PHYL2002 Study Guide - Final Guide: Ampulla, Vestibular System, Otolith
Cellular Basis of Hearing and Balance
• Function of auditory system
o Peripheral mechano-transducer (cochlea) converts acoustic
energy into nerve impulses
o Encodes environmental sounds → including speech and music
o Represents sound frequency (pitch), loudness and sound source
location
• Transduction mechanism – hair cells
o Cochlear hair cells → 1 row of inner hair cells, 3 rows of outer hair
cells
o Inner hair cells → sensory receptors
o Outer hair cells → modulate basilar membrane motions
o Hair cells contain stereocilia with a taller kinocilium
o Tip links connect tips of adjacent stereocilia → provide means for
converting hair cell movement into receptor potential
o Displacement of hair bundle stretches tip links → opens cation
selective channels and depolarizes hair cell
o As linked stereocilia move, tension on tip link varies → modulates
ionic flow → graded receptor potential
o Transduction → fast and sensitive
• Ionic basis of mechanotransduction in hair cells
o Hair cell has a resting potential between -46 and -60mV
o Potential relative to fluid that bathes basal end of cell
o At resting potential → small fraction of transduction channels
open
o Displacement of hair cells causes more transduction channels to
open → causes depolarization as K+ enters the cell
o Depolarization opens Ca2+ channels on hair cell membrane →
causes transmitter release onto auditory nerve endings
o Receptor potential is biphasic
▪ Movement towards tallest stereocilia depolarizes
▪ Movement away from tallest sterocilia hyperpolarizes
o High speed demands of mechanoelectrical transduction cause
specialization of ion flux in inner ear
o K+ both depolarizes and repolarizes cell → K+ gradient largely
maintained by passive ion movement
• Organ of Corti
o Complex mechanoreceptor
o Each afferent neuron is sharply tuned to a particular sound
frequency
o Different sound frequencies vibrate at different locations along the
cochlea
o High and low pitched sounds are processed along the coiled
cochlea
o Outer hair cells normally act to amplify basilar membrane motion
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