Physiology of Auditory and Vestibular Systems Flashcards
describe hair cells?
auditory receptors with stereocilia located between basilar membrane and reticular lamina - responsible for stimulus responsive cation entry
cell body releases glutamate onto efferent nerve endings (does not create an AP itself, but glutamate causes an AP in the nerve)
afferent nerves regulate the response
specialised structure at the tip which gates or closes the TMC1 channel mouth depending on the tilt of cilia
how is AP frequency modulated?
tonic release of glutamate
common feature in all 3 sensory organs in the labyrinth?
hair cells
cochlea, semi-circular canals, otolith organs/otocysts
what is sound?
repetitive changes in density of air
an object vibrates > produces changes in air pressure > air vibrates and travels in 3 dimensions > we hear a sound
(speech = vocal cord vibrations)
give a brief overview of how hearing occurs?
sound > vibration of air > vibrate the tympanic membrane the malleus then incus then stapes > vibration spreads to cochlea > vibration of air converted to movement/vibration of fluids in cochlea > vibration in cochlea is captured by hair cells > transduction (physical vibration is transduced to neural energy) > perceived in auditory cortex
what are the 3 mechanisms for impedance matching?
- area ratio of the eardrum to the stapes footplate (vibration converges onto smaller area)
- lever action of the ossicles
- buckling of the eardrum (increases pressure)
where are hair cells found in the cochlea?
sit on basilar membrane in the organ of corti within the scala media of the cochlea
describe transduction through the cochlea?
organ of corti hair cells > basillar membrane > tectorial membrane
what separates the 3 layers of the cochlea?
reissner’s membrane separates scala vestibuli and tympani
basilar membrane separates scala media and tympani
anatomy of cochlea?
less rigid at apex, so requires less force to get movement of basilar membrane and therefore fluid and therefore hair cells (low frequency sounds)
more rigid at base so needs lot of force to move basilar membrane (high frequency?)
scala media closed off at apex
scala tympani and vestibuli connect at helicotrema (at apex)
scala tympani meets oval window
scala vestibuli meets round window
pressure at oval results in complimentary motion at round
endolymph movement in cochlea causes what?
movement of stereocilia > displacement of organ of corti > change in tilt of stereocilia > change in entry level (increased/decreased?) > release of glutamate onto neurons
describe hair cells?
basis for tontopy - hair cells are basically tuned to different frequencies (different frequency sounds stimulate hair cells at different locations)
describe current in hair cells?
K+ current is inwards rather then outwards
fluids in inner ear are therefore different to other cells
- endolymph has high K+ conc, low sodium (opposite to perilymph in Scala vest/tmp) creating inwards conc gradient
hair cell is slightly depolarized at rest (due to potassium gradient?)
potassium enters the hair cell and is recycled via channels, transporters and gap junctions
inner hair cells?
main source of afferent signal in CN VIII, main part of sound perception
multiple hair cells innervated by a single afferent
outer hair cells?
primarily get efferent inputs
control stiffness and amplify membrane vibration
how do outer hair cells act as cochlear amplifiers?
contains motor protein “prestin” in membrane which can change the length of the cell (changes ratio of B membrane and T membrane)
respond to sound with both a receptor potential and a change in length
length change of OHC > increased movement of BM > increased bending of IHC > increased transduction
what are the 2 mechanisms for frequency coding in CN VIII?
place code
temporal code
how is the auditory system different to the visual system>
signals from right/left are all mingled
as you need to localise where sound is coming from
how is tonotopy preserved in the auditory system?
VIII nerve branches into 3 cochlear nuclei
- dorsal cochlear nucleus (DCN)
- posteroventral cochlear nucleus (PVCN)
- anteroventral cochlear nucleus (AVCN)
tonotopy ensures that each neuron innervates several different areas and different neuron types
how and where does sound location mainly occur in the pathway?
determined by time taken (interaural time difference) and intensity of sound at arrival at the ears
lateral and medial superior olives involved
- medial = computes sound arrival at the two ears (e.g ipsilateral ear earlier than the contralateral, this generates an “interaural time difference” using a “delay line”
functions of vestibular system?
provide information on gravity, rotation and acceleration
reference for somatosensory and visual systems
integration of arousal, conscious awareness of body via connections with vestibular cortex, thalamus and reticular formation
allows for gaze and postural stability, orientation and detection of linear and angular acceleration
what does the vestibular organ sense?
head angular acceleration (semi-circular canals) - head rotation
head linear acceleration (saccule and utricle) - translational motion, gravity and extension by head tilt
peripheral sensory apparatus of vestibular system?
detects and relays information to vestibular nucleus about head angular and linear velocity to central processing system
central processing system of vestibular system?
processes information in conjunction with other sensory inputs for position and movement of head in space
