Lecture 39: Physiology of Auditory and Vestibular Systems Flashcards
Where do high and low frequencies cause the most deflection along the basilar membrane?
High: greater deflection where it is narrow and stiff
- near oval and round windows
Low: greater deflection where it is loose and flexible
- near helicotrema
*frequency of sound coded by where there is the greatest deflection
Depolarization of the Hair Cell (4 steps)
- tip-links on apex of stereocilia cause TRPA1 cation channels to open due to movement of endolymph
- potassium enters hair cell, causing depolarization, which opens voltage-gated Calcium channels at base of cell
- Calcium influx causes Neurotrans vesicles to fuse w/basilar membrane and release GLUTAMATE into synaptic cleft
- stimulates afferent cochlear nerve fibers that transmit signal to CNS
What is the difference between an upward and downward placement of the basilar membane?
Upward: creates shearing force that results in lateral displacement of stereocilia (depolarization)
Downward: creates shearing force that results in hyperpolarization of stereocilia
Stria Vascularis
- produces endolymph w/high levels of K that fills entire membranous labyrinth
- maintains endocochlear potential (+80 mV)
- forms blood-labyrinth barrier (BLB) –> one of main sites of drug entry to access the inner hair cell
Inner Hair Cells
- primary source of auditory information (single layer)
- synapse w/peripheral terminal of primary afferent sensory neuron
- efferent neuron modulates activity
Outer Hair Cells
- amplify sound waves resulting in basilar membrane movement (three rows)
- contractile –> property boosts the mechanical vibrations of the basilar membrane (amplifying affect)
- synapse w/afferent peripheral terminal and terminals from efferent neurons
Otoacoustic Emissions (OAE) and testing (what does it screen for?)
- retrograde movement of basilar membrane causes ear to make sound that displaces the tympanic membrane
- measured in external auditory meatus
- testing measures presence/absence of sound waves generated by outer hair cells
- screens for sensorineural hearing loss but cannot detect auditory neuropathy
Olivocochlear Efferents (function)
- reduce electromotility of outer hair cells (dec. basilar movement)
- reduce response of inner hair cells and auditory nerve fibers
Medial Ear Afferents (function)
- attenuate sound (bilateral response to high sound lvls)
- contractions dec. sound transmission
- prevent damage, low frequency masking, protect hair cells from damage to intense sounds
- implicated in TINNITUS
Autonomic Efferents (function)
- from CN VIII
- regulate vascular tone in blood supply to cochlea (sympathetic adrenergic fibers)
Functions of Dorsal and Ventral Cochlear Nuclei
Dorsal: integrate acoustic info w/somatosensory info
Ventral: processing temporal and spectral features of the sound
Functions of Medial and Lateral Superior Olivary Complex
- receives EXCITATORY input
- MSO: TIME differences to help localize sound (map)
- LSO: INTENSITY differences to help localize the source of sound (map)
Function of Inferior Colliculus
- suppresses info related to echoes
- info about time/intensity converge to help create precise origin of sound location along the horizon
Function of Medial Geniculate Nucleus
- processing features of speech inflections
- precise info regarding intensity/frequency/binaural properties of sound are integrated and relayed onward
Function of Primary and Secondary Auditory Cortex
PAC: conscious perception of sound, higher order processing of sound
SAC: multiple areas; less specifically organized; responds to more complex sound (music), identifying a sound (naming), and speech
