PPT Notes Chapter 13

Question 1

Structure of a Nerve

Answer 1

Cordlike organ of the PNS
Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue
Connective tissue coverings include:
Endoneurium—loose connective tissue that encloses axons and their myelin sheaths
Perineurium—coarse connective tissue that bundles fibers into fascicles
Epineurium—tough fibrous sheath around a nerve

Question 2

Classification of Nerves

Answer 2

Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers
Pure sensory (afferent) or motor (efferent) nerves are rare
Types of fibers in mixed nerves:
Somatic afferent and somatic efferent
Visceral afferent and visceral efferent
Peripheral nerves classified as cranial or spinal nerves

Question 3

Ganglia

Answer 3

Contain neuron cell bodies associated with nerves
Dorsal root ganglia (sensory, somatic) (Chapter12)
Autonomic ganglia (motor, visceral) (Chapter14)

Question 4

Regeneration of Nerve Fibers

Answer 4

Mature neurons are amitotic
If the soma of a damaged nerve is intact, axon will regenerate
Involves coordinated activity among:
Macrophages—remove debris
Schwann cells—form regeneration tube and secrete growth factors
Axons—regenerate damaged part
CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration [ALS involvement]

Question 5

Cranial Nerves

Answer 5

Twelve pairs of nerves associated with the brain
Most are mixed in function; two pairs are purely sensory
Each nerve is identified by a number (Ithrough XII) and a name

Question 6

I: The Olfactory Nerves

Answer 6

Arise from the olfactory receptor cells of nasal cavity
Pass through the cribriform plate of the ethmoid bone
Fibers synapse in the olfactory bulbs
Pathway terminates in the primary olfactory cortex
Purely sensory (olfactory) function

Question 7

II: The Optic Nerves

Answer 7

Arise from the retinas
Pass through the optic canals, converge and partially cross over at the optic chiasma
Optic tracts continue to the thalamus, where they synapse
Optic radiation fibers run to the occipital (visual) cortex
Purely sensory (visual) function

Question 8

III: The Oculomotor Nerves

Answer 8

Fibers extend from the ventral midbrain through the superior orbital fissures to the extrinsic eye muscles
Functions in raising the eyelid, directing the eyeball, constricting the iris (parasympathetic), and controlling lens shape

Question 9

IV: The Trochlear Nerves

Answer 9

Fibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle
Primarily a motor nerve that directs the eyeball

Question 10

V: The Trigeminal Nerves

Answer 10

Largest cranial nerves; fibers extend from pons to face
Three divisions
Ophthalmic (V1) passes through the superior orbital fissure
Maxillary (V2) passes through the foramen rotundum
Mandibular (V3) passes through the foramen ovale
Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

Question 11

VI: The Abducens Nerves

Answer 11

Fibers from the inferior pons enter the orbits via the superior orbital fissures
Primarily a motor, innervating the lateral rectus muscle

Question 12

VII: The Facial Nerves

Answer 12

Fibers from the pons travel through the internal acoustic meatuses, and emerge through the stylomastoid foramina to the lateral aspect of the face
Chief motor nerves of the face with 5 major branches
Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands
Sensory function (taste) from the anterior two-thirds of the tongue

Question 13

VIII: The Vestibulocochlear Nerves

Answer 13

Afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla border
Mostly sensory function; small motor component for adjustment of sensitivity of receptors

Question 14

IX: The Glossopharyngeal Nerves

Answer 14

Fibers from the medulla leave the skull via the jugular foramen and run to the throat
Motor functions: innervate part of the tongue and pharynx for swallowing, and provide parasympathetic fibers to the parotid salivary glands
Sensory functions: fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors

Question 15

X: The Vagus Nerves

Answer 15

The only cranial nerves that extend beyond the head and neck region
Fibers from the medulla exit the skull via the jugular foramen
Most motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal viscera
Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx

Question 16

XI: The Accessory Nerves

Answer 16

Formed from ventral rootlets from the C1–C5 region of the spinal cord (not the brain)
Rootlets pass into the cranium via each foramen magnum
Accessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid muscles

Question 17

XII: The Hypoglossal Nerves

Answer 17

Fibers from the medulla exit the skull via the hypoglossal canal
Innervate extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speech

Question 18

The Eye and Vision

Answer 18

70% of all sensory receptors are in the eye
Nearly half of the cerebral cortex is involved in processing visual information!
Most of the eye is protected by a cushion of fat and the bony orbit

Question 19

Accessory Structures of the Eye

Answer 19

Protect the eye and aid eye function
Eyebrows
Eyelids (palpebrae)
Conjunctiva
Lacrimal apparatus
Extrinsic eye muscles

Question 20

Eyebrows

Answer 20

Overlie the supraorbital margins
Function in
Shading the eye
Preventing perspiration from reaching the eye

Question 21

Eyelids

Answer 21

Protect the eye anteriorly
Palpebral fissure—separates eyelids
Lacrimal caruncle—elevation at medial commissure; contains oil and sweat glands
Tarsal plates—internal supporting connective tissue sheet
Levator palpebrae superioris—gives the upper eyelid mobility

Eyelashes
Nerve endings of follicles initiate reflex blinking
Lubricating glands associated with the eyelids
Tarsal (Meibomian) glands
Sebaceous glands associated with follicles
Ciliary glands between the hair follicles

Question 22

Conjunctiva

Answer 22

Transparent membrane
Palpebral conjunctiva lines the eyelids
Bulbar conjunctiva covers the white of the eyes
Produces a lubricating mucous secretion

Question 23

Lacrimal Apparatus

Answer 23

Lacrimal gland and ducts that connect to nasal cavity
Lacrimal secretion (tears)
Dilute saline solution containing mucus, antibodies, and lysozyme
Blinking spreads the tears toward the medial commissure
Tears enter paired lacrimal canaliculi via the lacrimal puncta
Drain into the nasolacrimal duct

Question 24

Extrinsic Eye Muscles

Answer 24

Six straplike extrinsic eye muscles
Originate from the bony orbit
Enable the eye to follow moving objects
Maintain the shape of the eyeball
Four rectus muscles originate from the common tendinous ring; names indicate the movements they promote
Two oblique muscles move the eye in the vertical plane and rotate the eyeball

Question 25

Structure of the Eyeball

Answer 25

Wall of eyeball contains three layers Fibrous Vascular Sensory Internal cavity is filled with fluids called humors [aqueous, vitreous] The lens separates the internal cavity into anterior and posterior segments (cavities)

Question 26

Fibrous Layer

Answer 26

Outermost layer; dense avascular connective tissue Two regions: sclera and cornea Sclera Opaque posterior region Protects and shapes eyeball Anchors extrinsic eye muscles Cornea: Transparent anterior 1/6 of fibrous layer Bends light as it enters the eye Sodium pumps of the corneal endothelium on the inner face help maintain the clarity of the cornea Numerous pain receptors contribute to blinking and tearing reflexes

Question 27

Vascular Layer (Uvea)

Answer 27

Middle pigmented layer Three regions: choroid, ciliary body, and iris Choroid region Posterior portion of the uvea Supplies blood to all layers of the eyeball Brown pigment absorbs light to prevent visual confusion Ciliary body Ring of tissue surrounding the lens Smooth muscle bundles (ciliary muscles) control lens shape Capillaries of ciliary processes secrete fluid into the anterior segment. Ciliary zonule (suspensory ligament) holds lens in position Iris The colored part of the eye Pupil—central opening that regulates the amount of light entering the eye Close vision and bright light—sphincter pupillae (circular muscles) contract; pupils constrict Distant vision and dim light—dilator pupillae (radial muscles) contract; pupils dilate Changes in emotional state—pupils dilate when the subject matter is appealing or requires problem-solving skills

Question 28

Sensory Layer: Retina

Answer 28

Delicate two-layered membrane Pigmented layer Outer layer Absorbs light and prevents its scattering Stores vitamin A for use by photoreceptor cells Neural layer Photoreceptor: transduce light energy Cells that transmit and process signals: bipolar cells, ganglion cells, amacrine cells, and horizontal cells

Question 29

The Retina

Answer 29

Ganglion cell axons Run along the inner surface of the retina Leave the eye as the optic nerve Optic disc (blind spot) Site where the optic nerve leaves the eye Lacks photoreceptors

Question 30

Photoreceptors

Answer 30

Rods More numerous at peripheral region of retina, away from the macula lutea Operate in dim light Provide indistinct, fuzzy, non color peripheral vision Cones Found in the macula lutea; concentrated in the fovea centralis Operate in bright light Provide high-acuity color vision

Question 31

Blood Supply to the Retina

Answer 31

Two sources of blood supply Choroid supplies the outer third (photoreceptors) Central artery and vein of the retina supply the inner two-thirds

Question 32

Internal Chambers and Fluids

Answer 32

The lens and ciliary zonule separate the anterior and posterior segments Posterior segment contains vitreous humor that: Transmits light Supports the posterior surface of the lens Holds the neural retina firmly against the pigmented layer Contributes to intraocular pressure Anterior segment is composed of two chambers Anterior chamber—between the cornea and the iris Posterior chamber—between the iris and the lens Anterior segment contains aqueous humor Plasma like fluid continuously filtered from capillaries of the ciliary processes Drains via the scleral venous sinus (canal of Schlemm) at the sclera-cornea junction Supplies nutrients and oxygen mainly to the lens and cornea but also to the retina, and removes wastes Glaucoma: compression of the retina and optic nerve if drainage of aqueous humor is blocked

Question 33

Lens

Answer 33

Biconvex, transparent, flexible, elastic, and avascular Allows precise focusing of light on the retina Cells of lens epithelium differentiate into lens fibers that form the bulk of the lens Lens fibers—cells filled with the transparent protein crystallin Lens becomes denser, more convex, and less elastic with age Cataracts (clouding of lens) occur as a consequence of aging, diabetes mellitus, heavy smoking, and frequent exposure to intense sunlight

Question 34

Light

Answer 34

Our eyes respond to visible light, a small portion of the electromagnetic spectrum Light: packets of energy called photons (quanta) that travel in a wavelike fashion Rods and cones respond to different wavelengths of the visible spectrum

Question 35

Refraction and Lenses

Answer 35

Refraction Bending of a light ray due to change in speed when light passes from one transparent medium to another Occurs when light meets the surface of a different medium at an oblique angle Light passing through a convex lens (as in the eye) is bent so that the rays converge at a focal point The image formed at the focal point is upside-down and reversed right to left

Question 36

Focusing Light on the Retina

Answer 36

Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, neural layer of retina, photoreceptors Light is refracted At the cornea Entering the lens Leaving the lens Change in lens curvature allows for fine focusing of an image

Question 37

Focusing for Distant Vision

Answer 37

Light rays from distant objects are nearly parallel at the eye and need little refraction beyond what occurs in the at-rest eye Far point of vision: the distance beyond which no change in lens shape is needed for focusing; 20 feet for emmetropic (normal) eye Ciliary muscles are relaxed Lens is stretched flat by tension in the ciliary zonule

Question 38

Focusing for Close Vision

Answer 38

Light from a close object diverges as it approaches the eye; requires that the eye make active adjustments Close vision requires Accommodation—changing the lens shape by ciliary muscles to increase refractory power Near point of vision is determined by the maximum bulge the lens can achieve Presbyopia—loss of accommodation over age 50 Constriction—the accommodation pupillary reflex constricts the pupils to prevent the most divergent light rays from entering the eye Convergence—medial rotation of the eyeballs toward the object being viewed

Question 39

Problems of Refraction

Answer 39

Myopia (nearsightedness)—focal point is in front of the retina, e.g. in a longer than normal eyeball Corrected with a concave lens Hyperopia (farsightedness)—focal point is behind the retina, e.g. in a shorter than normal eyeball Corrected with a convex lens Astigmatism—caused by unequal curvatures in different parts of the cornea or lens Corrected with cylindrically ground lenses, corneal implants, or laser procedures

Question 40

Functional Anatomy of Photoreceptors

Answer 40

Rods and cones Outer segment of each contains visual pigments (photopigments)—molecules that change shape as they absorb light Inner segment of each joins the cell body

Question 41

Rods

Answer 41

Functional characteristics Very sensitive to dim light Best suited for night vision and peripheral vision Perceived input is in gray tones only Pathways converge, where as many as 100 rods feed one ganglion cell, resulting in fuzzy and indistinct images

Question 42

Cones

Answer 42

Functional characteristics Need bright light for activation (have low sensitivity) Have one of three pigments that furnish a vividly colored view Nonconverging pathways, by virtue of each cone cell having its own “personal” bipolar cell, result in detailed, high-resolution vision

Question 43

Excitation of Cones

Answer 43

Method of excitation is similar to that of rods There are three types of cones, named for the colors of light absorbed: blue, green, and red Intermediate hues are perceived by activation of more than one type of cone at the same time Color blindness is due to a congenital lack of one or more of the cone types

Question 44

Signal Transmission in the Retina

Answer 44

Photoreceptors and bipolar cells only generate graded potentials (EPSPs and IPSPs) Light hyperpolarizes photoreceptor cells, causing them to stop releasing the inhibitory neurotransmitter glutamate Bipolar cells (no longer inhibited) are then allowed to depolarize and release neurotransmitter onto ganglion cells Ganglion cells generate APs that are transmitted in the optic nerve

Question 45

Light Adaptation

Answer 45

Occurs when moving from darkness into bright light Large amounts of pigments are broken down instantaneously, producing glare Pupils constrict Dramatic changes in retinal sensitivity: rod function ceases Cones and neurons rapidly adapt Visual acuity improves over 5–10 minutes

Question 46

Dark Adaptation

Answer 46

Occurs when moving from bright light into darkness The reverse of light adaptation Cones stop functioning in low-intensity light Pupils dilate Rhodopsin accumulates in the dark and retinal sensitivity increases within 20–30 minutes

Question 47

Visual Pathway

Answer 47

Axons of retinal ganglion cells form the optic nerve Medial fibers of the optic nerve decussate at the optic chiasma Most fibers of the optic tracts continue to the lateral geniculate body of the thalamus The optic radiation fibers connect to the primary visual cortex in the occipital lobes Other optic tract fibers send branches to the midbrain, ending in superior colliculi (initiating visual reflexes)

Question 48

Depth Perception

Answer 48

``` Both eyes view the same image from slightly different angles Depth perception (three-dimensional vision) results from cortical fusion of the slightly different images ```

Question 49

Retinal Processing

Answer 49

Several different types of ganglion cells are arranged in doughnut-shaped receptive fields On-center fields Stimulated by light hitting the center of the field Inhibited by light hitting the periphery of the field Off-center fields have the opposite effects These responses are due to different receptor types for glutamate in the “on” and “off” fields

Question 50

Thalamic Processing

Answer 50

Lateral geniculate nuclei of the thalamus Relay information on movement Segregate the retinal axons in preparation for depth perception Emphasize visual inputs from regions of high cone density Sharpen contrast information

Question 51

Cortical Processing

Answer 51

Two areas in the visual cortex Striate cortex (primary visual cortex) Processes contrast information and object orientation Prestriate cortices (visual association areas) Processes form, color, and motion input from striate cortex Complex visual processing extends into other regions Temporal lobe—processes identification of objects Parietal cortex and postcentral gyrus—process spatial location

Question 52

Chemical Senses

Answer 52

Taste and smell (olfaction) The chemoreceptors respond to chemicals in aqueous solution May be inhaled vapors

Question 53

Sense of Smell

Answer 53

The organ of smell—olfactory epithelium in the roof of the nasal cavity Olfactory receptor cells—bipolar neurons with radiating olfactory cilia Bundles of axons of olfactory receptor cells form the filaments of the olfactory nerve (cranial nerve I) Supporting cells surround and cushion olfactory receptor cells Basal cells lie at the base of the epithelium

Question 54

Physiology of Smell

Answer 54

Dissolved odorants bind to receptor proteins in the olfactory cilium membranes A G protein mechanism is activated, which produces cAMP as a second messenger cAMP opens Na+ and Ca2+ channels, causing depolarization of the receptor membrane that then triggers an action potential

Question 55

Olfactory Pathway

Answer 55

Olfactory receptor cells synapse with mitral cells in glomeruli of the olfactory bulbs Mitral cells amplify, refine, and relay signals along the olfactory tracts to the: Olfactory cortex Hypothalamus, amygdala, and limbic system

Question 56

Sense of Taste

Answer 56

Receptor organs are taste buds Found on the tongue On the tops of fungiform papillae On the side walls of foliate papillae and circumvallate (vallate) papillae

Question 57

Structure of a Taste Bud

Answer 57

``` Flask shaped 50–100 epithelial cells: Basal cells—dynamic stem cells Gustatory cells—taste cells Microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium ```

Question 58

Taste Sensations

Answer 58

There are five basic taste sensations Sweet—sugars, saccharin, alcohol, and some amino acids Sour—hydrogen ions Salt—metal ions Bitter—alkaloids such as quinine and nicotine Umami—amino acids glutamate and aspartate

Question 59

Physiology of Taste

Answer 59

In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical (tastant) Depolarizes the taste cell membrane, causing release of neurotransmitter Initiates a generator potential that elicits an action potential

Question 60

Taste Transduction

Answer 60

The stimulus energy of taste causes gustatory cell depolarization by: Na+ influx in salty tastes (directly causes depolarization) H+ in sour tastes (by opening cation channels) G protein gustducin in sweet, bitter, and umami tastes (leads to release of Ca2+ from intracellular stores, which causes opening of cation channels in the plasma membrane)

Question 61

Gustatory Pathway

Answer 61

Cranial nerves VII and IX [facial and glossopharyngeal] carry impulses from taste buds to the solitary nucleus of the medulla Impulses then travel to the thalamus and from there fibers branch to the: Gustatory cortex in the insula Hypothalamus and limbic system (appreciation of taste)

Question 62

Influence of Other Sensations on Taste

Answer 62

Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastes Temperature and texture enhance or detract from taste

Question 63

The Ear: Hearing and Balance

Answer 63

``` Three parts of the ear External (outer) ear Middle ear (tympanic cavity) Internal (inner) ear External ear and middle ear are involved with hearing Internal ear (labyrinth) functions in both hearing and equilibrium Receptors for hearing and balance Respond to separate stimuli Are activated independently ```

Question 64

External Ear

Answer 64

The auricle (pinna) is composed of: Helix (rim) Lobule (earlobe) External acoustic meatus (auditory canal) Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands Tympanic membrane (eardrum) Boundary between external and middle ears Connective tissue membrane that vibrates in response to sound Transfers sound energy to the bones of the middle ear

Question 65

Middle Ear

Answer 65

A small, air-filled, mucosa-lined cavity in the temporal bone Flanked laterally by the eardrum Flanked medially by bony wall containing the oval (vestibular) and round (cochlear) windows Epitympanic recess—superior portion of the middle ear Pharyngotympanic (auditory) tube—connects the middle ear to the nasopharynx Equalizes pressure in the middle ear cavity with the external air pressure

Question 66

Ear Ossicles

Answer 66

Three small bones in tympanic cavity: the malleus, incus, and stapes Suspended by ligaments and joined by synovial joints Transmit vibratory motion of the eardrum to the oval window Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to the hearing receptors

Question 67

Internal Ear

Answer 67

Bony labyrinth Tortuous channels in the temporal bone Three parts: vestibule, semicircular canals, and cochlea Filled with perilymph Series of membranous sacs [membranous labyrinth] within the bony labyrinth Filled with a potassium-rich endolymph

Question 68

Vestibule

Answer 68

Central egg-shaped cavity of the bony labyrinth Contains two membranous sacs Saccule is continuous with the cochlear duct Utricle is continuous with the semicircular canals These sacs House equilibrium receptor regions (maculae) Respond to gravity and changes in the position of the head

Question 69

Semicircular Canals

Answer 69

Three canals (anterior, lateral, and posterior) that each define two-thirds of a circle Membranous semicircular ducts line each canal and communicate with the utricle Ampulla of each canal houses equilibrium receptor region called the crista ampullaris Receptors respond to angular (rotational) movements of the head

Question 70

The Cochlea

Answer 70

A spiral, conical, bony chamber Extends from the vestibule Coils around a bony pillar Contains the cochlear duct, which houses the spiral organ (of Corti) and ends at the cochlear apex The cavity of the cochlea is divided into three chambers Scala vestibuli—abuts the oval window, contains perilymph Scala media (cochlear duct)—contains endolymph Scala tympani—terminates at the round window; contains perilymph The scalae tympani and vestibuli are continuous with each other at the helicotrema (apex) The “roof” of the cochlear duct is the vestibular membrane The “floor” of the cochlear duct is composed of: The bony spiral lamina The basilar membrane, which supports the organ of Corti The cochlear branch of nerve VIII runs from the organ of Corti to the brain

Question 71

Properties of Sound

Answer 71

Sound is A pressure disturbance (alternating areas of high and low pressure) produced by a vibrating object A sound wave Moves outward in all directions Is illustrated as an S-shaped curve or sine wave Pitch Perception of different frequencies Normal range is from 20–20,000 Hz The higher the frequency, the higher the pitch Loudness Subjective interpretation of sound intensity Normal range is 0–120 decibels (dB)

Question 72

Properties of Sound Waves

Answer 72

Frequency The number of waves that pass a given point in a given time Wavelength The distance between two consecutive crests Amplitude The height of the crests

Question 73

Transmission of Sound to the Internal Ear

Answer 73

Sound waves vibrate the tympanic membrane Ossicles vibrate and amplify the pressure at the oval window Pressure waves move through perilymph of the scala vestibuli Waves with frequencies below the threshold of hearing travel through the helicotrema and scali tympani to the round window Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane at a specific location, according to the frequency of the sound

Question 74

Resonance of the Basilar Membrane

Answer 74

Fibers that span the width of the basilar membrane are short and stiff near oval window, and resonate in response to high-frequency pressure waves. Longer fibers near the apex resonate with lower-frequency pressure waves

Question 75

Excitation of Hair Cells in the Spiral Organ

Answer 75

Cells of the spiral organ Supporting cells Cochlear hair cells One row of inner hair cells Three rows of outer hair cells Afferent fibers of the cochlear nerve coil about the bases of hair cells The stereocilia Protrude into the endolymph Enmeshed in the gel-like tectorial membrane Bending stereocilia Opens mechanically gated ion channels Inward K+ and Ca2+ current causes a graded potential and the release of neurotransmitter glutamate Cochlear fibers transmit impulses to the brain

Question 76

Auditory Pathways to the Brain

Answer 76

Impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei of the medulla From there, impulses are sent to the Superior olivary nucleus at the junction of the medulla and pons Inferior colliculus (auditory reflex center in the midbrain) From there, impulses pass to the auditory cortex via the thalamus Auditory pathways decussate so that both cortices receive input from both ears

Question 77

Auditory Processing

Answer 77

Impulses from specific hair cells are interpreted as specific pitches Loudness is detected by increased numbers of action potentials that result when the hair cells experience larger deflections Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears

Question 78

Homeostatic Imbalances of Hearing

Answer 78

Conduction deafness Blocked sound conduction to the fluids of the internal ear Can result from impacted earwax, perforated eardrum, or otosclerosis of the ossicles Sensorineural deafness Damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells Tinnitus: ringing or clicking sound in the ears in the absence of auditory stimuli Due to cochlear nerve degeneration, inflammation of middle or internal ears, side effects of aspirin Meniere’s syndrome: labyrinth disorder that affects the cochlea and the semicircular canals Causes vertigo, nausea, and vomiting

Question 79

Equilibrium and Orientation

Answer 79

Vestibular apparatus consists of the equilibrium receptors in the semicircular canals and vestibule Vestibular receptors monitor static equilibrium Semicircular canal receptors monitor dynamic equilibrium

Question 80

Maculae

Answer 80

Sensory receptors for static equilibrium One in each saccule wall and one in each utricle wall Monitor the position of the head in space, necessary for control of posture Respond to linear acceleration forces, but not rotation Contain supporting cells and hair cells Stereocilia and kinocilia are embedded in the otolithic membrane studded with otoliths (tiny CaCO3 stones) Maculae in the utricle respond to horizontal movements and tilting the head side to side Maculae in the saccule respond to vertical movements

Question 81

Activating Maculae Receptors

Answer 81

Bending of hairs in the direction of the kinocilia Depolarizes hair cells Increases the amount of neurotransmitter release and increases the frequency of action potentials generated in the vestibular nerve Bending in the opposite direction Hyperpolarizes vestibular nerve fibers Reduces the rate of impulse generation Thus the brain is informed of the changing position of the head

Question 82

Crista Ampullaris (Crista)

Answer 82

Sensory receptor for dynamic equilibrium One in the ampulla of each semicircular canal Major stimuli are rotatory movements Each crista has support cells and hair cells that extend into a gel-like mass called the cupula Dendrites of vestibular nerve fibers encircle the base of the hair cells

Question 83

Activating Crista Ampullaris Receptors

Answer 83

Cristae respond to changes in velocity of rotatory movements of the head Bending of hairs in the cristae causes Depolarizations, and rapid impulses reach the brain at a faster rate Bending of hairs in the opposite direction causes Hyperpolarizations, and fewer impulses reach the brain Thus the brain is informed of rotational movements of the head