Cochlea and auditory system Flashcards
what type of receptors?
mechanoreceptors
What is sound?
What does SPL mean?
a compression wave = moves back and forwards
SPL = sound pressure level
What does frequency mean?
What does amplitude mean?
how often
sound intensity
Route of sound?
ear canal to ear drum = well adapted to transmitting frequency
why have 2 ears?
localising sounds
What is found in the outer ear?
auricle, external auditory canal, ear drum
What is found in the middle ear?
temporal lobe of brain, temporal base, hemmar, anvil, stirrup
What is found in the inner ear?
semicircular canals, oval window, cochlea, round window, nerves, eustachian tube
Tympanic membrane?
eardrum
includes: malleus, stapes and incus (all behind)
(at footplate of the stapes is the oval window)
Simple resonance model? near apex = high or low freq? near base = high or low freq? basiliar membrane shape? What is a tonotopic map?
apex = low frequency
base = high frequency
basiliar membrane is coiled up
tonotopic map = frequency map
Structure of the ear via cross section
3 main areas?
at top scala vestibuli scala media scala tympani at bottom
Whats in each of these 3 structures?
scala vestibuli
scala media
scala tympani
SV = perilymph, vestibular membrane, Na+high SM = organ of corti, tectorial membrane, basiliar membrane, stria vascularis(pumps K+ in) = K+ high, endolymph ST= perilymph, Na+ high in here
Organ of corti
hair cells?
membranes at top and bottom?
vibration causes?
inner and outer hair cells
tectorial membrane at top
basiliar membrane at bottom
vibration causes membrane to move up and down, so, the hair-like projections move
Hair cell structure on inner hair cell in organ of corti?
tips of hair linked = so when moved they stretch
made of: stereocilia(actin)
0.3mm diameter
trap door opens and allows movement in (ion channels open)= K+ in to make it depolarised increase K+ INSIDE the cell = -70mv
when moved back = door closes
=this means the membrane potential follows the frequency of sound
Electro-mechanical transduction (sensory) in hair cell
look at picture in notes
Scala media +80mv
HAIR CELL = -45/-70mv high K+
Scala tympani
outside = high K+
action potentials generated and output from bottom
electro-mechanical transduction (amplification)
hair cells generate a mechanical force(from electrical)
jumping hair cells = inner ear amplifier (if an individual can hear = tested by whether you can hear cochlear acoustic emission)
Innervation of ear:
Innervation: inner hair cells in a line (inner receives most nerve inputs)
1 hair cell to 1 nerve because convergence would compromise resolution
lots of nerves with varied thresholds -why? so they can encode a wide range of intensities (so, 1 nerve threshold saturated = move to next nerve)
- feed out directly into higher threshold - hindbrain
-efferent reduces amplification to protect ear (physiological response)
-more noise = more movement in basiliar membrane
Analysis of sound freq intensity sound transduction amplification
freq- (pitch) - encoded in nerves by location along the basiliar membrane
intensity - (loudness) - encoded in nerves by numbers responding and by firing rate
sound transduction - inner hair cells (and Outer)
amplification - outer hair cells
1) cochlear nuclei (CN)
- 3 section?, 3 individual cells and function?
(1st layer of brain associated with hearing - starting from bottom to top)
1) -Anterior Ventral (AVCN), Posterior Ventral(PVCN), Dorsal Regions(DCN) –> each have a tonotopic map
Cells:
1)Spherical and Bushy Cells(VCN) = primary responses
2)Octopus Cells(CN) = onset responses
3)Fusiform cells = pauser responses
-AVCN contains relay cells to media superior Olive - calyx of Held (a giant fast synapse)
2) Superior Olive (SO)
2nd layer of brain associated with hearing - starting from bottom to top
sound localisation
Medial SO - low frequency analysis, interaural time differences, receives faithful inputs from calyx of held on both sides
Lateral SO - high frequency analysis - interaural intensity differences
3) Inferior Colliculus
3rd layer of brain associated with hearing - starting from bottom to top
site of convergence of projections with complex frequency responses
monoaural inputs from DCN - binaural from SO
tonotopic maps
responsible for attention reflexes, startle responses, learned reflexes
4)Cortex
4th layer of brain associated with hearing - starting from bottom to top
tonotopic map retained
neurons with sensitivity to features in complex sounds
auditory space maps, selective attention, inhibition of inappropriate motor responses, recognintion of stimuli, discrimination of temporal patterns and short-term auditory memory
Vestibular system cupula? sacule and utricle? vestibular organs? role of semicircular canals?
cupula = stimulates hair cells as it moves
sacule and utricle = detect gravity changes
semicircular canals role = detect angular movements
vestibular organs = semicircular canals, utricle and sacule
Vestibular Ocular Reflex (VOR)?
allows eye muscles to compensate for head movements
