Psych210 quiz2&exam

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Movement

Chapter 8

• Muscles make up the majority of the human body’s tissues – Responsible for the movement of the body

and the movement of materials within the body.

• The human body contains somewhere between 640 and 850 skeletal muscles

Muscles

• Smooth muscle – Found in the lining of the digestive tract,

within arteries, and in the reproductive system – Controlled by the autonomic nervous system.

• Striated muscle: named for its striped appearance – Cardiac muscle: found in the heart – Skeletal muscles: attached to bones

• Responsible for the majority of body movements

Types of Muscle

The Muscle Types in the Human Body

• The muscle fiber is a long, thin cell that usually runs the length of the muscle itself

• The muscle fiber membrane – Contains receptor sites for acetylcholine – Action potential produces single contraction or

twitch

Muscle Anatomy and Contraction

• Long strands of protein that run length of muscle fiber

• Sarcomere: single segment of a myofibril • Z line: boundary of each sarcomere • Filaments of proteins actin and myosin lie

on each Z line

The Structure of Myofibrils

• Movement of thick myosin filaments along length of actin filaments

• Caused by the movement of the thick myosin filaments along the length of the thin actin filaments

Muscle Fiber Contraction

The Anatomy of a Muscle

Muscle Contraction

• Slow-twitch (Type I); fast-twitch (Type IIa and IIb)

Fiber Types and Speed

• Exercise builds muscle in response to muscle fiber damage – As a result, more actin and myosin filaments

are produced – Lack of activity reverses this process quickly

• In space travel, astronauts can lose as much as 20 percent of their muscle mass in as little as two weeks

Effects of Exercise on Muscle

• Loss of muscle mass begins at about age 25 and accelerates throughout one’s life span

• Muscle mass diminishes to about 50% by age 80

Effects of Aging on Muscles

Effects of Aging on Muscle Fibers

• Alpha motor neurons – Spinal motor neurons responsible for

contracting muscles – Capable of rapid firing

• Neuromuscular junction – Where alpha motor neurons meet muscle

fibers

Neural Control of Muscles

• Made up of a single alpha motor neuron and all the muscle fibers it innervates

• Can include fast- or slow-twitch fibers but not a mixture of both

• Motor units for fast-twitch fibers generate 100 times the force of slow-twitch fibers

The Motor Unit

• Two methods for controlling the force of our movements – Rate code: Vary firing rate of motor neurons – Recruitment: an increased demand “recruits”

more motor units

The Control of Muscle Contractions

Spinal Motor Neurons

Neuromuscular Junctions

• Alpha motor neurons require input from three types of neurons to initiate movement – Muscle spindle: specialized sensors that help to

form the feedback loop from muscle fiber to spinal cord

– Golgi tendon organs: provide feedback about degree of muscle contraction, or force

– Joints: provide information about position and movement from mechanoreceptors in tissue around each joint

The Control of Spinal Motor Neurons

Types of Muscle Spindle Fibers

• Myotatic reflex – Responds to sensing stretch – Examples of monosynaptic reflexes, in which

only a single synapse between a sensory neuron and a motor neuron is involved

Feedback from the Muscle Spindle

An Example of a Myotatic Reflex

Muscle Spindle Provide Feedback about Muscle Length

Golgi Tendon Organs Provide Feedback about Muscle Contraction

• Monosynapatic reflexes – Reflex that requires the interaction of only two

neurons at a single synapse • Polysynaptic reflexes

– Involve more than one synapse

Reflex Control of Movement

• Reflexes of the life span – Some reflexes are present in early childhood

and then diminish as the nervous system matures

– Reappearance of immature reflex in adult can indicate brain damage or use of alcohol or drugs

Reflex Control of Movement (cont’d.)

Reciprocal Inhibition at Joints

• Protection from further injury when sensory neurons perceive pain – Example: touching a hot stove – Modulated by the spinal cord

The Flexor Reflex

Spinal Reflexes Related to Walking

• A polysynaptic reflex present in infants and in adults with neural damage, in which stroking the sole of the foot causes the toes to spread with the big toe pointing upward

Babinski Sign

• Lateral pathways – Originates in the cerebral cortex – Voluntary movements

• Ventromedial pathways – Originates in the brainstem – Subconscious, automatic movements of the

neck and torso

Motor Systems of the Brain – Spinal Motor Pathways

Lateral and Ventromedial Pathways

• The cerebellum – Important role in sequencing of complex

movements • The basal ganglia

– Collection of large nuclei embedded within white matter of cerebral hemispheres

– Participate in choice and initiation of voluntary movements

Motor Systems of the Brain

The Basal Ganglia Participate in Voluntary Movements

• Located in precentral gyrus • Main source of voluntary motor control

– The initiation and awareness of movement is a result of increased activity in frontal and parietal lobes

– Movement is encoded by populations of motor neurons rather than by single cells

– Mirror neurons fire when an individual carries out an action or watches another individual carrying out the same act

The Motor Cortex

The Motor Homunculus

The Initiation of Voluntary Movement

The Direction of Movement is Encoded by Populations of Neurons

• Toxins – Many are cholinergic agonists that interact

with acetylcholine at synapses within motor system

– Cholinergic antagonists are generally far more dangerous and potent

Disorders of Movement

Sarin – A Deadly Neurotoxin

• Person’s immune system produces antibodies that bind to the nicotinic ACh receptor – Extreme muscle weakness and fatigue

• Treated with immunosuppressants

Myasthenia Gravis

• Group of inherited diseases characterized by muscle degeneration – A sex-linked disorder typically affecting males – No effective treatments

Muscular Dystrophy

• Contagious virus that targets and destroys spinal alpha motor neurons

• Symptoms can include: – Muscle weakness and paralysis, usually of

the legs – Impaired breathing in more severe cases

• Iron lung

• Worldwide eradication, due to vaccines, is almost imminent

Polio

• Usually results in permanent paralysis of the muscles served by neurons below the level of damage

• Some promising treatment options, but permanent injury

Accidental Spinal Cord Damage

• Degeneration of the motor neurons in the spinal cord and brain stem

• Cause is unknown – 90% of cases have no family history – Correlation with lean body mass and athletic

activity • No effective treatments

Amyotrophic Lateral Sclerosis (Lou Gehrig’s Disease)

• Progressive difficulty in all movements, muscle tremors, and frozen facial expressions

• Dopaminergic neurons of the substantia nigra begin to degenerate

Parkinson’s Disease

• Causes are unknown – Genetics play a role in early-onset but not in

late-onset – Exposure to environmental toxins – Head injury – Correlation with lack of coffee use

• Drug treatment of choice: l-dopa • Surgical treatments: pallidotomy,

thalamotomy

Parkinson’s Disease (cont’d.)

Deep Brain Stimulation Treatment for Parkinson’s Disease

• Progressive disease that produces involuntary, jerky movements and cognitive symptoms

• Caused by abnormality on gene on chromosome 4

• No cure or effective treatments • Death occurs 15 or 20 years after onset of

symptoms

Huntington’s Disease

Degeneration Caused by Huntington’s Disease