Ears 2 Flashcards
inner ear parts
Oval Window –
Cochlea –
Auditory-Vestibular Nerve –
Vestibular Labyrinth –
oval window
vibrates, sends sound waves through cochlea
cochlea
“snail”! Pea-sized organ in which sound is transduced
organ for transduction of sound wave signals into neural signals
auditory-vestibular nerve
brings sound info to brain
vestibular labyrinth
vestibular organ of interconnected chambers
auditory pathway stages
Sound waves enter auditory canal
Tympanic membrane vibrates
Ossicles vibrate - malleus, incus, stapes
Oval window vibrates
Cochlear fluid - sends wave down basilar membrane
Sensory neuron response to the brain
basilar membrane
Membrane running down the middle of the cochlea
Thinner and stiffer at base (near oval window)
Wider and floppier at apex (like a swim flipper)
Covered with hair cells
how does basilar membrane work
Stapes contacts oval window, moves in and out like piston as sound transmitted
Fluid pumped in waves through spiral of cochlea
Fluid movement bends basilar membrane near base
Wave moves towards apex (far end)
Hairs on cells lining membrane move back and forth with flow
basilar membrane more
Pressure at oval window, pushes fluid in cochlea, round window membrane bulges out
Basilar membrane vibrates as a wave, with one position moving at its maximum
high v low frequencies basilar membrane
High frequencies die out early close to base
Low frequencies travel farther along basilar membrane
tonotopic organization
spatial arrangement where different frequencies vibrate specific parts of the basilar membrane
Presbycusis -
loss of flexibility of basilar membrane in older people, generates a loss of hearing at higher frequencies
organ of corti
A long basilar membrane, The Organ of Corti hold hair cells
As basilar membrane moves up and down, the Tectorial membrane moves up and down which pushes on hair cells.
Bending Hair cells triggers a neural signal in spiral ganglion cells (bipolar cells).
damage where can cause nerve deafness
organ of corti
inner hair cells
main transmitters of sound
spiral ganglions receive 95% of innervations from these cells even though they are outnumbered 3:1 by outer hair cells
outer hair cells
may amplify low intensity sound vibrations by rapidly changing their cell length
why is sound transduction cause mostly by inner hair cells
3X more Outer hair cells than Inner hair cells, but most transduction of sound by Inner hair cells.
One spiral ganglion cell synapses with many outer hair cells.
Many (10) spiral ganglion cells will synapse with one inner hair cell, therefore most sound detection caused by inner hair cells.
Flapping OF WHAT helps move hairs
tectorial membrane
sound transduction
As the basilar membrane moves up, the tectorial membrane pushes the stereocilia of hair cells one direction.
As the basilar membrane moves down, the tectorial membrane pushes the stereocilia of hair cells the other direction.
sound transduction cont
Tip links (elastic filament) attach stereocilia, provide a mechanical spring to open and close TRPA1 channels. When stereocilia straight, TRPA1 channels partially open, some K+ flows in. As basilar membrane moves up and down, the tectorial membrane pushes stereocilia to bend left and right. In one direction, channels are pulled open (depolarization), in other direction, channels pulled shut (hyperpolarization)
place theory
Place on the basilar membrane that vibrates the most sends signal to a certain position in the auditory cortex (tonotopic map) – each area correlated with specific pitch
frequency theory
For lower frequencies, neurons fire at the frequency of the wave (for example, a 20Hz sound might make neuron fire 20 times per second)
low v intermediate v high frequencies
Low Frequencies: (Below 200 Hz)
Only Phase Locking (No characteristic frequencies below 200 Hz)
Intermediate Frequencies: (200 Hz-4,000 Hz)
Both Tonotopic Mapping and Phase Locking
High Frequencies: (Above 4,000 Hz)
Only Tonotopic Mapping (Too fast to fire in phase)
Sound Intensity or Loudness is encoded by:
Number of neurons firing – Louder more neurons fire.
Firing rate of neurons – Louder faster firing rate.
Louder sounds cause the basilar membrane to be
displaced over a greater area causing the activation of more hair cells and to be displaced with a greater amplitude which causes greater depolarizations and hyperpolarizations leading to a greater firing rate of spiral ganglion cells.
one auditory pathway
Spiral ganglion (one side)-synapse from hair cells forms Auditory-Vestibular Nerve
Ventral cochlear nucleus of medulla (one side)
Superior olive of medulla (both sides)
Inferior colliculus of midbrain (both sides)
MGN of thalamus (both sides)
Auditory cortex (both sides)
