BMS11004 WEEK 8 - THURSDAY Flashcards
middle ear, cochlea, basilar membrane, hair cell
outline what sound actually is
particles move backward/forward in small area ‘vibrating’
sound waves travels along the whole length, as move create rareified and compressed air
outline rareified air
low density of particles
outline compressed air
high density of particles
outline sound frequency
number of compressed or rareified patches of air that pass by our ears each second, expressed in Hz
describe what frequency like at less or more particles
less particles = low frequency sound
more particles = high frequency sound
define intensity/amplitude of sound
air pressure difference between peaks and troughs, in dB
what does greater intensity/amplitude mean
bigger air pressure difference
what is human hearing range
20-20,000Hz
what is baseline of profound hearing loss
100Db
why does 0Db not mean there’s no sound
logarithmic scale
what is role of the outer ear
funnel sound wave
more sensitive to sound from infront than from behind
convolutions of pinna (outer ear squiggle) for sound localisations
briefly outline structure of middle ear
tympanic membrame, 3 ossicles, oval window, cochlea
what is tympanic membrane (middle ear)
ear drum, move back/forth like speaker
when moves, causes movement in ossicle
name 3 ossicles of middle ear
malleus, incus, stapes
what is oval window (middle ear)
covers base of cochlea, similar to tympanic membrane but smaller
why would oval (middle ear) hardly move if moved directly by sound
air-fluid interface, fluid has greater inertia
cochlea is fluid filled compartment
explain how middle ear transfers sound
rareified patches of air pulls tympanic membrane outwards so pulls oval window out of cochlea (pull fluid in cochlea in opposite direction)
transfers movement of tympanic membrane from oval window to create fluid movement in cochlea
middle window concentrate force of sound waves against larger tympanic membrane onto smaller oval window
how does ossicles of middle ear amplify sound
exerts 20x more pressure onto oval window than to tympanic membrane
overcome greater impedance of cochlear fluid
what 3 fluid-filled compartments surround the cochlea spiral
scala vestibuli, scala media, scala tympani
outline scala vestibuli (cochlea)
connected to top of oval window, gets pushed at bottom if oval window gets moved in, pushes fluid (perilymph) down into scala tympani
outline scala tympani (cochlea)
filled with perilymph, connect at large end to round window
outline scala media (cochlea)
filled with different solution, endolymph, with very high extracellular K+ surrounds stereocilia (hair bundles)
what is organ of corti
mid of cochlea
top of organ of corti has tectorial membrane (underneath there are outer hair cells)
what is role of hair cells in organ of corti (cochlea)
inner line = primary transducers of auditory system
outer line = less important, help amplify cochlea response, help inner hair cell listen to low db
explain hair bundles and tip link
hair cell has hair bundle at apex, made of stereocilia which is connected by tip links (broken by loud music)
when tip links pulls, open mechanoelectrical transducer channels (non selective cation channel) and allow flow in of cation, depolarise hair cell
outline basilar membrane
runs along cochlea, moved when cochleal fluid moves
thick at base and thinner at apical end
what does different frequency sounds cause in basilar membrane
maximal displacement
high frequency cause more movements
low frequency makes apical end move more
tonotopic map (cell responsive to different frequencies found in different place on each levels)
explain how movement of the basilar membrane not linear
amplitude of movement not proportional to the sound pressure
how does basilar membrane displacement (bowing upward) affect hair cells
stapes move outward, BM move upwards
moves hair cell up, stretch tip link, opens channel- depolarisation
how does basilar membrane displacement (bowing downward) affect hair cells
stapes move inward, BM move downwards
hair cells move down, relaxes tip link, shut channel- hyperpolarisation
why is endolmyph at a higher voltage
high K+
why is perilymph at a lower voltage
low K+
describe why outer hair cells are electromobile, and what this allows
when cell voltage change, MP change, they move and change size
so are able to amplify movement of basilar membrane, acting as cochlear amplifier
