Cochlea and auditory system

Question 1

what type of receptors?

Answer 1

mechanoreceptors

Question 2

What is sound?

What does SPL mean?

Answer 2

a compression wave = moves back and forwards

SPL = sound pressure level

Question 3

What does frequency mean?

What does amplitude mean?

Answer 3

how often

sound intensity

Question 4

Route of sound?

Answer 4

ear canal to ear drum = well adapted to transmitting frequency

Question 5

why have 2 ears?

Answer 5

localising sounds

Question 6

What is found in the outer ear?

Answer 6

auricle, external auditory canal, ear drum

Question 7

What is found in the middle ear?

Answer 7

temporal lobe of brain, temporal base, hemmar, anvil, stirrup

Question 8

What is found in the inner ear?

Answer 8

semicircular canals, oval window, cochlea, round window, nerves, eustachian tube

Question 9

Tympanic membrane?

Answer 9

eardrum
includes: malleus, stapes and incus (all behind)
(at footplate of the stapes is the oval window)

Question 10

Simple resonance model?
near apex = high or low freq?
near base = high or low freq?
basiliar membrane shape?
What is a tonotopic map?

Answer 10

apex = low frequency
base = high frequency
basiliar membrane is coiled up
tonotopic map = frequency map

Question 11

Structure of the ear via cross section

3 main areas?

Answer 11

at top
scala vestibuli 
scala media
scala tympani 
at bottom

Question 12

Whats in each of these 3 structures?
scala vestibuli
scala media
scala tympani

Answer 12

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

Question 13

Organ of corti
hair cells?
membranes at top and bottom?
vibration causes?

Answer 13

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

Question 14

Hair cell structure on inner hair cell in organ of corti?

Answer 14

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

Question 15

Electro-mechanical transduction (sensory) in hair cell

Answer 15

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

Question 16

electro-mechanical transduction (amplification)

Answer 16

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)

Question 17

Innervation of ear:

Answer 17

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

Question 18

Analysis of sound
freq
intensity
sound transduction
amplification

Answer 18

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

Question 19

1) cochlear nuclei (CN)
- 3 section?, 3 individual cells and function?

(1st layer of brain associated with hearing - starting from bottom to top)

Answer 19

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)

Question 20

2) Superior Olive (SO)

2nd layer of brain associated with hearing - starting from bottom to top

Answer 20

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

Question 21

3) Inferior Colliculus

3rd layer of brain associated with hearing - starting from bottom to top

Answer 21

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

Question 22

4)Cortex

4th layer of brain associated with hearing - starting from bottom to top

Answer 22

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

Question 23

Vestibular system
cupula?
sacule and utricle?
vestibular organs?
role of semicircular canals?

Answer 23

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

Question 24

Vestibular Ocular Reflex (VOR)?

Answer 24

allows eye muscles to compensate for head movements