Topic Eight - The Cochlear

Question 1

Complete the cochlear kahoot*

Question 2

How is endolymph produced and which scalae does it occupy?*

Answer 2

• Endolymph is produced by the stria vascularis in the cochlear and the dark cells of the vestibular labyrinth
• Endolymph has a high potassium content, low sodium
• Endolymph occupies the scala media

Question 3

How is perilymph produced and which scalae does it occupy?*

Answer 3

• Perilymph is a mixture of filtrations from cerebrospinal fluid and from blood vessels in the ear
• Blood is the most important source
• Perilymph occupies both the scala vestibuli and the scala tympani
• Perilymph has a high sodium concentration, low potassium concentration

Question 4

What is the role of the outer hair cells in the the transduction of sound?*

Answer 4

The outer hair cells reduce dampening and increase the vibration of the basilar membrane by a factor of 1000.

3 rows of outer hair cells (up to 4-5 rows in the apical end).

The outer hair cells preform MET and EMT (electromechanical transduction). EMT is the production of movement in response to electrical changes.

Question 5

What is the role of the inner hair cells in the the transduction of sound?*

Answer 5

The inner hair cells detect the vibration of the basilar membrane and release packets of neurotransmitter onto the below neurons.

There is one row of inner hair cells.

They preform mechanoelectrical transduction (MET).

Question 6

What is the role of the primary afferent neurons in the the transduction of sound?*

Answer 6

Once the inner hair cells have released the neurotransmitters, action potentials are triggered in the primary afferent neurons.

The action potentials then send signals to the brain via the VIII cranial nerve.

95% of the primary afferent neurons synapse with the inner hair cells, compared to 5% of the outer hair cells.

Question 7

What is the role of the tectorial membrane in the the transduction of sound?*

Answer 7

Acellular structure that overlays the outer hair cells.

Vital for providing a radial shear to the outer hair cells in response to the movement of the basilar membrane. This allows the ion channels to open.

Question 8

What is the role of the supporting cells in the the transduction of sound?*

Answer 8

Deiter’s/phalangeal cells:
- Provide structural support to the outer hair cells from underneath

Other supporting cells:
- Evidence to suggest they play a role in fluid and ion balance within the cochlear.
- In non-mammalian animals, supporting cells can play a role in the regeneration of hair cells.