auditory processing Flashcards
Describe the structure of the inner ear
bony structure of cochlea and semicircular canals of vestibular system
what is the cochlear
its a bony tube containing fluid in chambers separated by a thin membrane called the basilar membrane
what happens when sound pressure waves enter the ear?
the ear sets up vibrations of the tympanic membrane (ear drum)
these virbations are then transmitted to the sensory receptors in the cochlea
what happens when ‘sound’ enters the ear
the stapes vibrates and applies pressure to the fluid in teh upper chamber (scala vestibuli)
the fluid moves to the apex of the cochlea (helicotrema)
the fluid pressure is relieved by movement of additional membrane at the round window, which bulges out
what leads to the vibration of the basilar membrane
compression and rarefaction of air in the outer ear
as fluid moves around the helicotrema….
it exerts force onto the basilar membrane
what is the structure of the basilar membrane like at the apex
5 times broader, thicker and floppier
descripe the tonotopic organisation of the basilar membrane
high grequencies vibrate at round window end, low frequencies at apex
what is the organ of corti comprised of
two rows of hair cells (inner and outer)
what is the function of inner hair cells
main receptors responsible for perception of sound
describe the structure of where hair cells are embedded
tips are embedded into gelatinous membrane (tectorial) that protrudes into a special fluid chamber called the scala media which has very high K+
what happens to tips of hair cells when basilar membrane vibrates
shearing motion, deflected back and forth as tips adhere to tectorial membrane
what about the hair cells can enhance the tonotopic map
fact that they are also longer and floppier at the distant end of the cochlea
what ahppens to voltage when hair cells are pushed
the voltage change across the cell membrane is proportional to teh force encoding amplitutide and phase in their graded receptor potential
what are tip links and what do they do
fine structures that connect the tips of stereocilia together
gate cation cahnnels
when pushed open, = K+ influx
will the stimulus strength required to produce a 1mV response in hair cells be the same across the length of the basilar membrane
no because of tuning/sensitivity to different frequencies
what is the relationship between the magnitude of sound and the perceived loudness
logarithmic = 10x the sound pressure for each increment in perception
what explains our ability to perceive large dynamic range of volume
additional amplifiers = outer hair cells which generate sound in the ear to sharpen frequency tuning of inner ahair cells
what is the speed of mechanical gating of ion channels
fast duh
what do recordings from hair cells show
that they respond to sounds with graded responses which means the refractory period of spikes would be very limiting
where is the ntsm released onto
the spiral ganglion neurons and then transmitted with action potentials
why could a rate code not be used by receptors
it would lose resolution of timing (phase)
hair cells fire ….. but auditory interneurons ap fire ….. at high frequencies
fast
slower
is ap firing better or worse at lower amplitudes when its quieter
worse lol
what lines up with the timing of spike generation
precisely in phase with depolarisation of hair cells
why do we need multiple afferent interneurons per hair cell
because they miss info individually bc of the refractory period. so graded signal is converted to spike code for transmission to higher centres for processing
how do we improve dynamic range
having different neurons with different thresholds for spike generation
where do the spiral ganglion neuron cells project to
the cochlear nuclei in the brain stem in medulla
describe the projection to the auditory cortex
its ascending pathway via relay nuclei in the mid brain = inferior colliculus (IC) and medial geniculate nucleus (MGN)
what type of neurons does the IC contain
ones that respond only to specific sound locations
what is cortex projection involved with
complex pattern recognition (speech)
what can brain stem nuclei do
they are projected onto by spiral ganglion neurons. they compare sounds coming from two ears to determine the location of sounds in space (because of delay in sound reaching the more distant ea)
