Hearing cont'd, Balance Flashcards
stereocilia
microvilli bundles located on top of hair cells
tip link
- specialized mechanoreceptors
connects tip of each stereocilium in a hair bundle to the side of the next larger stereocilium
do stereocilia get progressively taller or shorter as we go along a hair cell?
taller
steps to depolarization of hair cell in the ear
- at rest, gated spring is relaxed
- stereocilia bend toward taller stereocilia, this causes gating spring to stretch
- K+ channel opens and K+ from endolymph enters the cell, causes depolarization
Hearing physiology steps
1) sound waves enter auditory canal, strike tympanic membrane, it vibrates
2) vibration transferred to middle ear (malleus>incus>stapes)
3) foot plate of stapes vibrates in oval window, causes perilymph in scala vestibuli to vibrate
4) vestibular membrane to vibrate and transfer to endolymph
5) displacement of basilar membrane, movement detected by hair cells
6) vibrations is scala vestibuli (perilymph) and basilar membrane are transferred to scala tympani out through the round window
how are high and low pitch received?
low - stimulates cells to lose helicotrema of basilar membrane
high - stimulates cells close to oval window of basilar membrane
neural pathway of hearing
cochlear nerve > cochlear nuclei > superior olivary nucleus OR
cochlear nuclei > inferior colliculus (midbrain) > medial geniculate (thalamus) nucleus > primary auditory cortex (temporal lobe)
static equilibrium
structures involved?
our heads position relative to the ground
structures: macula of utricle and saccule
macula
contains specialized hair cells
otoliths
creates mass for otolithic membrane
have crystal-like structure
otolithic membrane
gelatinous-like mass that moves w gravity
stereocilia in static equilibrium
microvilli that have 1 tall hair cell called a kinocilium
- have tiplinks attaching each of the stereocilia
- endolymph is in here, when tiplinks open, K+ channels enter and cause depolarization
how does the rest of static equilibrium work?
- hair cells are stimulated by otoliths
- the otoliths move in response to gravity and patterns of action potentials change
- involved in Subconscious perception: allows for subtle adjustments to muscles of back and neck, restores head to neutral position
dynamic equilibrium
structures involved?
- signals about whether our head is accelerating or decelerating and which direction it might be moving in
structures: ampullae of semicircular canals (they contain endolymph
cristae
specialized endothelial region in ampulla
includes hair bundle, hair cell and supporting cell
cupula
- hair bundles located here where they detect movement
- acts as a float in fluid, as it movies, it will tilt hair bundles and open tip links which open K+ gated channels, causing depolarization
- depending on which of the 3 cupulas move and in which direction, (which of the 3 ampullae) it determines the perception of which plane we are moving in
more about the physiology of dynamic equilibrium
- as head moves more, cupula moves in opposite direction head movement (inertia)
- stimulation stops when fluid in canals catches up to cupula
- when movement of the head stops, endolymph continues to move in the same direction and so the cupula will also continue to move
neural pathways for balance
this is a mess but:
vertibular nerve > vestibular nuclei > to one of 3 places:
- cerebellum (subtle adjustment, posture)
- motor nuclei (control eye muscles to see where we’re going)
- thalamus on to the vestibular area of the cortex (postcentral gyrus)
explain what happens in the spiral organ
all hair cells synapse w cochlear nerve
hair cells are stuck in tectorial membrane but are more stuck to basilar membrane
so when basilar membrane moves it bends the hair cells to open mechanically gated ion channels
inner hair cell
gets sound info for hearing
outer hair cells
3 of them
take waves and use for proprioceptive info
ex. adjusting tension in tympanic membrane
scala tympani and scala vestibuli
contain perilymph
- sound waves enter scala vestibuli (superior) and travel through cochlea until it reaches the end called the helicotrema
- helicotrema connects scala tympani and wave travels back through to round window
cochlear duct
contains endolymph
also inside is: tectorial membrane, spiral organ and basilar membrane
cochlea
3 tubes that have been swirled into what looks like a snail shell
semicircular canals
anterior, posterior and lateral: one for each plane of movement
endolymph
high K+, low Na+
found in membranous labyrinth
perilymph
high Na+, low K+ (like in an axon)
found in bony labyrinth
pitch
wave frequency
volume
wave amplitude
sound
the interpretation of vibration
made of pockets of compressed air and pockets of not compressed air
structures involves w dynamic equilibrium
ampullae of semicircular canals
structures involved w static equilibrium
utricle and saccule
inner ear
fluid filled, where air waves are turned into fluid
- semicircular canals
- cochlea
+ more
round window
where sound waves exit inner ear
oval window
membrane w fluid on one side and air on the other
- when hit by foot of stapes, fluid on other side vibrates
auditory tube
- equalizes pressure in ear from medial side of tympanic membrane
- allows air from throat to come up to inner ear
- when ears pop it’s actually the sounds of auditory canals opening
auditory ossicles
small bones in middle ear
malleus - makes contact w tympanic membrane
incus - synovial joint i think w malleus
stapes - foot plate hits oval window
tympanic membrane
eardrum
very delicate
- vibrates when compressed sound waves hit
- as it vibrates, the malleus vibrates, moves incus, which causes foot plate of the stapes to hit the oval window
middle ear
air filled cavity
- tympanic membrane
- auditory ossicles: malleus, incus, stapes
- oval window
- round window
- auditory tube
cerumen
earwax, produced by glands in external auditory canal
filters debris
auricle/pinna
outer structure of the ear
collects soundswaves
external ear
air filled cavity
- auricle
- external auditory canal
- temporal bone
