Auditory and Vestibular systems

Question 1

what are the 2 divisions of CN VIII?

Answer 1

cochlear - sound and vestibular - head position and movement

Question 2

what does CN VIII innervate?

Answer 2

hair cells (mechanoreceptors)

Question 3

where are the auditory and vestibular structures embedded?

Answer 3

in the temporal bone

Question 4

where are the auditory and vestibular structures embedded?

Answer 4

in the temporal bone

Question 5

what is perilymph?

Answer 5

• fills bony labyrinth
• similar to CSF
• continuous with subarachnoid space thru cochlear aqueduct

Question 6

what is endolymph?

Answer 6

• fills membranous labyrinth

- similar to ICF

Question 7

what keeps the the perilymph and endolymph separate?

Answer 7

the tight junctions of hair cells

-establishes voltage and concentration gradients needed for transduction (because ion concentration difference)

Question 8

where is endolymph resorbed?

Answer 8

in the endolympathic sac

Question 9

what is menieres disease?

Answer 9

obstruction of the flow of endolymph leading to vertigo attacks, nausea and hearing loss
-once obstruction is relieved, the disease goes away

Question 10

what is menieres disease?

Answer 10

obstruction of the flow of endolymph leading to vertigo attacks, nausea and hearing loss
-once obstruction is relieved, the disease goes away

Question 11

what is a hair cell?

Answer 11

have specialized microvilli known as stereocilia arranged in rows from shortest to tallest

Question 12

what is the tallest stereocilia called?

Answer 12

kinocilium (embedded in gelatinous layer)

Question 13

where are kinocilium not found?

Answer 13

cochlear hair cells

Question 14

what causes the receptor potential to be transduced?

Answer 14

movement of the gelatin and deflection of stereocilia

Question 15

what depolarizes hair cells?

Answer 15

deflection towards the tallest stereocilia

Question 16

what hyperpolarizes hair cells?

Answer 16

deflection away from the tallest stereocilia

Question 17

what enables the amplification of sound from an airborne outer and middle ear to a fluid filled inner ear?

Answer 17

the tympanic membrane is 15X the size of the stapes (over the oval window) so the force is larger per unit area
-the middle ear basically amplifies the sound

Question 18

stapedius mm.

Answer 18

pulls the stapes away from the oval window, stiffening the ossicular chain, making it harder to move perilymph

• *blocks the sound of own voice
• innervated by CN VII

Question 19

tensor tympani mm.

Answer 19

pulls the malleus in towards the middle ear, away from the tympanic membrane, stiffening the ossicular chain, making it harder to move perilymph

• *blocks chewing noise and anticipates loud sounds
• innervated by CN V

Question 20

tensor tympani mm.

Answer 20

pulls the malleus in towards the middle ear, away from the tympanic membrane, stiffening the ossicular chain, making it harder to move perilymph

• *blocks chewing noise and anticipates loud sounds
• innervated by CN V

Question 21

what are the compartments within the cochlea?

Answer 21

scala vestibuli (perilymph), scala media (endolymph) and scala tympani (perilymph) that is continuous with the round window

Question 22

what is the modiolus?

Answer 22

spongy bone at the core of the cochlea that houses spiral ganglion

Question 23

what is spiral ganglion?

Answer 23

cell bodies of the primary afferent fibers that collect and form the cochlear division of CN VIII

Question 24

what are the compartments within the cochlea?

Answer 24

scala vestibuli (perilymph), scala media (endolymph considered the “duct” portion) and scala tympani (perilymph) that is continuous with the round window

Question 25

what is spiral ganglion?

Answer 25

cell bodies of the primary afferent fibers that collect and form the cochlear division of CN VIII

Question 26

where is endolymph made in the cochlea?

Answer 26

stria vascularis

Question 27

what separates endolymph from perilymph?

Answer 27

reissners membrane and basilar membrane

Question 28

what does the organ of corti sit on?

Answer 28

the basilar membrane

Question 29

explain the organ of corti organization

Answer 29

a strip of cells (on basilar membrane) that contains the inner hair cells (not attached to tectorial membrane) and outer hair cells (insert into tectorial membrane)

Question 30

explain the organ of corti organization

Answer 30

a strip of cells (on basilar membrane) that contains the inner hair cells (not attached to tectorial membrane) and outer hair cells (insert into tectorial membrane)

Question 31

explain the tonotopic organization of the auditory system

Answer 31

• stapes movement causes the pressure pulse in the scala vestibuli that leads to the basilar membrane
• since the mechanical properties of the basilar membrane differs along its length, the peak amplitude’s location depends on stimulus frequency

Question 32

explain the tonotopic organization of the auditory system

Answer 32

• stapes movement causes the pressure pulse in the scala vestibuli that leads to the basilar membrane deformation
• since the mechanical properties of the basilar membrane differs along its length, the peak amplitude’s location depends on stimulus frequency

Question 33

cochlear implant

Answer 33

• takes advantage of tonotopic organization
• used when hair endings are damaged but the rest of CN VIII is fine
• place electrodes in through the round window into scala tympani so they are at different locations along the basilar membrane
• electronics stimulate CN VIII endings and the CNS takes over

Question 34

CNS auditory processing

Answer 34

spiral ganglion send axons to hair cells and cochlear nucleus, from there their the cochlear nucleus sends axons bilaterally to the superior olivary nucleus (through the trapezoid to get contralateral), they then travel up the lateral lemniscus to the inferior colliculis where they will both go contralateral up the inferior brachium to medial geniculate of the thalamus to the auditory cortex

Question 35

CNS auditory processing

Answer 35

spiral ganglion send axons to hair cells and cochlear nucleus, from there their the cochlear nucleus sends axons bilaterally to the superior olivary nucleus (through the trapezoid to get contralateral), they then travel up the lateral lemniscus to the inferior colliculis where they will both go contralateral up the inferior brachium to medial geniculate of the thalamus to the auditory cortex

Question 36

primary auditory cortex

Answer 36

• transverse gyri of Heschl
• superior surface of the temporal lobe
• *gyri run mediolateral

Question 37

primary auditory cortex

Answer 37

• transverse gyri of Heschl
• superior surface of the temporal lobe
• *gyri run mediolateral

Question 38

sound localization

Answer 38

-takes place in the superior olivary nucleus

-

Question 39

sound localization

Answer 39

• takes place in the superior olivary nucleus (medial nucleus tells arrival time)
• sound from the left reaches left ear before it reaches the right ear

Question 40

sound localization

Answer 40

• takes place in the superior olivary nucleus (medial nucleus tells arrival time)
• sound from the left reaches left ear before it reaches the right ear

Question 41

audiogram

Answer 41

• plot date based on tones through a headphone (air conduction) and vibration (bone conduction)
• conductive hearing loss if process doesn’t allow sound to reach labyrinth (ear infection), uses outer, middle and inner ear
• sensorineural hearing loss if process causes hair cell damage, bone should bypass ear and go straight to labyrinth

Question 42

why does the vestibular system of CN VIII not transmit sound?

Answer 42

• round round window for fluid movement to protrude
• not tight and stretched like the cochlea
• the hair cell arrangement is different

Question 43

what do the semicircular ducts detect?

Answer 43

-angular acceleration

Question 44

describe the arrangement of the semicircular ducts

Answer 44

the are all 90 degrees from one another, each end of the ducts communicates with the utricle (ant and posterior have one of their ends fused), and one end of each duct has an ampulla that contains crista, which contains the hair cells

Question 45

what is the cupula?

Answer 45

the gelatinous mass that covers the crista and extends across the ampulla that the hair cells of the semicircular ducts insert. all of the kinocilia face in the same direction

Question 46

explain how the semicircular ducts detect movement

Answer 46

if there is rotation in an axis perpendicular to each respective canal, the endolymph lags behind due to inertia, deflecting the cupula, stimulating the hair cells to depolarize. if rotation is maintained (like tea cups in disney) then the endolymph will catch up, and when the movement stops the endolymph will contain to move and hyperpolarize

Question 47

explain how the semicircular ducts detect movement

Answer 47

if there is rotation in an axis perpendicular to each respective canal, the endolymph lags behind due to inertia, deflecting the cupula, stimulating the hair cells to depolarize. if rotation is maintained (like tea cups in disney) then the endolymph will catch up, and when the movement stops the endolymph will contain to move and hyperpolarize

Question 48

Utricle

Answer 48

contain a macula that is horizontal (stereocilia face up) and detects side-to-side and backward and forward movements

Question 49

saccule

Answer 49

contains a macula that is vertical (stereocilia lateral) and detects forward-backward and up-down movements

Question 50

explain the otolithic membrane

Answer 50

• it is the gelatinous membrane of the macula
• contains calcium carbonate crystals “ear stones”
• makes membrane denser than endolymph
• if the stones break off and roll around then vertigo ensues

Question 51

explain the otolithic membrane

Answer 51

• it is the gelatinous membrane of the macula
• contains calcium carbonate crystals “ear stones”
• makes membrane denser than endolymph
• if the stones break off and roll around then vertigo ensues

Question 52

projections from the vestibular “scarpa” ganglion go?

Answer 52

peripheral proceses to the synaptic endings on hair cells and the central processes are to vestibular nuclei in the rostral medullas and caudal pons and some to cerebellum

Question 53

where does input to the vestibular system go?

Answer 53

vestibular “scarpa” ganglion give peripheral processes to the synaptic endings on hair cells and the central processes are to vestibular nuclei in the rostral medulla and caudal pons
-cerebellum, spinal cord and contralateral nuclei also provide input

Question 54

where are inputs going?

Answer 54

to the 4 vestibular nuclei (each semicircular duct and macula has its own pattern of termination in specific nuceli)

Question 55

where does the vestibular system project?

Answer 55

-spinal cord, eye movement nuclei (CN III, IV and VI) and cerebellum, contralateral vestibular nuclei, thalamus (VPL) to cerebral cortex

Question 56

where does the vestibular system project?

Answer 56

-spinal cord, eye movement nuclei (CN III, IV and VI), cerebellum, contralateral vestibular nuclei, thalamus (VPL) to cerebral cortex to provide conscious awareness of movement in space and visceral nuclei in brainstem to adjust cardiovascular system for lying down to standing up and sea-sickness

Question 57

where does the vestibular system project?

Answer 57

-spinal cord, eye movement nuclei (CN III, IV and VI), cerebellum, contralateral vestibular nuclei, thalamus (VPL) to cerebral cortex to provide conscious awareness of movement in space and visceral nuclei in brainstem to adjust cardiovascular system for lying down to standing up and sea-sickness

Question 58

what tract are you using when you are playing “dizzy bat”

Answer 58

lateral vestibulospinal tract (down the lateral funiculus)

• *excitatory projections to ipsalateral antigravity muscles
• what you use when you miss a step and your body compensates for it

Question 59

explain what the medial vestibular spinal tract does

Answer 59

• short, bilateral, extends to cervical cord via the MLF

- stabilizes the head as we walk and coordinates head and eye movements

Question 60

whats VOR?

Answer 60

vestibuloocular reflex
**reflex to keep the image on the retina for clear vision
-retinal photoreceptors are slow so the vestibular system works to prevent images from moving off the retina
afferent limb: VIII (vestibular) and efferent limb: all eye mm. nn. (III, IV, VI) as well as interneuronal connections

Question 61

nystagmus

Answer 61

If VOR isn’t working to compensate for too fast head movements, very rapid eye movements happen. rapid in one direction and slow in another

Question 62

how does alcohol affect the vestibular system?

Answer 62

normally cupula density = endolymph density and gravity does not affect the cupula and semicircular ducts are not affected by gravity
but when ethanol leaves capillaries and goes into the cupula, the density decreases, compared to endolymph and gravity DOES affect the semicircular canals and cupula
**when blood alcohol increases eyes go in one direction and as you come down from being drunk they move in the opposite direction
***creates vertigo illusion because thinks head is moving when its actually just a head postion

Question 63

How are you aware of your sense of position?

Answer 63

vestibular, proprioceptive and visual systems are all working together to produce sense of orientation and movement
-if one is lost, the other two will make up for it

Question 64

what is Rombergs sign?

Answer 64

when a patient closes their eyes and they sway or lose their balance
-one of the three “sense of position factors” is not working and its usually vestibular