Cochlear and hearing

Question 1

What are are the 3 chambers of the cochlear and what substances do they contain?

Answer 1

1) Scala vestibuli
- Perilymph

2) Scala media
- Endolymph

3) Scala tympani
- Perilymph

Question 2

What is the stria vascularis?

Answer 2

Cells which pump K+ into the endolymph in the scala media

Question 3

What is the organi of corti?

Answer 3

Auditory sensory organ, located on the basilar membrane

Question 4

What is the potential of the endolymph compared to the perilymph?

Answer 4

+80mV

Question 5

What does the endolymph surround?

Answer 5

The hair bundles

Question 6

What does the perilymph surround?

Answer 6

The cell body and the glutamate synapse onto the primary afferent neuron

Question 7

What are the different parts of the organ of corti?

Answer 7

1) Tectorial membrane
- Above the hair cells

2) Basilar membrane
- Below the cells

3) 1 row of inner hair cells
4) 3 rows of outer hair cells

Question 8

What causes the movement of the basilar membrane?

Answer 8

• Waves of fluid created by the stapes hitting the oval window

Question 9

What do different frequencies of sound cause the basilar membrane to do?

Answer 9

• Maximum displacement at different regions of the membrane
• Low frequency = base (membrane is thick and stiff)
• High frequency = apex (membrane is thin and wide)

Question 10

What happens to the outer hair cells when the basilar membrane moves upwards and why?

Answer 10

• The tip-links (which connect the hair bundles together) become stretched as the hair cells move towards the TALLEST sterocillia
• This is because the tallest sterocillia is connected to the tectorial membrane, which doesn’t move
• Positive ion channels open, depolarisation
• Na+ channels open
• Ca2+ channels open

Question 11

What happens to the outer hair cells when they are activated and what does this allow?

Answer 11

• Activate a protein
• Causes contraction of the outer hair cells (become shorter)
• Amplifies the movement of the basilar membrane
• Inner hair cells can respond to smaller amplitudes

Question 12

What causes the inner hair cells to be activated?

Answer 12

Fluid movement distorting the hairs

Question 13

When does the basiliar membrane move upwards?

Answer 13

• During RAREFIED air

- Stapes moves outwards

Question 14

What is in the outer ear?

Answer 14

• Pinna

- Auditory canal

Question 15

What is in the middle ear?

Answer 15

• Tympanic membrane

- Ossicles (malleus, incus and stapes)

Question 16

What is in the inner ear?

Answer 16

• Oval window and cochlear

Question 17

How does sound travel to the inner ear?

Answer 17

• Down the auditory canal
• Causes vibration of the tympanic membrane
• Causes vibration of the ossicles
• Causes vibraion of the oval window

Question 18

What is the purpose of the ossicles?

Answer 18

• Concentrate pressure from the tympanic membrane onto the oval window
• As going from air filled to fluid-filled, need a higher pressure to to overcome the resistance of the fluid behind the oval window

Question 19

What is the connection between the malleus and incus?

Answer 19

Ridgid

Question 20

What is the connection between the incus and stapes?

Answer 20

Flexible

Question 21

What are alternative names for the malleus, incus and stapes?

Answer 21

Hammer
Anvil
Stirrup

Question 22

What is the round window?

Answer 22

• Helps relieve the pressure in the middle ear when the stapes is pushed into the oval window

Question 23

What is the oval window connected to?

Answer 23

The scala vestibuli

Question 24

What is the round window connected to?

Answer 24

The scala tympani

Question 25

What happens in the middle ear during compression of the wave?

Answer 25

• Inward movement of tympanic membrane
• Mallues and incus move upwards
• Stapes move into the oval window
• Round window open