auditory and vestibular

Question 1

Review: laminar organization of the retina

Answer 1

inside out organization whereby light can pass through the cells, reflect off the back of the eye, and excite the rods and cones. R and C synapses onto bipolar cells, and to ganglion cells (with horizontal and amacrine cell input)

Question 2

Production of sound

Answer 2

these are variations in air pressure

alternating compressed and spaced out sound waves propagated by elastic medium (the hair) at ~340 m/s

ears must capture this mechanical energy, transmit to receptor organ, and transduce to electrical siganls for neural analysis

Question 3

comparison of auditory and visual pathways

Answer 3

auditory receptors in cochlea -> brain stem neurons -> mgn -> auditory cortex

photoreceptors in eye -> other retinal neurons -> LGN -> visual cortex

Question 4

gross anat. of ear

Answer 4

pinna, auditory canal (meatus), tympanic membrane, ossicles, and cochlea

Question 5

pinna

Answer 5

outer part of ear that’s right above the earlobe

helps collect sound from wide area

Question 6

auditory canal (meatus)

Answer 6

entrance to internal ear; conducts sound

Question 7

tympanic membrane

Answer 7

“eardrum”

separates the outer from inner ear

Question 8

ossicles

Answer 8

tiny bones transfer tympanic membrane reverberations to oval window

Question 9

cochlea

Answer 9

contains fluid that physically transduces the oval window reverberation into neuronal signals

Question 10

What is the pathway of sound waves through the ear?

Answer 10

sound wave moves the tympanic membrane
tympanic membrane moves ossicles
ossicles move membrane at oval window
motion at oval window moves fluid into cochlea
fluid into cochlea causes response in sensory neurons

Question 11

middle ear

Answer 11

malleus, incus, stapes, and eustachian tube

Question 12

malleus (the hammer)

Answer 12

attached to tymp. membrane, forms rigid connection to incus

Question 13

incus (anvil)

Answer 13

forms flexible connection to stapes

Question 14

stapes (the stirrups)

Answer 14

connects to oval window like piston

Question 15

eustachian tube

Answer 15

air inside is continuous with nasal cavity, although closed by a valve; pressure changes distend (inward or outward by the tymp membrane, causing pain)

Question 16

sound amplification

Answer 16

goes through tympanic membrane and middle ear because:

cochlea filled with fluid, not air

ossicles transmit sound waves v concentratedly (because oval window is small compared to tmp mem)

sound at oval window thus is ~20x more intense than at tmp membrane

Question 17

attenuatoin reflex

Answer 17

contains tensor tympani muscle and stapedius muscle

contraction increases rigidity of ossicles
may be to adapt the ear to continuous high intensity sound
may protect the inner ear, small delay though
activated when we speak so we don’t hear our own voices so loudly

Question 18

tensor tympani muscle

Answer 18

originates at the bone in the skull and inserts into the malleus

Question 19

stapedius muscle

Answer 19

originates at bone in skull and inserts onto stapes

Question 20

cochlear anatomy

Answer 20

roughly size of pea
three fluid-filled membranes: scala vestibuli, scala media, and scala tympani
reissner’s membrane separates vestibuli from media
organ of corti surmounts basilar membrane and contains hair cells covered by tectorial membrane

Question 21

basilar membrane of the cochlea

Answer 21

cochlea narrows from base to apex – however the basilar membrane widens from base to apex (by ~5x)
stiffness of basilar membrane decreases from base to apex (by ~100x)
flexible and bends in response to sound

Question 22

traveling wave in basilar membrane

Answer 22

when sound pushes footplate of stapes at oval window, perilymph is displaced in scala vestibuli AND endolymph is displaced at scala media

stapes can also pull at oval window and displace perilymph in opposing fashion

Question 23

basilar membrane of cochlea

Answer 23

similar to rope/extension cord/hose – high frequency waves dissipate quickly but low frequency waves propagate very far

response of bm establishes place code in which different locations of membrane are maximally deforced

Question 24

organ of corti

Answer 24

contains hair cells, rods of corti, and various supporting cells
hair cells - contain ~100 stereocilia that bend in response to sound and initiate the transduction of sound into neural signal
rods of corti span the reticular lamina and basilar membrane and provide structural support
stereocilia of outer hair cells extend through reticular lamina, into endolymph, and ends in tectorial membrane
stereocilia of inner hair cells extend through reticular lamina, into endolymph, but do not reach tectorial membrane

Question 25

compression

Answer 25

downward deflection

causes stereocilia to bend in and hyperpolarize

Question 26

rarefaction

Answer 26

upward deflection

stereocilia bend outwards and depolarize

Question 27

stereocilia bend

Answer 27

regulated by TRP (transient receptor potential) and TRPA1 channels (mediates mechanoelectrical transduction of noise

Question 28

outer hair cells

Answer 28

one spiral ganglion synapses into multiple

Question 29

inner hair cells

Answer 29

one spiral ganglion synapses onto one

Question 30

amplification by outer hair cells

Answer 30

amplifies the movement of basilar membrane

Question 31

mechanism of sound localization

Answer 31

horizontal localization = needs comparison of sounds reaching BOTH ears
vertical localization = one ear is sufficient
interaural time delay

Question 32

interaural time delay

Answer 32

sound from the right/.left will reach right/left ear first and there will be a delay to the other ear
doesn’t work well with continuous high frequency tone

Question 33

interaural intensity difference

Answer 33

due to head effectively casting sound shadow over opposite ear

Question 34

what are delay lines and neuronal sensitivity to interaural delay

Answer 34

monaural neurons and binaural neurons

Question 35

monaural neurons

Answer 35

respond to sound from one ear (cochlear nuclei)

Question 36

binaural neurons

Answer 36

respond to sound from both ears (superior olive nuclei and “above”)

Question 37

sound localization based on reflection from pinna

Answer 37

localization of sound in vertical plane heavily relies on pinna

Question 38

tonotopic organization

Answer 38

axons leaving MGN project to primary auditory cortex via internal capsule in array called acoustic radiation

Question 39

semicircular canals

Answer 39

part of vestibular system

used for detecting head roation

Question 40

otoliths

Answer 40

detects force of gravity, tils of head, and linear acceleration based on the calcium carbonate crystals inside it

Question 41

macular orientation

Answer 41

when the head is upright:
vertically orientated with saccule, horizontally orientated with utricle

mirror image orientation of saccule and utricle on both sides of head
with movement, hair cells on one side are excited and on opposite side are inhibited – allowing CNS to unambiguously interpret all possible linear movements

Question 42

ampula and semicircular canal

Answer 42

cilia of hair cells extend into gelatinous cupula
cupula is bathed in endolymph
when canal rotates, endolymph lags behind and applies force to cupula in opposite direction

Question 43

push-pull activation of semicircular canals

Answer 43

head rotation causes excitation of hair cells in one horizontal semicircular canal and inhibition of hair cells in other
figure here shows that long lasting head rotation leads to adaptation of firing in vestibular axons
when rotation is stopped, vestibular axons from each side begins firing again, but with opposite patterns of excitation and inhibition

Question 44

presbyacusis

Answer 44

hearing loss due to physiologic process of aging
can be due to degeneration of cochlear hairs + supporting cells; thickening of basilar membrane; degen of neurons; changes in auditory cortex/processing