W8 - Auditory/Vestibular

second half

the auditory system responds ___x faster than the visual system

1000

what is hearing

the process by which sound waves are transmitted to the brain via the ear and cochlea

what are the 4 purposes of hearing

communication, spatial awareness, interaction with environment, safety

what is the sound range that humans can detect

20Hz - 20kHz

what are the 3 bones of the middle eat

malleus, incus, stapes

which end of the cochlea is narrower

apical

____ and ___ interact via cochlear hair cells to generate __ signals

tectorial membrane, basilar membrane, mechanoelectrical

where are cochlear hair cells located

embedded in the basilar membrane

as vibrations travel through the fluid of the cochlea, the ___ shifts, moving the __

tectorial membrane, stereocilia

what are stereocilia

protrusions on the end of cochlear hair cells

what happens when the stereocilia are deflected?

release of neurotransmitter onto the auditory nerve

___% of the fibers of the auditory nerve come from _____

95, inner hair cells

there are __ row(s) of inner hair cells and _ row(s) of outer hair cells in the cochlea

1, 3

what is the function of the outer hair cells

receive efferent information from the CNS to modify the stiffness of the tectorial membrane in response to over and under stimulation

what is the set-up of stereocilia

made up of actin cytoskeleton, arranged shortest to tallest, connected to each other via tip links

if the stereocilia are deflected (away from/towards) the tallest stereocilium, the hair cell releases more neurotransmitter; if they are deflected (away from/towards) the tallest stereocilium, the hair cell releases less neurotransmitter.

towards, away from

what do the tip links do?

open mechanoelectrical transduction channels when stretched to allow inpouring of ions to then release neurotransmitters and cause an AP in the nerve fiber

what is tonotopy

the spatial organization of the basilar membrane responding to different frequencies of sound

lower pitched sounds are located towards the ____ end of the cochlea, while higher pitched sounds are located towards the __ end.

apical, basilar

how is tonotopy preserved from cochlea to CNS?

labeled line coding

what structure helps us decide where a sound is coming from

coincidence detection neurons

where are coincidence detection neurons located

medial superior olivary complex

why is it important to localize sound?

to center in on targets for motor action

explain how sound localization occurs for a sound coming from the left side of your head

the sound hits the left ear first, so the left ear sends an AP down the cochlear nerve towards the MSO. once the sound hits the right ear, the right cochlear nerve fires an AP. because the L nerve had a longer time to send the signal, the L AP reaches an MSO neuron further away from its side than the R AP does. The neuron that they converge on will respond the most strongly, and based on how far from L or R it is, the MSO can tell which side of the body the sound is on.

what is the purpose of the dorsal cochlear nucleus pathway

higher-order processing of sound, the “what”

what is the purpose of the ventral cochlear nucleus pathway

sound localization, the “where”

where are coincidence detection neurons located

superior olivary nucleus complex

the vestibular system has a _ _ _ _ which allows us to detect _ _

high baseline firing rate, the negative

what 3 things does the vestibular system detect relative to gravity?

self-motion, head position, spatial orientation

what are the 2 otolith organs?

utricle and saccule

the ___ detects linear horizontal acceleration and the ___ detects linear vertical acceleeration

utricle, saccule

the otolith organs use the ___ to detect and transmit signals, while the SCC use the ____

macula, ampulla

what is the structural set-up of the otolithic organ?

epithelial layer = macula, vestibular hair cells projecting into jelly-like otolithic membrane, calcium carbonate crystals = otoconia sprinkled on top of membrane

what is the role of the otoconia?

to assist with the displacement of the otolithic membrane

displacement of the otolithic membrane does what?

displaces the hair cells via shearing to release neurotransmitters to fire an action potential

why does the otolithic membrane need the weight of the otoconia

when there is a positional shift, the membrane will shift and stop because the otoconia hold it in the shifted position

movement of the stereocilia ____ the kinocilium leads to a(n) ___ in nerve activity; movement ___ leads to a(n) ___ in nerve activity

towards, increase, away, decrease

what is the striola

the center line of the otolithic organ membrane

what is the significance of the striola

the kinocilium of each hair cell is oriented towards it

the otolithic organs detect what 2 things?

head tilt and linear translation

a head tilt along the axis of the striola will ___ hair cells on one side and inhibit hair ceells along the other

excite, inhibit

tilting the head to one side has ___ effects on _____ hair cells of the 2 utricular maculae

opposite, corresponding

a 45 degree forward pitch to the R will do what to the semicircular canals?

excite R anterior canal and inhibit L posterior canal

a 45 degree backward pitch to the L will do what to the semicircular canals?

excite L posterior canal and inhibit R anterior canal

when you excite the R horizontal canal, you inhibit the __ _____ canal

L horizontal

what is the semicircular canal equivalent to the otolithic membrane?

hair cells suspended in the cupula, displaced by the movement of endolymph

how are the kinocilium oriented in the cupula? what does that do?

towards the medial side so that if you turn to that side you will activate the CN on that side (ie turn R, activate R vestibular nerve)

the cupula deflects ___ the direction of head movement

away from

why do the SCCs not respond to linear movements?

in linear movement equal pressure is exerted on both sides of the cupula, preventing displacement of hair cells

if the head turns to the L, what happens to the stereocilia in the L horizontal canal and vestibular nerve?

cupula displaces to the R, resulting in excitation of the L horizontal canal

if the head turns to the L, what happens to the stereocilia in the R horizontal canal and vestibular nerve?

cupula displaces to the R, resulting in inhibition of the R horizontal canal

why does the vestibular system have a high baseline firing rate

helps us detect multi-planar motion because we can detect “negative”/inhibited firing

as we age, we lose ___ which can decrease ___

stereocilia, baseline firing rate

what can happen if the loss of stereocilia is uneven between the 2 ears?

the baseline firing rate is uneven, so brain thinks it is spinning

why do we stop feeling the sensation of movement once a car gets moving?

thee weight of the otoconia prevents “jiggle” of the membrane, preventing excess firing of the vestibular nerve

once we stop accelerating, the ___ evens out the otolithic membrane

otoconia

how can the utricle and saccule tell the difference between head tilt and linear acceleration?

there is a tonic response during head tilt and a transient response during linear translation

the ____ come back to its baseline after acceleration has leveled out

SCCs

for every 1 degree of head movement, there is:

an equal and opposite movement at the eye

why is the vestibulo-ocular reflex important?

to maintain a stable gaze while moving

if you reflexively activate an eye muscle (as in the VOR), you have to:

inhibit the antagonist

in the VOR, if you turn your head to the L, you excite __ __ and inhibit __ __

R lateral rectus, L medial rectus; R medial rectus, L lateral rectus

when you turn L in the VOR, what happens to the vestibular nerve?

R vestibular nerve will decrease firing rate due to the displacement of the cupula away from its kinocilium

explain the neuroanatomy pathway behind the VOR (start at a ganglion)

vestibular input from Scarpa’s ganglion to the medial vestibular nucleus to the abducens nucleus to the oculomotor nucleus

1) turning your head to the R ____ the firing rate of the R vestibular nerve

increases

2) the R vestibular ganglion sends information to the R ________

medial vestibular nucleus

3) the medial vestibular nucleus sends excitatory fibers to the __ abducens nucleus

left

4) the abducens nucleus sends a motor output to excite the contralateral _____ muscle and uses an interneuron to excite back across the midline and ascend in the ___ to the oculomotor nucleus

lateral rectus, medial longitudinal fasciculus

5) the oculomotor nucleus activates neurons that cause the ___ muscle of the __ eye to contract

medial rectus, right

what are the 2 descending projections from the vestibular nuclei

vestibulocervical reflex (VCR) and vestibulospinal reflex (VSR)

what does the VCR pathway do?

modulates head position with respect to the SSCs

what does the VSR pathway do?

promotes upright posture by exciting spinal extensors and inhibiting flexors

the VSR is modulated by the:

reticulospinal tract, medial and lateral vestibulospinal tracts

the VSR receives input from:

otolith organs

what is the role of the VCR

responding to quick changes in head position to ensure that it stays upright

what pathway can override the VOR?

VSR

what brain region is critical for proper vesetibular processing?

cerebellum

from where does the cerebellum provide descending information to the vestibular system?

inferior vermis and flocculonodular lobe

what is the primary purpose of the vestibular-cerebellar circuits?

integrate and modulate adaptation of the VOR, integrate signals from vestibular organs to distinguish head tilts from translational movement

what is an additional purpose of the vestibular-cerebellar circuits

help distinguish what movement was self-generated and what was externally-generated

the visual and vestibular system are helpful in distinguishing: (helpful in baseball, for example)

when you are moving closer to something versus when something is moving closer to you

which cortical lobe is the target for interpreting and making meaning of sensory input such as that from the vestibular system?

parietal

what 3 sections of the parietal lobe are targets for vestibular input

parietoinsular vestibular cortex, visual posterior Sylvian area, somatosensory cortex

after traveling to the ___ of the thalamus, the vestibular information travels to ___ ___ ___ important to perception of ___ ___ and _____

VPN, diffuse cortical areas, spatial orientation, self-motion