auditory function and balance Flashcards
sound transduction: explain the mechanisms of sound transduction from the middle ear to the cochlea
how many ossicles (small bones) are present in the middle ear
3
what do the middle ear ossicles do
transmit vibration of tympanic membrane onto cochlea of innner ear, matching impedance and reducing loss in energy as vibration goes from air to cochlea (some reflected, some transmitted; similar to violin bridge)
what is the shape of the cochlea, and what is it filled with
snail-shaped organ filled with liquid
define impedance
measures reluctance of system in receiving energy from a source
define resonant frequency
frequency at which the impedance of the system is minimal; changes locally
what controls tension of tympanic membrane
malleus and incus, which can be adjusted by tensor tympanic muscle and stapedius muscles
in the cochlea, what does the motion of the stapes generate
difference in pressure between the two liquid-filled chambers
what does the difference in pressure created by the stapes in the cochlea cause
basilar membrane to vibrate (part of Organ of Corti)
what are the 4 sections of the Organ of Corti in the cochlea, and diagram
basilar membrane, tectorial membrane, hair cells, supporting cells
function of basilar membrane, and how it does this
frequency analyser, by breaking complex sounds down by distributing energy of each component frequency along its length using active and passive (impedence) processes
structure of basilar membrane and how related to function
elastic structure that vibrates at different positions along its length in response to different frequencies; impedance, and therefore local resonant frequency, of basilar membrane varies along its length
what is present along the whole length of the basilar membrane to detect all frequencies
hair cells, which act as sensory receptors
structure of hair cells
have a hair bundle on projecting surface, which is a cluster of modified microvilli (stereocilia)
name of how hair cells produce electric signals
mechano-transduction
process of mechano-transduction
motion of basilar membrane deflects stereocilia away from modiolus -> when they bend towards tallest stereocilium, K+ channels open -> K+ enters from endolymph -> changes cell internal voltage, causing hair cell to depolarise -> opens Ca2+ channels in body of hair cell -> glutamate released from base depolarises axon, creating action potential that travels towards brain
how are stereocilia connected to hair cells
filamentous linkages called tip links
function of tip links on stereocilia
work as small springs stretched by stereocilia’s sliding
what are response currents in mechano-transduction a result of, concerning tip links
opening of ion channels activated by stretching of tip links (as tip links share location with ion channels)
effect of external stimulus on mechano-transduction ion channels, tip links and whole of stereocilia
mechano-transduction ion channels open, relaxing the tip links and the whole stereocilia
what happens to measured stiffness when mechano-transduction ion channels open and why
becomes negative, as healthy stereocilia actively complies with direction of stimulus (not passive -> actively swings when triggered)
4 aspects of active process by which cochlea has sensitivity and sharp frequency selectivity
amplification, frequency tuning, compressive non-linearity, spontaneous otoacoustic emission
evidence for amplification
particular segment of a living basilar membrane vibrates far more in response to its resonant frequency than a dead basilar membrane
evidence for frequency tuning
a dead basilar membrane produces a broad response and it is not tuned for a specific frequency; a living basilar membrane instead selectively amplifies single frequencies
evidence for compressive non-linearity
basilar membrane motion is augmented 100-fold during low-intensity stimulation, but amplification diminishes progressively with the increasing intensity of the stimulus (compress dynamic range of sound to limit of basilar membrane vibration)
