Physiology Auditory and Vestibular System Flashcards
what makes up hair cells
stereocillia which vary in length
kinocillum which marks the orientation
how do hair cells create action potentials
Tips of sterocilia; potassium (TMC1) channels which are maximally open when the hair cell tilts in one direction and maximally closed when the hair cell tips in the other direction
Entry of potassium has consequences, will generate the depolarisation of hair cell allowing hair cell to release glutamate. Glutamate will act on efferent nerve endings
cell body releases glutamate onto efferent nerve endings which allows modulation of AP frequency in response to stimulus
what do the otolith organs sense
tilt and acceleration
what determines the pitch of sound
frequency
what determines the volume of sound
amplitude
what are the steps between sound being produced and us hearing it
Sound = vibration of air
= vibrate the eardrum, the malleus, the incus, and the stapes
= the vibration spreads to the cochlea.
= vibration of air is converted to movement/vibration of fluids in the cochlea
= the vibration in the cochlea is captured by hair cells
= transduction (physical vibration is transduced to neural energy)
= Perceived in the auditory cortex
how does the middle ear amplify sound
3 methods:
- area ratio of ear drum to stapes foot plate (20:1)
- lever action of ossicles
- buckling of ear drum (causes a sound pressure increase)
what does reissners membrane do
separates scala vestibuli and scala media
what does the basilar membrane do
separates scala media from scala tympani
what part of cochlea goes into round window (how sounds leaves cochlea)
scala tympani
what part of coclea recieves input from oval window
scala vestibuli
what connects the scala vestibuli and tympani
the helicotrema
what is responsible for transduction in the coclea
organ of corti hair cells
basilar membrane
tectorial membrane
is the perilymph in the scala tympani and vestibuli continuous
yes
what fluid is in the scala media
endolymph
what structure allows us to discriminate pitch and how
basilar membrane
-is felxible an vibrates in sync with fluid motion - high pitched sounds move base of membrane, low pitches move the B< at the apex of the cochlea
where hair cells located
in organ of corti, between basilar membrane and reticular lamina- their tips are in the tectorial membrane
where do hair cells synapse
on bipolar neurones with cell bodies in the spiral ganglion
what membrane must vibrate for hair cells to move
tectorial (where the hair cells have their tips)
do all hair cells respond to the same sound
no hair cells are tuned to different frequencies
what liquids in ear have highest potassium concentration- what does this mean
higher K+ conc in endolymph (tips of hair cells in endolymph, when channel open when moved potassium will enter the cell through the potassium channel and cell will depolarise)
what causes a hair cell to depolarise or hypoerpolarise
Displacement of the hair bundle toward the tallest stereocilia depolarizes the hair cell, while movements parallel to this plane toward the shortest stereocilia cause hyperpolarization.
what state is the hair cell in at rest
slightly depolarised
mutations in what channels can cause inherited forms of deafness
potassium channels, can recycle the ion
what is the different innervation of the outer and inner hair cells
outer hair cells- get efferent inputs (control stiffness, amplify membrane vibration)
inner hair cells- afferent to CN VIII via cochlear nucleus, perception of sound
what is the cochlear amplifier
outer hair cells outnumber inner hair cells
OHC respond to sound with a receptor potential AND a change in length (done by motor protein prestin)
this changes spatial relationship between basilar mem and tectorial mem
modulates responsiveness of auditory system
how does furosemide affect cochlear
inactivates membrane motor of outer hair cells
what are the auditory nerves two mechanisms for frequency coding
place code (firing rate of neurones- important in sensitivity of hearing, low level sounds) temporal code (times at which these firings occur- important in identifying onset and offset of the sounds)
what is the central pathway of the auditory system
organ of corti
spiral ganglion
axons form cochlear nerve
joins with vestibular nerve
internal acoustic meatus
enters brainstem at cerebellopontine angle
cochear nuclei (info sent to both ventral and dorsal nuclei)
from dorsal CN- most fibres cross midline and ascend in the contralateral lateral lemniscus (others in ipsilateral lateral lemniscus)
from ventral CN- some fibres ascend in the lateral lemniscus bilaterally but most decussate to the contralateral superior olivary nuclei (in trapezoid body) (some fibres synapse in ispislateral superior ON)
this then projexts upwards into lateral lemniscus
as both dorsal and ventral nuclei have some fibres that decussate and some who dont, info from both ears travels bilaterally
both sides then reach inferior colliculus
then projects to ipsilateral medial (music goes medial) geniculate body
(in thalamus)
then project to primary auditory cortex (superior temporal gyrus, under lateral fissure)
what are the two components of the auditory pathway
primary (lemniscal) pathway- main pathway through which auditory information reaches the primary auditory cortex
non lemniscal pathway- unconscious perception (attention, emotional response, auditory reflexes)
what is tonotopy
spatial arrangement where sounds of different frequency are processed in the brain
(achieved as branches of CN VIII go to three cochlear nuclei: dorsal, posteroventral, anteroventral)
what is responsible for locating the sound source in space
superior olivary nucleus- computes sound arrival at the two ears (ipsilateral earlier than contra)
what forms a full spatial sound map
inferior colliculus
what is repsonsible for indifying and pocessing complex sounds
the primary auditory cortex
how does the supeiror olive nucleus determine differences in sound between ears
each SO neuron gets a depolarizing (from ipsilateral ear) and hyperpolarizing (from contralateral ear) signal
(inhibition from other ear)
determines the net excitation forwarded to inferior colliculus
what are the roles of the vestibular system
provides information on gravity, rotation, acceleration
is a reference for the somatosensory and visual systems
allows for gaze, postural stability, sense of orientation, direction of linear and angular acceleration
what are the respective directions sensed by the utricle and saccule (otolith organs)
u= horizontal s= vertical
(head linear acceleration- translational movements in x,y,z axes)
(together sense linear acceleration and gravity)
what senses angular head rotation (around x,y,z axes)
semi circular canals
what are crista
sheets of cells in the semicircular canal where hair cells are clustered
what are ampulla
bulge along the SCC that contain crista
what do the cilia in the SCC project into
gelatinous cupula
why are all the kinocili in the SCC orientated in the same direction
so all excited or inhibited together
what are the SCC filled with
endolymph
what shares a movement plane with the posterior canal of one ear
the contralateral anterior canal
what happens to the right anterior canal when the left posterior canal is excited
is inhibited
what happens to the right horizontal canal when the left horizontal canal is inhibited
is excited
where are hair cells in the otolith organs
macula- project from here to the otolithic membrane which has otoconia (calcium carbonate crystals)
what is the stiola
divides the hair cells of the otolith organs into two populations with opposing polarities (allows otolith to have multidirectional sensitivity- on one side will depolarise exciting afferents, on other will hyperpolarise inhibiting afferents)
what in otolith organs will cause a release of glutamate
otoconia (calcium carbonate crystals on otolithic membrane) dispacement due to change in tilt of sterocilia
what is the central vestibular pathway
vestibular nerve vestibular ganglion vestibular nuclei from here: -cerebellum -vestibulospinal tract -medial longitudinal fasciculus (both ascending and descending components): -- ascending to abducent, trochlear and oculomotor nuclei
-medial lemniscus (to thalamus and cerebral cortex)
what are the three major vestibular reflexes
vestibulo- ocular reflex (keeping eyes still when head moves)
vestibulo-colic reflex (head still in space/ on level plane when walking)
vestibular spinal reflex (adjust posture for rapid changes in position)
why does alcohol affect the VOR
alcohol enters the blood, and then into the cupula. The cupula becomes less dense. It floats in the endolymph more
