Research Report

Anyel1997

fap11-ch17-ada-lecture-presentation.pptx

Home >Biology homework help >Anatomy homework help >Research Report

Lecture PowerPoint

Accessibility standards-compliant

Fundamentals of Anatomy & Physiology

Eleventh Edition

Chapter 17

The Special Senses

Lecture Presentation by

Deborah A. Hutchinson

Seattle University

Learning Outcomes (1 of 2)

17-1 Describe the sensory organs of smell, trace the olfactory pathways to their destinations in the brain, and explain the physiological basis of olfactory discrimination.

17-2 Describe the sensory organs of taste, trace the gustatory pathways to their destinations in the brain, and explain the physiological basis of gustatory discrimination.

17-3 Identify the internal and accessory structures of the eye, and explain the functions of each.

17-4 Describe how refraction and the focusing of light on the retina lead to vision.

Learning Outcomes (2 of 2)

17-5 Explain color and depth perception, describe how light stimulates the production of nerve impulses, and trace the visual pathways to their destinations in the brain.

17-6 Describe the structures of the external, middle, and internal ear, explain their roles n equilibrium and hearing, and trace the pathways for equilibrium and hearing to their destinations in the brain.

An Introduction to the Special Senses

Special senses

Olfaction (smell)

Gustation (taste)

Vision

Equilibrium (balance)

Hearing

17-1 Olfaction, the Sense of Smell (1 of 5)

Learning Outcome: Describe the sensory organs of smell, trace the olfactory pathways to their destinations in the brain, and explain the physiological basis of olfactory discrimination.

Olfaction

Sense of smell

Olfactory organs

Located in nasal cavity on either side of nasal septum

Made up of two layers

Olfactory epithelium

Lamina propria

17-1 Olfaction, the Sense of Smell (2 of 5)

Olfactory epithelium contains

Olfactory sensory neurons

Highly modified nerve cells

Detect dissolved chemicals as they interact with odorant-binding proteins

Supporting cells

Basal epithelial cells (stem cells)

Underlying lamina propria contains

Areolar tissue, blood vessels, and nerves

Olfactory glands (secretions form mucus)

Figure 17-1a The Olfactory Organs.

The olfactory organ on the right side of the nasal septum.

Figure 17-1b The Olfactory Organs.

An olfactory receptor is a modified neuron with multiple cilia-shaped dendrites.

17-1 Olfaction, the Sense of Smell (3 of 5)

Olfactory reception

Begins with binding of odorant to G protein-coupled receptor

Creates generator potential (depolarization)

Olfactory pathways

Afferent fibers leave olfactory epithelium

Collect into 20 or more bundles

Penetrate cribriform plate of ethmoid

Reach olfactory bulbs of cerebrum where first synapse occurs

17-1 Olfaction, the Sense of Smell (4 of 5)

Olfactory pathways

Axons leaving olfactory bulb

Travel along olfactory tract to olfactory cortex, hypothalamus, and limbic system

Olfactory information is the only type of sensory information to reach cerebral cortex directly

All other sensations are relayed from thalamus

Figure 17-2 Olfaction and Gustation (Part 1 of 2).

a) Olfaction

b) Gustation

Figure 17-2 Olfaction and Gustation (Part 2 of 2).

a) Olfaction

b) Gustation

17-1 Olfaction, the Sense of Smell (5 of 5)

Olfactory discrimination

We can distinguish thousands of chemical stimuli

Dogs have 72 times more olfactory receptor surface area than humans do

Thus, their sense of smell is more than 10,000 times better than ours

Olfactory receptors are replaced frequently

But total number of neurons declines with age

17-2 Gustation, the Sense of Taste (1 of 6)

Learning Outcome: Describe the sensory organs of taste, trace the gustatory pathways to their destinations in the brain, and explain the physiological basis of gustatory discrimination.

Gustation (taste)

Provides information about foods and liquids consumed

Gustatory epithelial cells (taste receptors)

Found in taste buds

Distributed on superior surface of tongue and portions of pharynx and larynx

Associated with epithelial projections (lingual papillae) on surface of tongue

17-2 Gustation, the Sense of Taste (2 of 6)

Types of lingual papillae

Filiform papillae

Provide friction to move food around mouth

Do not contain taste buds

Fungiform papillae

Contain about five taste buds each

Vallate papillae

Contain as many as 100 taste buds each

Foliate papillae

Have taste buds

17-2 Gustation, the Sense of Taste (3 of 6)

Taste buds

Contain basal epithelial cells (stem cells)

And gustatory epithelial cells

Extend microvilli (taste hairs) through taste pore

Survive about 10 days before replacement

Innervated by cranial nerves that synapse in solitary nucleus of medulla oblongata

Information travels to thalamus and gustatory cortex of insula

Figure 17-3a Papillae, Taste Buds, and Gustatory Epithelial Cells.

Location of tongue papillae.

Figure 17-3b Papillae, Taste Buds, and Gustatory Epithelial Cells.

The structure and representative locations of the four types of lingual papillae. Taste receptors are located in taste buds, which form packets in the epithelium of fungiform, foliate, and vallate papillae.

Figure 17-3c Papillae, Taste Buds, and Gustatory Epithelial Cells.

Taste buds in a vallate papilla. A diagrammatic view of a taste bud, showing gustatory epithelial cells and supporting cells.

17-2 Gustation, the Sense of Taste (4 of 6)

Gustatory discrimination

Four primary taste sensations

Sweet

Salty

Sour

Bitter

17-2 Gustation, the Sense of Taste (5 of 6)

Two additional taste sensations

Umami

Pleasant, savory taste imparted by glutamate

Characteristic of broths

Water

Detected by water receptors in pharynx

17-2 Gustation, the Sense of Taste (6 of 6)

Taste sensitivity

Differs significantly among individuals

Many conditions are inherited

Example: sensitivity to phenylthiocarbamide (PTC)

Number of taste receptors begins declining rapidly at age 50

Figure 17-2 Olfaction and Gustation (Part 3 of 8).

Gustation

Figure 17-2 Olfaction and Gustation (Part 7 of 8).

17-3 Structures of the Eye (1 of 21)

Learning Outcome: Identify the internal and accessory structures of the eye, and explain the functions of each.

We rely more on vision than on any other special sense

Accessory structures of the eye

Provide protection, lubrication, and support

Include

Eyelids

Superficial epithelium of eye

Lacrimal apparatus

17-3 Structures of the Eye (2 of 21)

Eyelids (palpebrae)

A continuation of skin

Blinking keeps surface of eye lubricated and clean

Palpebral fissure

Gap that separates free margins of upper and lower eyelids

Eyelids are connected at

Medial angle (medial canthus)

Lateral angle (lateral canthus)

17-3 Structures of the Eye (3 of 21)

Eyelids

Eyelashes

Robust hairs

Help prevent foreign matter from reaching eye

Tarsal glands

Secrete lipid-rich product that helps keep eyelids from sticking together

Lacrimal caruncle

Mass of soft tissue at medial angle of eye

Contains glands producing thick secretions

Figure 17-4a External Features and Accessory Structures of the Eye.

Gross and superficial anatomy of the accessory structures. ATLAS: Plates 3c; 12a; 16a,b

17-3 Structures of the Eye (4 of 21)

Conjunctiva

Mucous membrane covered by an epithelium

Palpebral conjunctiva covers inner surface of eyelids

Bulbar conjunctiva covers anterior surface of eye

Extends to edges of cornea

Conjunctivitis (pinkeye)

Inflammation of conjunctiva

17-3 Structures of the Eye (5 of 21)

Lacrimal apparatus

Produces, distributes, and removes tears

Lacrimal gland (tear gland)

Produces tears that bathe conjunctival surfaces

Secretions contain lysozyme (antibacterial enzyme)

Fornix

Pocket where palpebral conjunctiva joins bulbar conjunctiva

Receives 10-12 ducts from lacrimal gland

17-3 Structures of the Eye (6 of 21)

Tears

Collect in lacrimal lake at medial angle of eye

Pass through

Lacrimal puncta (pores)

Lacrimal canaliculi (canals)

Lacrimal sac

Nasolacrimal duct

To nasal cavity

Figure 17-4b External Features and Accessory Structures of the Eye.

The organization of the lacrimal apparatus. ATLAS: Plates 3c; 12a; 16a,b

17-3 Structures of the Eye (7 of 21)

Layers of the wall of the eyeball

Outer fibrous layer

Intermediate vascular layer (uvea)

Deep inner layer (retina)

Orbital fat

Cushions and insulates each eye

17-3 Structures of the Eye (8 of 21)

Eyeball

Hollow

Filled with fluid

Two interior cavities

Small anterior cavity (contains aqueous humor)

Large posterior cavity (contains vitreous body)

Figure 17-5b The Sectional Anatomy of the Eye.

Horizontal section of right eye. ATLAS: Plates 12a; 16a,b

17-3 Structures of the Eye (9 of 21)

Fibrous layer (outermost layer of eyeball)

Sclera

White of the eye

Cornea

Transparent portion

Corneoscleral junction (corneal limbus)

Border between cornea and sclera

Figure 17-5a The Sectional Anatomy of the Eye.

Sagittal section of left eye. ATLAS: Plates 12a; 16a,b

17-3 Structures of the Eye (10 of 21)

Vascular layer (uvea)

Provides route for blood vessels and lymphatics that supply tissues of eye

Regulates amount of light entering eye

Secretes and reabsorbs aqueous humor that circulates within chambers of eye

Controls shape of lens, which is essential to focusing

Figure 17-5c The Sectional Anatomy of the Eye.

Superior view of dissection of right eye. ATLAS: Plates 12a; 16a,b

17-3 Structures of the Eye (11 of 21)

Vascular layer

Iris

Contains blood vessels, melanocytes, and two layers of smooth muscle (pupillary muscles)

Pupillary muscles

Change diameter of pupil (central opening of iris)

Figure 17-6 The Pupillary Muscles.

17-3 Structures of the Eye (12 of 21)

Vascular layer

Ciliary body

Attaches to iris

Extends posteriorly to level of ora serrata

Serrated anterior edge of neural layer of retina

Contains ciliary muscle and ciliary processes

Ciliary zonule (suspensory ligament)

Attaches lens to ciliary processes

17-3 Structures of the Eye (13 of 21)

Vascular layer

Choroid

Vascular layer that separates fibrous and inner layers posterior to ora serrata

Capillaries deliver oxygen and nutrients to retina

17-3 Structures of the Eye (14 of 21)

Inner layer (retina)

Pigmented layer

Absorbs light that passes through neural layer

Neural layer

Contains supporting cells and neurons

Outermost part contains photoreceptors

Rods and cones

17-3 Structures of the Eye (15 of 21)

Rods

Do not discriminate colors

Highly sensitive to light

Cones

Provide color vision

Densely clustered in macula

Especially in fovea centralis (fovea)

At center of macula

Site of sharpest color vision

Visual axis is the line from an object to fovea

Figure 17-7a The Organization of the Retina (Part 1 of 2).

The cellular organization of the retina. The photoreceptors are closer to the choroid than they are to the posterior cavity (vitreous chamber).

Figure 17-7a The Organization of the Retina (Part 2 of 2).

The cellular organization of the retina. The photoreceptors are closer to the choroid than they are to the posterior cavity (vitreous chamber).

Figure 17-7b The Organization of the Retina.

A photograph of the retina as seen through the pupil.

Figure 17-7c The Organization of the Retina.

The optic disc in diagrammatic sagittal section.

17-3 Structures of the Eye (16 of 21)

Neural layer

Bipolar cells

Synapse with rods and cones

Ganglion cells

Synapse with bipolar cells

Horizontal cells

Extend across neural layer

Amacrine cells

Comparable to horizontal cells

17-3 Structures of the Eye (17 of 21)

Horizontal and amacrine cells

Facilitate or inhibit communication between photoreceptors and ganglion cells

Alter sensitivity of retina

Optic disc

Circular region just medial to fovea

Origin of optic nerve

No photoreceptors (blind spot)

Figure 17-8 A Demonstration of the Presence of a Blind Spot.

Close your left eye and stare at the plus sign with your right eye, keeping the plus sign in the center of your field of vision. Begin with the page a few inches away from your eye, and gradually increase the distance. The dot will disappear when its image falls on the blind spot, at your optic disc. To check the blind spot in your left eye, close your right eye and repeat the sequence while you stare at the dot.

17-3 Structures of the Eye (18 of 21)

Chambers of the eye

Ciliary body and lens divide interior of eye into

Large posterior cavity

Smaller anterior cavity

Divided by iris into anterior and posterior chambers

17-3 Structures of the Eye (19 of 21)

Aqueous humor

Fluid that circulates within anterior cavity

Also diffuses through posterior cavity

Enters scleral venous sinus (canal of Schlemm) at corneoscleral junction

Reenters circulation at veins in sclera

Intra-ocular pressure

Fluid pressure in aqueous humor

Helps retain eye shape

Figure 17-9 The Circulation of Aqueous Humor.

Aqueous humor, which is secreted at the ciliary body, circulates through the posterior and anterior chambers before it is reabsorbed through the scleral venous sinus.

17-3 Structures of the Eye (20 of 21)

Vitreous body

Gelatinous mass in posterior cavity

Helps stabilize shape of eye

Vitreous humor

Fluid portion of vitreous body

17-3 Structures of the Eye (21 of 21)

Lens

Held in place by ciliary zonule

Lens fibers

Enucleate cells in interior of lens

Filled with crystallins, which provide clarity and focusing power

Cataracts

Loss of transparency in lens

Senile cataracts

Most common form; natural consequence of aging

17-4 Refraction and Focusing (1 of 3)

Learning Outcome: Describe how refraction and the focusing of light on the retina lead to vision.

Refraction and focusing of light

Light is refracted (bent) as it passes through cornea and lens

Focal point

Specific point of intersection of light rays on retina

Focal distance

Distance between center of lens and focal point

Figure 17-10 Factors Affecting Focal Distance.

Light rays from a source are refracted when they reach the lens of the eye. The rays are then focused onto a single focal point.

17-4 Refraction and Focusing (2 of 3)

Astigmatism

Condition where light passing through cornea and lens is not refracted properly

Visual image is distorted

Accommodation

Automatic adjustment of eye to provide clear vision

Lens becomes rounder to focus on nearby objects

Flatter lens allows focus on distant objects

Figure 17-11a Accommodation.

For close vision: Ciliary muscle contracted, lens rounded. For the eye to form a sharp image, the lens becomes rounder for close objects and flatter for distant objects.

Figure 17-11b Accommodation.

For distant vision: Ciliary muscle relaxed, lens flattened. For the eye to form a sharp image, the lens becomes rounder for close objects and flatter for distant objects.

17-4 Refraction and Focusing (3 of 3)

Image arriving at retina is miniaturized, upside down, and reversed from left to right

Brain compensates

Visual acuity

Clarity of vision

Standard rating is 20/20

Scotoma

Abnormal, permanent blind spot

May result from compression of optic nerve, damage to photoreceptors, or central damage

Figure 17-12a Image Formation.

Light from a point at the top of an object is focuse don the lower retinal surface. These illustrations are not drawn to scale because the fovea centralis occupies a small area of the retina, and the projected images are very tiny. As a result, the crossover of light rays is shown in the lens, but it actually occurs very close to the fovea centralis.

Figure 17-12b Image Formation.

Light from a point at the bottom of an object is focused on the upper retinal surface. These illustrations are not drawn to scale because the fovea centralis occupies a small area of the retina, and the projected images are very tiny. As a result, the crossover of light rays is shown in the lens, but it actually occurs very close to the fovea centralis.

Figure 17-12c Image Formation.

Light rays projected from a vertical object show why the image arrives upside down. (Note that the image is also reversed.) These illustrations are not drawn to scale because the fovea centralis occupies a small area of the retina, and the projected images are very tiny. As a result, the crossover of light rays is shown in the lens, but it actually occurs very close to the fovea centralis.

Figure 17-12d Image Formation.

Light rays projected from a horizontal object show why the mage arrives with a left and right reversal. The image also arrives upside down. These illustrations are not drawn to scale because the fovea centralis occupies a small area of the retina, and the projected images are very tiny. As a result, the crossover of light rays is shown in the lens, but it actually occurs very close to the fovea centralis.

Figure 17-13 Refractive Problems (Part 1 of 5).

Figure 17-13 Refractive Problems (Part 2 of 5).

Figure 17-13 Refractive Problems (Part 3 of 5).

Figure 17-13 Refractive Problems (Part 4 of 5).

Figure 17-13 Refractive Problems (Part 5 of 5).

17-5 Physiology of Vision (1 of 12)

Learning Outcome: Explain color and depth perception, describe how light stimulates the production of nerve impulses, and trace the visual pathways to their destinations in the brain.

Photoreceptors

Rods

Detect presence or absence of photons

Cones

Provide information about wavelengths of photons

Both rods and cones have

Inner segment containing major organelles

Outer segment with membranous discs

Contain visual pigments

17-5 Physiology of Vision (2 of 12)

Visual pigments

Absorb photons

First step in photoreception

Derivatives of rhodopsin

Opsin (protein) plus retinal (pigment)

Retinal is synthesized from vitamin A

Figure 17-14a Structure of Rods, Cones, and the Rhodopsin Molecule.

Structure of rods and cones

Figure 17-14b Structure of Rods, Cones, and the Rhodopsin Molecule.

Structure of rhodopsin molecule

17-5 Physiology of Vision (3 of 12)

Color vision

Provided by blue cones, green cones, and red cones

Each type has a different form of opsin

Color blindness

Inability to distinguish certain colors

Figure 17-15 Cone Types and Sensitivity to Color.

This graph compares the absorptive characteristics of blue, green, and red cones with those of typical rods.

Figure 17-18 A Standard Test for Color Vision.

People who lack one or more types of cones cannot see the number 12 in this pattern.

17-5 Physiology of Vision (4 of 12)

Steps in photoreception

Absorption of a photon changes retinal from 11-cis to 11-trans form

This activates opsin

Opsin activates transducin (G protein)

Which activates phosphodiesterase (PDE)

PDE reduces levels of cyclic GMP

Chemically gated sodium ion channels close

Dark current is reduced

Rate of neurotransmitter release declines

Figure 17-16 Photoreception (Part 3 of 6).

Figure 17-16 Photoreception (Part 4 of 6).

Figure 17-16 Photoreception (Part 5 of 6).

Figure 17-16 Photoreception (Part 6 of 6).

17-5 Physiology of Vision (5 of 12)

Recovery after stimulation

Bleaching

After absorbing a photon

Rhodopsin splits into retinal and opsin

11-trans retinal is converted back to 11-cis retinal

Requires ATP

Retinal then recombines with opsin

Night blindness (nyctalopia)

Results from deficiency of vitamin A

Figure 17-17 Bleaching and Regeneration of Visual Pigments.

17-5 Physiology of Vision (6 of 12)

Light and dark adaptation

Dark-adapted state

Visual pigments are fully receptive to stimulation

Light-adapted state

Rates of bleaching and reassembly of visual pigments are balanced

Retinitis pigmentosa (RP)

Inherited disease

Characterized by progressive retinal degeneration

17-5 Physiology of Vision (7 of 12)

Visual pathways

Begin at photoreceptors

End at visual cortex of cerebral hemispheres

Messages must cross two synapses before moving toward brain

Photoreceptor to bipolar cell

Bipolar cell to ganglion cell

17-5 Physiology of Vision (8 of 12)

Ganglion cells

Monitor specific portions of field of vision

M cells

Ganglion cells that monitor rods

Relatively large

Provide information about

General form of an object

Motion

Shadows in dim lighting

17-5 Physiology of Vision (9 of 12)

Ganglion cells

P cells

Ganglion cells that monitor cones

In fovea, ratio of cones to ganglion cells is 1:1

Smaller and more numerous than M cells

Provide information about

Edges

Fine detail

Color

17-5 Physiology of Vision (10 of 12)

Ganglion cells

On-center neurons

Excited by light arriving in center of receptive field

Inhibited when light strikes edges

Off-center neurons

Inhibited by light in central zone

Stimulated by light at edges

Figure 17-19 Convergence and Ganglion Cell Function.

Photoreceptors are organized in groups within a receptive field. Each ganglion cell monitors a well-defined portion of that field. Some ganglion cells (on-center neurons, labeled A) respond strongly to light arriving at the center of their receptive field. Others (off-center neurons, labeled B) respond most strongly to illumination of the edges of their receptive field.

17-5 Physiology of Vision (11 of 12)

Central processing of visual information

Axons from ganglion cells converge on optic disc

Penetrate wall of eye

Proceed toward diencephalon as optic nerve (II)

Two optic nerves reach diencephalon after partial crossover at optic chiasm

Information travels to visual cortex in occipital lobe

Optic radiation

Bundle of projection fibers linking lateral geniculates with visual cortex

17-5 Physiology of Vision (12 of 12)

Field of vision

Combined visual images from left and right eyes

Depth perception

Obtained by comparing relative positions of objects between images received from both eyes

Brainstem and visual processing

Circadian rhythm

Daily pattern of activity tied to day-night cycle

Established from visual information

Affects metabolic rate, blood pressure, etc.

Figure 17-20 The Visual Pathways.

The crossover of some nerve fibers occurs at the optic chiasm. As a result, each hemisphere receives visual information from the medial half of the field of vision of the eye on that side, and from the lateral half of the field of vision of the eye on the opposite side. Visual association areas integrate this information to develop a composite picture of the entire field of vision.

17-6 The Ear (1 of 26)

Learning Outcome: Describe the structures of the external, middle, and internal ear, explain their roles n equilibrium and hearing, and trace the pathways for equilibrium and hearing to their destinations in the brain.

Ear

External ear

Middle ear

Internal ear

Figure 17-21 The Anatomy of the Ear.

The dashed lines indicate the boundaries separating the three anatomical regions of the ear (external, middle, and internal).

17-6 The Ear (2 of 26)

External ear

Auricle (pinna)

Surrounds and protects external acoustic meatus (auditory canal)

Provides directional sensitivity

Tympanic membrane (eardrum)

Thin, semitransparent sheet

At end of external acoustic meatus

Separates external ear from middle ear

17-6 The Ear (3 of 26)

External ear

Ceruminous glands

Integumentary glands along external acoustic meatus

Secrete waxy material (cerumen)

Helps keep out foreign objects and insects

Slows growth of microorganisms

100

17-6 The Ear (4 of 26)

Middle ear (tympanic cavity)

Air-filled chamber

Communicates with nasopharynx through auditory tube

Permits equalization of pressure on either side of tympanic membrane

Contains three tiny ear bones (auditory ossicles)

Malleus (hammer)

Incus (anvil)

Stapes (stirrup)

101

Figure 17-22a The Middle Ear.

The structures of the middle ear

Figure 17-22b The Middle Ear.

The tympanic membrane and auditory ossicles

Figure 17-22c The Middle Ear.

The isolated auditory ossicles

17-6 The Ear (5 of 26)

When sound waves vibrate tympanic membrane

Auditory ossicles conduct vibrations to internal ear

Two small muscles protect the ear from very loud noises

Tensor tympani

Pulls on malleus and stiffens tympanic membrane

Stapedius

Reduces movement of stapes at oval window

105

17-6 The Ear (6 of 26)

Internal ear

Winding passageway (labyrinth)

Bony labyrinth surrounds and protects membranous labyrinth

Perilymph flows between the two labyrinths

Endolymph is within membranous labyrinth

Bony labyrinth can be subdivided into

Vestibule

Semicircular canals

Cochlea

106

Figure 17-23b The Internal Ear.

The bony and membranous labyrinths. Areas of the membranous labyrinth containing sensory receptors (ampullary crests, maculae, and spiral organ) are shown in purple.

Figure 17-23a The Internal Ear.

A section through one of the semicircular canals, showing the relationship between the bony and membranous labyrinths, and the boundaries of perilymph and endolymph.

17-6 The Ear (7 of 26)

Internal ear

Vestibule

Encloses saccule and utricle

Receptors detect gravity and linear acceleration

Three semicircular canals

Contain three semicircular ducts

Receptors stimulated by rotation of head

Cochlea

Contains cochlear duct of membranous labyrinth

Receptors provide sense of hearing

109

17-6 The Ear (8 of 26)

Internal ear

Round window

Thin, membranous partition

Separates perilymph from air spaces of middle ear

Oval window

Connected to base of stapes by collagen fibers

110

17-6 The Ear (9 of 26)

Equilibrium

State of physical balance

Sensations provided by receptors of vestibular complex (vestibule and semicircular canals)

Hair cells

Sensory receptors of internal ear

Provide information about direction and strength of mechanical stimuli

111

17-6 The Ear (10 of 26)

Anterior, posterior, and lateral semicircular ducts

Continuous with utricle

Each duct contains an expanded region (ampulla)

With gelatinous ampullary cupula

Ampullary crest contains hair cells

Each hair cell in vestibular complex has

80-100 stereocilia (resemble very long microvilli)

A single large kinocilium

112

Figure 17-24a The Semicircular Ducts.

An anterior view of the right semicircular ducts, the utricle, and the saccule, showing the locations of sensory receptors.

Figure 17-24b The Semicircular Ducts.

A cross section through the ampulla of a semicircular duct.

Figure 17-24c The Semicircular Ducts.

Endolymph movement along the length of the duct moves the ampullary cupula and stimulates the hair cells.

Figure 17-24d The Semicircular Ducts.

A representative hair cell (receptor) from the vestibular complex. Bending the sterocilia toward the kinocilium depolarizes the cell and stimulates the sensory neuron. Displacement in the opposite direction inhibits the sensory neuron.

17-6 The Ear (11 of 26)

Utricle and saccule

Hair cells provide sensations of position and linear movement

Connected with endolymphatic duct, which ends in endolymphatic sac

117

17-6 The Ear (12 of 26)

Utricle and saccule

Maculae

Oval structures where hair cells cluster

Macula of utricle senses horizontal movement

Macula of saccule senses vertical movement

Otoliths (“ear stones”)

Densely packed calcium carbonate crystals on surface of gelatinous mass

118

Figure 17-25a The Saccule and Utricle.

The location of the maculae

Figure 17-25b The Saccule and Utricle.

The structure of an individual macula of utricle

Figure 17-25c The Saccule and Utricle.

A diagram of the functioning of the macula of utricle when the head is held normally (1) and then tilted back (2).

17-6 The Ear (13 of 26)

Pathways for equilibrium sensations

Sensory neurons in vestibular ganglia

Monitor hair cells of vestibular complex

Fibers from ganglia form vestibular nerve of vestibulocochlear nerve (VIII)

Synapse within vestibular nuclei at boundary between pons and medulla oblongata

122

17-6 The Ear (14 of 26)

Four functions of vestibular nuclei

Integrate sensory information about balance and equilibrium from both sides of head

Relay information from vestibular complex to cerebellum

Relay information from vestibular complex to cerebral cortex

Providing conscious sense of head position

Send commands to motor nuclei in brainstem and spinal cord

123

Figure 17-26 Pathways for Equilibrium Sensations.

17-6 The Ear (15 of 26)

Reflexive motor commands from vestibular nuclei

Distributed to motor nuclei for cranial nerves involved with eye, head, and neck movements

Instructions descending in vestibulospinal tracts of spinal cord

Adjust peripheral muscle tone

Complement reflexive movements of head and neck

125

17-6 The Ear (16 of 26)

Automatic movements of eyes

Directed by superior colliculi of midbrain in response to sensations of motion

Attempt to keep gaze focused on a specific point

If spinning rapidly, eyes make jerky movements

Nystagmus

Trouble controlling eye movements when body is stationary

Caused by damage to brainstem or internal ear

126

17-6 The Ear (17 of 26)

Process of hearing

Sound waves are converted into mechanical movements by vibration of tympanic membrane

Auditory ossicles conduct vibrations to internal ear

Vibrations are converted to pressure waves in fluid

Detected by hair cells in cochlear duct

Information is sent to auditory cortex of brain

127

17-6 The Ear (18 of 26)

Introduction to sound

Pressure wave

Sine wave (S-shaped curve)

Consists of a region where air molecules are crowded together

And adjacent zone where they are farther apart

128

17-6 The Ear (19 of 26)

Pressure waves

Wavelength

Distance between two adjacent wave crests

Frequency

Number of waves (cycles) that pass a fixed reference point in a given time

Measured in hertz (Hz)

Number of cycles per second

129

17-6 The Ear (20 of 26)

Pressure wave

Pitch

Our sensory response to frequency

Amplitude

Height of a sound wave

Intensity

Amount of energy in a sound wave

Determines how loud it seems

Reported in decibels

130

Figure 17-27a The Nature of Sound.

Sound waves (here, generated by a tuning fork) travel through the air as pressure waves.

Figure 17-27b The Nature of Sound.

A graph showing the sound energy arriving at the tympanic membrane. The distance between wave peaks is the wavelength The number of waves arriving each second is the frequency, which we perceive as pitch. Frequencies are reported in cycles per second (cps), or hertz (Hz). The amount of energy carried by the wave is its amplitude. The greater the amplitude, the louder the sound.

Table 17-1 Intensity of Representative Sounds

17-6 The Ear (21 of 26)

Cochlear duct (scala media)

Lies between

Scala vestibuli (vestibular duct) and

Scala tympani (tympanic duct)

Hair cells lie in spiral organ (organ of Corti)

Rests on basilar membrane

Separates cochlear duct from scala tympani

Hair cells lack kinocilia

Stereocilia contact overlying tectorial membrane

134

Figure 17-28a The Cochlea.

The structure of the cochlea

Figure 17-28b The Cochlea (Part 1 of 2).

Diagrammatic and sectional views of the spiral-shaped cochlea

Figure 17-28b The Cochlea (Part 2 of 2).

Figure 17-29a The Spiral Organ.

A three-dimensional section of the cochlea, showing the compartments, tectorial membrane, and spiral organ

Figure 17-29b The Spiral Organ.

Sectional view of the cochlea and spiral organ

Figure 17-29c The Spiral Organ.

Diagram of the receptor hair cell complex of the spiral organ

17-6 The Ear (22 of 26)

Auditory discrimination

Range from softest to loudest tolerable sound represents trillion-fold increase in power

Young children have greatest hearing range

With age, damage accumulates

Tympanic membrane gets less flexible

Articulations between ossicles stiffen

Round window may begin to ossify

141

17-6 The Ear (23 of 26)

Six basic steps in process of hearing

Sound waves arrive at tympanic membrane

Movement of tympanic membrane displaces auditory ossicles

Movement of stapes at oval window produces pressure waves in perilymph of scala vestibuli

142

Figure 17-30 Sound and Hearing (Part 1 of 2).

Steps in the reception and transduction of sound energy.

17-6 The Ear (24 of 26)

Six basic steps in process of hearing

Pressure waves distort basilar membrane on their way to round window of scala tympani

Vibration of basilar membrane causes hair cells to vibrate against tectorial membrane

Information about stimulation is relayed to CNS over cochlear nerve

Spiral ganglion contains cell bodies of bipolar sensory neurons that monitor cochlear hair cells

144

Figure 17-30 Sound and Hearing (Part 2 of 2).

Steps in the reception and transduction of sound energy.

Figure 17-31a Frequency Discrimination.

The flexibility of the basilar membrane varies along its length, so pressure waves of different frequencies affect different parts of the membrane.

Figure 17-31b Frequency Discrimination.

The effects of a vibration of the stapes at a frequency of 6000 Hz. When the stapes moves inward, as shown here, the basilar membrane distorts toward the round window, which bulges into the cavity of the middle ear.

Figure 17-31c Frequency Discrimination.

When the stapes moves outward, as shown here, the basilar membrane rebounds and distorts toward the oval window.

17-6 The Ear (25 of 26)

Auditory pathways

Afferent fibers of sensory neurons in spiral ganglion form cochlear nerve

Axons enter medulla oblongata and synapse at cochlear nucleus

Information ascends to

Superior olivary nuclei of pons

Inferior colliculi of midbrain

Midbrain coordinates unconscious motor responses

149

17-6 The Ear (26 of 26)

Auditory pathways

Ascending auditory sensations synapse in medial geniculate body of thalamus

Projection fibers deliver information to auditory cortex of temporal lobe

150

Figure 17-32 Pathways for Auditory Sensations (Part 1 of 2).

Figure 17-32 Pathways for Auditory Sensations (Part 2 of 2).