cochlear and auditory system

Question 1

sound

Answer 1

mechanical energy causing vibrations detected by the ears

Question 2

compressed air

Answer 2

dense particles (peak)

Question 3

rarefied air

Answer 3

less dense particles (trough)

Question 4

frquency

Answer 4

how many peaks (compressed) and troughs (rarefied) within a second 1 peak in 1 second= 1 hertz

Question 5

decibel scale is a

Answer 5

logarithmic scale

Question 6

intensity /amplitude

Answer 6

Air pressure difference between peaks and troughs, expressed as decibels (dB)

Question 7

physioloical ranges of freq and intenisy for humans

Answer 7

Don’t have the same threshold of frequency for every sound
100-10,000 hertz for speech
Average of speech 60 DBs
Anything above 100dbs is damaging to ears

Question 8

human hearing range

Answer 8

20Hz to 20,000 Hz

Question 9

pinna

Answer 9

outer ear (latin for wing)
more sensitive to sounds from in front than behind

localisation of sound from above or below (vertical)

//AKA oricle

Question 10

after pinna sound goes

Answer 10

down the extnerla auditory cancel through bone of skull until it hits tympanic membrane (drum)

Question 11

middle ear

Answer 11

vibration movesback and forth on drum causing oscillations on oval window (much smaller)- bottom of cochlea
oval window movement makes fluid move in cochlea

Question 12

the ossicles of the middle ear

Answer 12

latin for ‘little bones’

hammer, anvil and stirrup

Question 13

malleus to incus

Answer 13

has a rigid connection (have to move together)

Question 14

incus to stapes

Answer 14

has a flexible connection (important for how sound moves are transferred through middle ear)

Question 15

how the middle ear transfers sound

Answer 15

Sound wave is spread out across quite wide area of tymp drum
Oval window is 20x smaller than tymp drum (so the pressure would be much more concentrated)
Middle ear concentrates the sound onto the oval window – it is amplified
Important because moves from air filled env in middle air to fluid filled env in cochlea
There is more resitsant at back of oval window than the tymp mem
Pressure is relived from the cochlea on the round window (because cochlea is sealed)

Question 16

high pitch

Answer 16

high freq

Question 17

low pitch

Answer 17

low freq

Question 18

volume

Answer 18

amplitude

Question 19

extnerl and middle ear

Answer 19

only used for hearing

Question 20

inner ear

Answer 20

for hearing and maintaining equilibrium

Question 21

tympanic membrane

Answer 21

ear drum

boundary between external and middle ear

Question 22

Impedance matching

Answer 22

air and water have different impedances i.e. the tendency of each medium to oppose movement brought about by a pressure wave.

Question 23

when sound comes through ear

Answer 23

the ear drum vibrates
goes through to bones (ossicles)
these amplify the sound waves
tympanic cavity focuses pressure of sound waves so they’re strong enough to move fluid in inner ear

using osicle bones- malleus (hammer), incus (anvil) and stapes (stirrup)

these project vibrations to another membrane - the superior oval window- setting the fluid in inner ear into motion

waves transduced into electrical signals

cochlea 3 layers (scale vestibulili, scala media, scala tympani)

the basilar membrane vibrates at different pitches along it’s length

base - high freq and
apex- low freq

organ of court gets tickled with hair cells
when triggered opens mechanically gated sodium channels

this influx causes graded potentials, if enough an action potential 
to CNS (vai cochlear nerve, auditory pathway, and cortex)

Question 24

how does the brain know the sound

Answer 24

detects pitch of sound based on location of hair cells being triggered

loud sound=more movement=more frequent AP

Question 25

how does basil membrane displacement affect hair cells

Answer 25

stapes moves outward
basilar membrane moves upwards
hair cells depolarise
(out and up- depolarise)

stapes moves inward
basilar membrane moves donwards
hair cells hyperpolarise
(in and down - hyper polarise)

Question 26

hair bundles are connected by

Answer 26

tip links

hair bundles are surrounded by endolymph within the scala media
mechanoelectrical transducer channel

Question 27

inner hair cells - the primary sensory receptors

Answer 27

Apical at the top – surround by endolymoh (high na) and positive potential (80mv more positive than perilymph)
Forces positive ions to move from endo to perilymp via hair cells
And can only do that when channels in hair cell bundles are open
High potassium moving into the hair cell makes it more positive and leave via other channels in side
Depolarization of K moving in open voltage gated calcium channels
At the base of the cell calcium comes in and causes release of synaptic vesicles with glutamate (excitatory)
Glutamate crosses synapse and activates AMPA or the other one it binds to
Causing ESPs — AP to auditory brain stem

Question 28

endolymph

Answer 28

higher K+

+80mv

Question 29

perilymph

Answer 29

low K+

0Mv

Question 30

outer hair cells are electromotile

Answer 30

act as the cochlear amplifier

OHCs change in size when bundles are stimulated

BM moves upwards
hair bundles move towards taller stereo cilia
OHC depolarises
OHC contracts
OHC becomes shorter 
amplifies upwards movement of BM