6 - Overview of the Auditory system

Question 1

What is Frequency?

Answer 1

• Pitch
• The number of sound cycles per second activated by the mechanics of the cochlea.

Question 2

What is sound intensity?

Answer 2

• “Loudness”
• The amplitude of the sound wave from peak to peak, achieved by the firing rate of many nerve fibres.

Question 3

What is rapid onset important for?

Answer 3

Localising different sounds and creating a map of the auditory world around us.

Question 4

Where do sound waves travel down and what is their final destination?

Answer 4

They travel down the outer ear to the tympanic membrane.

Question 5

How do the sound waves move across the middle ear?

Answer 5

Via the ossicles.

Question 6

What are the 3 ossicles of the ear?

Answer 6

The malleus, incus and the stapes.

Question 7

Where are the sensory hair cells located in the ear?

Answer 7

The cochlea

Question 8

What are the 3 compartments of the cochlea?

Answer 8

The Scala vestibuli, Scala media and the Scala tympani

Question 9

What does the Scala media contain?

Answer 9

• The organ of corti which has the sensory hair cells.
• Endolymph - high potassium and now sodium

Question 10

What causes high potassium levels in the Scala media?

Answer 10

The cells in the Stria Vascularis

Question 11

What do the Scala vestibuli and Scala tympani contain?

Answer 11

Perilymph - Low potassium and high sodium concentration.

Question 12

What are the inner hair cells?

Answer 12

The main sensory cells of the cochlea.

Question 13

What are outer hair cells important for?

Answer 13

Cochlea amplification.

Question 14

What is tonotopic organisation of the cochlea?

Answer 14

When cells at the base respond to high frequency sounds and at the apex they respond to low frequency sounds.

Question 15

How is cochlear tonotopicity established?

Answer 15

By the basilar membrane travelling sound waves - Sound travels along chambers in the cochlea creating a wave along the basilar membrane from base to apex.

Question 16

What is characteristic frequency (CF)?

Answer 16

The sound of one frequency causing maximal movement of the basilar membrane at one location.

Question 17

How does a lower frequency wave move along the basilar membrane?

Answer 17

• It travels further and causes maximal movement towards the apex.
• The location of the characteristic frequency is also closer to the apex.

Question 18

How does a higher frequency wave travel along the basilar membrane?

Answer 18

• It doesn’t travel as far and causes maximal movement towards the base.
• the location of the characteristic frequency is also closer to the base.

Question 19

How are all hair cells defined?

Answer 19

By the stereocilia hair bundle.

Question 20

What is located within the stereocilia?

Answer 20

• Mechanosensitive ion channels at the tips of the shorter ones.
• Mechanoelectrical transductor channels are connected to the tip links that pull the channels open.
• Voltage gated calcium ion and potassium ion channels.

Question 21

What is the hair bundle bathed in?

Answer 21

Endolymph (The rest is in perilymph)

Question 22

What happens to the inner hair cells during excitatory stimulation?

Answer 22

• A large deflection of the hair cells towards the taller stereocilia, which increases the tension in the tip links.
• Opens the MET channels which causes a large MET current.
• Depolarises the hair cell, potassium moves into the perilymph to help repolarise it.

Question 23

What happens to the inner hair cells during inhibitory stimulation?

Answer 23

• A large deflection of the hair bundle back towards the shorter stereocilia.
• the tip links slacken and the MET channels close and turn off.
• The cell gets hyperpolarised below the resting potential so there is little to no neuronal activity.

Question 24

What happens to the inner hair cells during sustained stimulation?

Answer 24

• The sustained sound moves the hair bundle back and forth at the sound frequency.
• Generates pulses of neurotransmitter activity and release.

Question 25

What is electromobility?

Answer 25

A function that outer hair cells have which makes them shorten and lengthen with sound frequency.

Question 26

What is prestin and where is it located?

Answer 26

The molecule that allows the cell to shorten and lengthen in response to changes in membrane potential. Its located in the membrane of outer hair cells.