auditory systems Flashcards
properties of sound
frequency:
number of compressed or rarefied patches of air that pass out of ear per second (Hz)
amplitude:
air pressure difference between peaks and troughs (dB) - logarithmic scale
human ranges of hearing
20-20,000Hz
140db = threshold of pain
120dB = threshold of high risk (prob much lower than this
structures in outer, middle, and inner ear
outer = pinna, ear canal, tympanic membrane
middle = oval window, ossicles
inner = vestibule, cochlea
outer ear structures functions: pinna, tympanic membrane
pinna:
outer part of ear
determine whether sound is coming from above or below - vertical differences
tympanic membrane:
ear drum
moves in and out as sound waves hit it
end of outer ear and beginning of middle ear
3 ossicles of middle ear
3 bones: malleus, incus, stapes
tympanic membrane -> malleus -> incus -> stapes -> oval window
malleus -> incus = rigid connection
incus -> stapes = flexible connection
middle ear mechanism with sound waves
compression phase:
tympanic membrane is pushed inwards
stapes pushes into oval window
round window (below oval) bulges outward to relieve pressure
rarefaction phase:
tympanic membrane pulled outwards
stapes is pulled back so oval window pulls outwards
round window is pushed in to relieve pressure
middle ear - oval and round window
oval window leads to scala vestibuli
round window leads to scala tympani
scala vestibuli and scala tympani are part of the cochlea - fluid filled
scala vestibuli = goes up cochlea
scala tympani = comes back down cochlea
concentration of sound into cochlea
cochlea is fluid filled - higher impedance than air
therefore need to concentrate force to a smaller area or it would be too quiet to hear
therefore middle ear ossicles amplify sound to exert ~20x more pressure on oval window than the tympanic membrane
cochlea anatomy - scala vestibuli, tympani, media
scala vestibuli and tympani contain perilymph (0mV - no PD)
scala media contains endolymph - high K+ conc - generates endocochlear potential +80mV
when oval window is pushed in, fluid moves up from base of scala vestibuli to top of the coil - helicotrema
helicotrema connects to scala tympani where fluid moves down to the round window
cochlea anatomy - organ of corti
connects from scala media (tectorial membrane) to basilar membrane
moves depending on movement of basilar and tectorial membranes
cochlea anatomy - basilar membrane
runs through whole length of cochlea
base (round window) is narrower - moved by highest frequency sounds (high pitch)
apex is wider - further into coil of cochlea = lower frequency sounds
creates a tonotopic map –> different frequencies cause maximal displacement of basilar membrane in different regions
cochlea anatomy - impact of basilar membrane on hair cells
movement of stapes on oval window causes up/down movement of basilar membrane which is connected to hair cells and mechanically moves them
(tectorial membrane also moves)
cochlea anatomy - hair bundles structure
stereocilia = single structure, made of action - strong so move from base, don’t waft like hair
outer hair cells (OHC) and inner hair cells (IHC)
IHCs are primary sensory receptors of auditory system
hair bundles connected by tip links
IHC moved by movement of membranes and fluid
cochlea anatomy - IHCs function with sound waves
as tip links are pulled, mechanically gated ion channels are pulled open
non-selective cation channel
huge depolarisation due to difference between extracellular endolymph (+80mV, high K+) and perilymph (0mV, low K+)
depolarisation = Ca2+ channels open = Ca2+ enters = glutamate released into synapse = continuation of action potential through afferent neuron
graded receptor potential - more movement of membrane = more channels open = greater potential
very quick changes between depolarised and not as sound wave travels through
cochlea anatomy - OHCs function
electro-motile - move with electrical signal
cochlear amplifiers - without them, sound would be too quiet
