auditory introduction

Question 1

Why is sound sensation important?

Answer 1

Early mammals were small and nocturnal
Triggers emotions
Communication, recognise different sounds, topographic view on auditory world
Survival

Question 2

What is Tonotography?

Answer 2

relating to or being the anatomic organization by which specific sound frequencies are received by specific receptors in the inner ear with nerve impulses traveling along selected pathways to specific sites in the brain

in the cochlear - the base responds to high frequency , apex to low frequency

Question 3

how is Sound Frequency achieved and what the units

Answer 3

(Pitch) - Hz

• A wide range of sound frequency has to be covered (x103).
• Achieved by cochlear mechanics and physiology of hair cells

Question 4

how is Sound Intensity (Loudness) achieved and what is it measured in

Answer 4

– dB

A huge range of sound intensity has to be encoded

Question 5

How does sound travel along the auditory pathway?

Answer 5

Sound enters ear, travels along the auditory canal hitting the tympanic membrane causing it to move backwards and forwards. This moves the ossicles of the middle ear causing the Oval window to move backwards and forwards causing fluid movement in the cochlear.

Question 6

What are the three ossicles?

Answer 6

Malleus, incus and stapes

Question 7

What is the function of the cochlea?

Answer 7

Contains sensory hair cells and nerve fibres that transmit the sound to the brain at a neuronal signal.

Question 8

What does the cochlear consist of? and What are the three compartments inside the cochlear?

Answer 8

Three separate chambers which form the spiral of the cochlea travelling from the base to the apex.

Scala vestibuli – filled with perilymph, 0mV
Scala media – filled with endolymph, 80mV – active pumping from cells
Scala tympani – filled with perilymph, 0mV

Question 9

Describe perilymph

Answer 9

Similar of ECF
Low potassium
Normal calcium

Question 10

Describe endolymph

Answer 10

High potassium concentration – positive potential

Low calcium

Question 11

Why does the Scala Media have a high K concentration and what does this create

Answer 11

because of active pumping from cells in the Scala vascularis.

creates a positive potential in this compartment compared to the Scala vestibuli and Scala tympani.

Question 12

What is the endocochlear potential?

Answer 12

80 mV

Question 13

What is the cochlear innervated by?

Answer 13

The auditory nerve

Question 14

What is the organ of Corti? Where is it? what does it contain and its membrane potential?

Answer 14

The main sensory receptor – contains auditory receptors.

situated on the basilar membrane in one of the three compartments of the Cochlea.

It contains four rows of hair cells which protrude from its surface.

60 mV

Question 15

What is the function of the inner hair cell of the cochlear?

Answer 15

The main sensory receptors of the cochlear

Question 16

What is the function of the outer hair cell of the cochlear? How many rows are there?

Answer 16

It’s the cochlear amplifiers

3 rows

Question 17

What are stereocilia?

Answer 17

Projections in the top of OHC and IHC and contact the tectorial membrane

Question 18

How has Tonotopicity been preserved?

Answer 18

A linear gradient of sound frequency is preserved in

Question 19

how does sound enter the cochlear and what does it create

Answer 19

Sound vibrations enter the cochlear as a pressure wave that travels along the diff compartments from the base of the cochlear to the apex – creating a wave along the basliar membrane that causes a maximal movement that corresponds to the freq of sound – called characteristic freq.

Question 20

what is the structure of the basilar membrane and how does this determine frequency

Answer 20

the width and stiffness of the basilar membrane – narrow and stiff at base and wider and more flexible at apex.

So high sound freq causes a peak movement towards base of the cochlear and lower freq cause a peak at the apex.

Question 21

How far does low frequency sound travel along the Basliar membrane and what does this cause?

Answer 21

The lower frequency sound travels further along the baslier membrane causing a peak towards apex of cochlear.

Question 22

How far does high frequency sound travel along the Basliar membrane and what does this cause?

Answer 22

The higher frequency sound doesn’t travel so far and causes a maximal movement towards the base.

Question 23

State the properties of the general hair cell found in auditory and vestibular system

Answer 23

• Stereocilia hair bundle
• Mechanoelectrical transducer channels (MET)
• Voltage-gated Ca channels
• Voltage-gated K channels
• Nerve fibres

Question 24

How are all hair cells defined by? and How are the mechanoelectrical transducers channels connected to taller rows?

Answer 24

The stereocilia hair bundle that project from apical surface
MET located on tips of the shorter rows of stereocilia

connected By tip links

Question 25

what is the function of tip links?

Answer 25

When force is applied, they pull open the MET channels allowing current into the hair cell

Question 26

What does slight tension on tip links lead to?

Answer 26

Few are open leading to inwards resting transducer current carried by K ions - which depolarises inside of hair cell slightly giving it a more depolarised resting membrane potential.

Question 27

How is K able to enter the hair cell?

Answer 27

K able to enter cell down the electrical gradient due to the high K concentration in endolymph and difference in potential in between the Scala media and inside of the cell.

Question 28

What solution surrounds the apical surface of hair cells and stereocilia? What solution surrounds the base of the hair cell?

Answer 28

What solution surrounds the apical surface of hair cells and stereocilia? Endolymph What solution surrounds the base of the hair cell? Perilymph

Question 29

What does the slightly depolarised resting potential of general hair cells activate? What does this lead to? What is it called?

Answer 29

Activates some Ca channels and leads to a resting action potential firing rate in the nerve fibres called the spontaneous rate

Question 30

State the properties of an excitatory deflection of a general hair cell

Answer 30

- Large deflection of the hair bundle - Maximal tip link tension - Large MET current - Fully depolarises hair cell - Rapid train of action potentials

Question 31

What does depolarisation of a general hair cell activate and what does this cause?

Answer 31

Depolarisation activates the Ca channels and increases neurotransmitter release and action potential frequency in the nerve fibre. Also activates K channels that allow K ions out the cell – helps to repolarise the hair cell back to resting potential.

Question 32

State the properties of an inhibitory deflection of general hair cells

Answer 32

- Large deflection of the hair bundle in opposite direction - Minimal tip link tension - No MET current - Fully hyperpolarises hair cell below resting potential No or very few action potentials

Question 33

State properties of Outer hair cells (OHCs)

Answer 33

- V-shaped hair bundle - Majority of nerves contacts are efferent fibres - Prestin in cell membrane required for electromotility