumental in this deficiency. The connexin-26 mutation has been suggested as a prevalent form of recessive hearing loss. Mitochondrial (cell organelle) disorders and hearing loss also play a significant role in the complex mecha- nism of auditory challenge. Whatever the cir- cumstance, it is critical to save and protect all areas of the auditory pathway for the melodies of sound; cochlear implants are a viable alterna- tive when hearing is lost.

Ménière’s Disease The occurrence of Ménière’s disease is at 0.5 to 7.5 per 1000 and usually oc- curs in the mid- to late forties. Primarily consid- ered idiopathic, some cases may be initiated by trauma, tumor, or autoimmune diseases that im- pact the cochlear apparatus whereby fluid and delicate sensory hairs are altered or degenerated. Ménière’s disease is characterized by intermit- tent hearing loss, tinnitus (see below), and episodes of vertigo or dizziness. Therapy is fo- cused on vertigo. Diuretics and restricted salt in- take control fluid levels, and short-term gluco- corticoids reduce inflammatory activity. Surgery may be a later option, but some loss of hearing may occur. Many individuals live with this dis- ease if dizzy spells are reasonably under control.

Tinnitus Tinnitus is defined as the perception of ringing, buzzing, or roaring sounds from an environment void of sound. The cause or patho- physiology of tinnitus is not well known, perhaps because there are many causes and tinnitus may be just one indication among many of other dis- ease attributes. At least 12 million Americans have tinnitus, and 1 million have it severely enough that it interferes with daily life. This de- velopment may involve either conductive or sen- sorineural hearing loss. A full examination is re- quired of the ear, nose, and throat to discern problems like infection, trauma, or growths, plus family history and and any drug regimen. Diag- nosis is similar to other ear investigation and be- gins with the Weber and Rinne tuning fork test. Not only are the frequencies or pitch of the sound noted, but more so, whether the limitation is con- ductive or sensorineural. The stem of the vibrat- ing fork is placed on the skull near the mastoid process (just behind and under the ear), or maybe the teeth, to tell if a sound is louder or softer compared to the sound in air. If the sound is louder in air versus the contacted bone, then it appears to be a sensorineural insufficiency, and if louder by bone contact, it appears to be a conduction defect.

Tinnitus is known to be affected by, or is part of, a hearing loss problem because of excesive loud noise exposure, poor reaction to some medications, or various other health concerns. Treatment by the otolaryngologist includes hear- ing aids to overpower the background sounds, sound-masking devices to cancel or reduce the ringing noises, amplifier devices on phones, or eletronic equipment to pick up better-quality sound, plus medications and relaxing tech- niques. People with tinnitus should avoid loud sounds and be patient; some may find that lipoflavanoid supplementation is helpful. Lipo- flavanoid is a dietary supplement used since the 1960s to specifially improve the microcircu- lation within the inner ear. Therefore, the flexi- bility of the sensory hair cells responsible for sound transmission to the brain is maintained and the fluid within the cochlear canals flows easier. Lipoflavanoid improves inner ear health and reduces the intensity of ear ringing found in tinnitus as well as symptoms found in Ménière’s syndrome.

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All senses make for a more enjoyable life. Any reduced stress promotes better homeostasis, and that means a healthier and better exis- tence. The olfactory sensation, mentioned in Chapter 8, may add pleasure or displeasure to the environment and thus necessary for detect- ing methane gas or rotten odors from spoiled food sources; thus a the sense of smell could help prevent illness or save a life, both of which could be fatal. Similarly, the sense of taste (gus- tatory) is necessary to detect rotten, toxic, or pleasurable attributes of our living arena. Taste and smell often diminish with age, disease, and drugs like chemotherapy treatments. Zinc sup- plements seem to offer some relief in the case of reduced gustatory abilities and allow for a more pleasant taste of life.

Age-Related Diseases

Neurological disease affects individuals at all stages of life. Glaucoma and cataracts are age- related visual problems, as is presbyopia, a lens condition that occurs usually in the mid-40s. In presbyopia, the lens becomes less resilient and remains relatively flat, leaving distance vision

▼

intact but impairing near vision. Corrective lenses are very common after age 43 to 45. Mac- ular degeneration typically comes along with age, as do cataracts and difficulty hearing (called presbycusis). Tinnitus, an ear ringing sensation, normally develops in later years due to environmental or unknown factors. Cranial nerve dysfunction usually occurs in young and middle-aged adults. Alzheimer’s disease (see Chapter 14) is a prominent concern for seniors. The incidence of dementia and of Parkinson’s disease increases with age. In trisomy 21 (Down syndrome), patients who live past age 45 tend to have AD.

Finally, with age, the 3-pound brain reduces in weight and size, with concurrent loss of neu- rons and synapses. Thus, it is understandable that functional losses in hearing, sight, and co- ordination will be experienced in the elderly. Reaction times are reduced, and so is agility, which increases risks for injury.

R E S O U R C E

National Institutes of Allergy and Infectious Diseases: www.nei.nih.gov

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DISEASES AT A GLANCE Nervous System and Special Senses

DISEASE ETIOLOGY SIGNS AND SYMPTOMS

Glioma, glioblastoma Idiopathic Severe headache, personality changes, loss of speech, unsteady movement, seizures, coma

Meningitis Bacterial, viral High fever, chills, severe headache, stiff neck, nausea, vomiting, rash, delirium, convulsions, coma

Encephalitis Viral Mild to severe headache, fever, cerebral dysfunction, disordered thought, seizures, persistent drowsiness, delirium, coma

Poliomyelitis Viral Stiff neck, fever, headache, sore throat, GI disturbances, paralysis may develop

Tetanus Clostridium tetani Rigidity of muscles, painful spasms and convulsions, stiff neck, difficulty swallowing, clenched jaws

Rabies Viral Fever, pain, mental derangement, rage, convulsions, paralysis, profuse sticky saliva, throat muscle spasm produces hydrophobia

Shingles Varicella, herpes zoster Painful rash of small water blisters with red rim, lesions follow a sensory nerve, confined to one side of body, severe itching, scarring

Reye’s syndrome Idiopathic or viral; Epstein-Barr, influenza B, varicella

Persistent vomiting, rash, lethargy about 1 week after a viral infection, may progress to coma; linked with use of aspirin

Abscess Pyogenic bacteria Fever, headache

Multiple sclerosis (MS) Idiopathic, suspect viral or autoimmune

Muscle impairment, double vision, nystagmus, loss of balance, poor coordination, tingling and numbing sensation, shaking tremor, muscular weakness, emotional changes, remission and exacerbation

Amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease

Idiopathic Disturbed motility; fasciculations; atrophy of muscles in hands, forearms, and legs; impaired speech and swallowing; death from pulmonary failure in 3 to 4 years ISB

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DIAGNOSIS TREATMENT PREVENTION LIFESPAN

CT scan, MRI Surgery, chemotherapy, radiation Uncertain Any age, usually adult

Lumbar puncture (spinal tap) Antibiotics if bacterial infection Be aware, avoid contact Can occur at any age

Lumbar puncture (spinal tap) Control fever, control fluid and electrolyte balance, monitor respiratory and kidney function

Depends on circumstance Can occur at any age

Physical exam Supportive; preventive vaccination

Vaccine Usually younger to early adult

Physical exam, patient history Antitoxin, symptom relief, preventive vaccination

Vaccine Can occur at any age

Physical exam, history of animal bite

Vaccination before disease develops; fatal once CNS involved

Vaccine, be alert Can occur at any age

Physical exam Alleviation of symptoms and pain relief, steroids

Avoid contact,vaccine Usually 50+

Patient history, liver enlargement, hypoglycemia, ammonia in blood

Supportive; close monitoring necessary

Avoid aspirin, Seek care Infants, young children

Lumbar puncture (spinal tap) Surgical draining of abscess, antibiotics

Quick treatment Can occur at any age

Physical exam, patient history, MRI

None effective; physical therapy and muscle relaxants, steroids, counseling

Basically autoimmune and polygenetic

Midlife

Electromyelography (EMG) Supportive Uncertain Midlife

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380 ■ Chapter Thirteen Diseases of the Nervous System and the Special Senses

DISEASES AT A GLANCE Nervous System and Special Senses (continued)

DISEASE ETIOLOGY SIGNS AND SYMPTOMS

Huntington’s disease (Huntington’s chorea)

Genetic Involuntary, rapid, jerky movements; speech loss; difficulty swallowing; personality changes; carelessness; poor judgment; impaired memory; mental incompetence

Convulsion: epilepsy Trauma, chemical, idiopathic Involuntary contractions or series of contractions; a seizure is a sign of illness, not a disease. Petit mal: brief loss of consciousness, “absence seizure” Grand mal: often preceded by aura (various sensations), total loss of consciousness, generalized convulsions, hypersalivation; incontinence may occur

Spina bifida Congential, lack folate Opening in vertebral canal; spina bifida occulta: hidden; meningocele: meninges protrude; meningomyelocele: nerve elements protrude; myelocele: nerve tissue disorganized

Hydrocephalus Congenital, idiopathic Enlarged head develops

Cerebral palsy Birth trauma, rubella infection Seizures, visual or auditory impairment, speech defects. Spastic: muscles tense, reflexes exaggerated. Athetoid: uncontrollable, persistent movements, tremor. Atactic: poor balance, poor muscular coordination, staggering gait

Transient ischemic attacks (TIA), “mini strokes”

Ischemia, aneurysm, hypertension

Visual disturbances, transient muscle weakness on one side, sensory loss on one side, slurred speech; attacks last minutes to hours, average 15 minutes

Cerebrovascular accident (CVA) stroke, brain attack

Trauma Severe, sudden headache; muscular weakness or paralysis; disturbance of speech; loss of consciousness

Alzheimers’s disease Idiopathic, but genetically connected

Memory loss, moody, indigent

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DIAGNOSIS TREATMENT PREVENTION LIFESPAN

Patient history (inherited disease) and physical exam

No cure; genetic counseling for family

Totally genetic Age 35+

Observation of seizure, electroencephalogram (EEG), x-ray, family history, CT scan, MRI

Removal of cause once detected; anticonvulsive drugs

Avoid cranial trauma; use helmet or headgear

Can occur at any age

Physical exam, CT scan, MRI, EEG

Surgical, physical therapy Variable, folate supplements

Middle-aged mother

Physical exam, CT scan, MRI, spinal tap

Implant shunt to drain CSF Variable to pathogen exposure

Can occur at any age, but more prevalent among newborns

Physical exam Muscle relaxants, anticonvulsive drugs, casts, braces, traction, surgery, physical therapy

Variable, birth caution Can occur at any age

Cerebral angiogram, CT scan Depends on cause; surgical treatment of blocked vessels

Blood pressure monitoring, uncertain

Usually middle age

Angiography, CT scan, MRI Clot-dissolving drugs, surgery, endarterectomy

Uncertain, family history, keep low blood pressure levels

Usually mid life+

Behavioral, clinical screening Care facilities, medications to stay calm

None with long survival Onset-mid age, progressive with time

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382 ■ Chapter Thirteen Diseases of the Nervous System and the Special Senses

DISEASES AT A GLANCE Nervous System and Special Senses (continued)

DISEASE ETIOLOGY SIGNS AND SYMPTOMS

Special Senses: Eye

Conjunctivitis Viral, bacterial Inflamed eye surface, oozing

Glaucoma Poor aqueous fluid drainage Elevate intraocular pressure, dim vison

Uveitis Infectious agents Eye discharge, pain, low vision

Astigmatism Irregular cornea or lens Blurry vision

Cataracts Cloudy lens Blurred, dim vision

Macular degeneration Idiopathic Central vision lost

Diabetic retinopathy Diabetes Blurred, cloudy vision to blinded

Retinitis pigmentosa X chromosome Weakened sight gradual blindness

Special Senses: Ear

External otitis Infection Discharge, pus

Otitis media Infection Internal fluid pressure,fever

Presbycusis Increased age Hard of hearing

Ménière’s disease Idiopathic, trauma, autoimmune? Vertigo, disoriented, tinnitus

Tinnitus Idiopathic, may be blood pressure related, loud sounds

Ringing, roaring internal sounds without real sounds externally

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DIAGNOSIS TREATMENT PREVENTION LIFESPAN

Eye inspection, environment, eye fluids

None or ointment or eye drops Contagious, avoid contact Usually young child, but not determined by age

Ophthalmoscope and slit-scope Eye drops None, 10% genetic Mid age+

Eye exam Corticoids Basically autoimmune Variable

Chart exam, eye inspection Corrective lenses None NDA

Ophthalmoscope Some laser, lens replacement None, avoid sunlight, STDs Usually elderly

Ophthalmoscope Nonspecific None Older persons

Ophthalmoscope and fluorescein angiography

Some laser, control diabetes and blood pressure

Perhaps control diabetes More likely with aging

Electroretinogram Nonspecific None From birth

Ear inspection Antibiotic, cleanse area Depends, use good hygiene, keep ear canal dry

Can occur at any age

Ear inspection Drain tube, antibiotics Depends, use good hygiene Children +

Audio testing Hearing aids None Worse with age

Hearing test and exam Glucocoricoid, low salt diet Uncertain Age 40+

Hearing test Sound aids, low sound makers for interference

Depends Usually middle aged, but expected in younger people following loud music performances

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6. Which of the following applies to MS?

a. occurs only in males b. occurs primarily in east European cultures c. results from a damaged myelin sheath d. strikes adults age 20 or beyond

7. Within 3 to 4 hours, what clot-buster may be used to treat the most common form of CVA?

a. aspirin b. TPA c. ATP d. hemolase

8. What disease has a seizure symptom known as petit mal?

a. polio b. MS c. epilepsy d. encephalitis

9. What is the lesion in Parkinson’s disease?

a. no dopamine b. no myelin c. autoimmunity d. cerebral blood clot

10. Pauly, a first-grader, woke one morning to discover a blood- shot right eye and a yellowish mass near the medial corner of his eye. What is the correct diagnosis?

a. common cold b. trachoma c. conjunctivitis d. osteitis

1. What is the infective agent for rabies?

a. bacterium b. virus c. fungus d. tick

2. Which of the following may cause epilepsy?

a. a birth trauma b. injury to the brain c. a penetrating wound d. all of these

3. What functions are controlled by the brain stem?

a. sensory function b. muscle action c. memory d. heart rate and breathing

4. What is called an acute inflammation of the first two meninges of the brain and spinal cord, the pia mater and the arachnoid?

a. thrombophlebitis b. meningitis c. prostatitis d. encephalitis

5. Which of the following is true of polio?

a. is caused by a virus b. affects sensory neurons c. is found in most people by age 80 d. was wiped out in 1976

The vision in the right eye was foggy, dim, and not focused. There was essentially no pain. What do the symptoms sug- gest? What are the prognosis and treatments for this woman?

3. T. C. complained of an earache, and after a recent bout with a bad cold, he was rather irritable. The ear was “beet red” and felt warm. He could hardly hear on that side, but he knew there was nothing intentionally or accidentally poked into the ear. What disease best explains these symptoms? Give some recommendations for treatment.

1. J. A. has had a severe headache for the last 12 hours, a fever of 102, plus a stiff neck. Following a lumbar puncture, Streptococcus pneumoniae was found in culture along with low sugar levels and higher protein values. What disease best explains these findings? What is the prognosis and treatment?

2. At age 78, K. B. started rubbing her eyes and constantly cleaning her (old) glasses for a better view. The right eye particularly was not very good, and she hoped the problem, which she first noticed months ago, would finally go away.

384 ■ Chapter Thirteen Diseases of the Nervous System and the Special Senses

Interactive Exercises

Cases for Critical Thinking

Multiple Choice

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True or False

_______ 1. Rabies is a viral infection.

_______ 2. The Sabin vaccine works in the digestive tract.

_______ 3. Oxygen under high pressure is effective in treating rabies.

_______ 4. Blood is not normally found in cerebrospinal fluid.

_______ 5. Dopamine deficiency causes epilepsy.

_______ 6. Transient ischemic attacks are characterized by loss of consciousness.

_______ 7. An aura is a flashback of previous contusion events.

_______ 8. Viral meningitis requires quarantine isolation procedures.

_______ 9. Excess Dilantin may cause Parkinson’s disease.

_______ 10. Conjunctivitis is usually a viral attack in adults.

Fill-Ins

1. ____________________, commonly called lockjaw, is an infection of nerve tissue caused by the tetanus bacillus that lives in the intestines of animals and human beings.

2. Amyotrophic lateral sclerosis is diagnosed by ____________________.

3. ____________________ ____________________ is a chronic, progressive disease of the central nervous system with myelin destruction.

4. ____________________ ____________________, also known as shaking palsy, is a disease of brain degeneration that appears gradually and progresses slowly.

5. The common drug given to victims of Parkinson’s disease is ____________________.

6. ____________________ headaches are severe, are unilateral, involve the periorbital and orbital area, and typically occur in men.

7. Tic douloureau, or ____________________ ____________________, causes severe pain elicited from cranial nerve V.

8. ____________________ ____________________ is a unilateral dysfunction of muscles in the face that leaves the person with slurred speech and a watery eye.

9. ____________________ is called Lou Gerhig’s disease.

10. ____________________ is the worst form of spina bifida.

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386 ■ Chapter Thirteen Diseases of the Nervous System and the Special Senses

Labeling Exercise

Use the blank lines below to label the following image.

1 2

5 10

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Multimedia Preview

Additional interactive resources and activities for this chapter can be found on the Companion Web- site. For videos, audio glossary, and review, access the accompanying DVD-ROM in this book.

DVD-ROM Highlights▼

Beat the Clock Do you know your diseases? Test your smarts against the clock in this game of knowledge, spelling, and speed. Can you correctly answer 20 questions before the final tick?

Vocabulary 911 Someone call 911, it’s a human disease emergency! Test your knowledge by helping the injured word into the correct ambulance.

Case Study Take advantage of the free-access online study guide that accompanies your textbook. Put your under- standing of human diseases to the test with this real- world scenario. You’ll be presented with a clinical case followed by a series of questions that challenge your grasp of the situation. By clicking on this URL you’ll also access links to current news articles and an audio glossary.

Website Highlights—www.pearsonhighered.com/zelman▼

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