Inner Ear Flashcards
anatomy of inner ear
vestibule and cochlea
vestibule
receptors for balance
modiolus
hollow core of cochlea
contains the auditory nerve and cell bodies of auditory neurons which forms spiral ganglion surrounded by osseous spiral lamina
osseous spiral lamina
a bony shelf
winds around the modiolus
3 scalae chambers
scala vestibuli
scala media
scala tympani
2 membranes to separate scalae
Reissner’s membrane
Basilar membrane
Reissner’s membrane
separates scala media from scala vestibuli
helicotrema
scala vestibuli and tympani connect
joint opening at the apex of the cochlea
endolymph
fluid in scala media
high K+, low Na+
perilymph
fluid in scala vestibuli and tympani
high Na+, low K+
organ of corti
sits on basilar membrane
composed of auditory receptors (hair cells), their supporting cells, and their nerve supply ends
inner hair cells (IHCs)
innervated by Type I fibers 90-95% of Type I fibers connect to IHCs have one row in organ of corti afferent innervation: many-to-one flask shape
outer hair cells (OHCs)
3-5 rows in organ of corti innervated by Type II fibers 5-10% of Type II fibers connect to OHCs cylindrical shape afferent innervation: one-to-many basal nucleus
tectorial membrane
an acellular, gelatinous membrane
fixed only on its inner edge–attached to spiral limbus
contact with the tips of the longest stereocilia of the OHCs, no contact with IHCs
moves in wind-shield-wiper motion
traveling wave of the basilar membrane
displacement of BM is caused by perilymph
wave travels from base to apex
wave grows gradually in amplitude, meets a maximum point then dies out quickly
frequency selective
base = high frequency
apex = low frequency
frequency selectivity
BM responds selectively to frequencies
tuning curve
sharply tuned
agggh IDK
characteristic frequency (CF)
best frequency
the frequency of a sound at which the BM response is highest (amp is highest)
non-linear
intensity resolution
nonlinearity at CF
linearity at non-CF
2 types of cochlear mechanincs
passive and active
passive cochlear mechanics
represented as broadly-tuned component of the traveling curve
determined by physical properties of BM
active cochlear mechanics
produce sharp tuning at CF
amplify the traveling wave as it passes through the cochlea
result from an active source of mechanical energy in the cochlea
OHCs are responsible for active mechanics –> OHC loss results in the loss of sharply-tuned components of the traveling wave and nonlinearity
response process of hair cells in cochlea
deflection of stereocilia –> opening of K+ ion channels –> depolarization of hair cells –> release of neurotransmitters
how does deflection of the stereocilia occur?
OHCs: shearing (breaking) force between stereocilia and tectoral membrane
IHCs: movements of fluids in the subtectorial space causes bending of the stereocilia
how are the K+ ion channels opened?
K+ ion channels open at the tip of the stereocilia only when the stereocilia deflects away from the modiolus
how are the hair cells depolarized?
K+ ions flow into hair cells –> hair cells depolarize
what happens when the neurotransmitter is released?
Glutamate is sent to the synaptic cleft –> activates the auditory nerve fibers
properties of responses of hair cells
frequency selectivity
intensity resolution
