Chapter 8 - Auditory Senses

Question 1

Where are high and low frequencies detected in the cochlea and what causes this?

L8 S15

Answer 1

High frequencies:

• closer to oval window
• short, stiff fibers

Low frequencies:

• closer to helicotrema
• long, limber fimbers

Basilar fibers in organ of Corti get longer and decrease in diameter as they move away from the oval window and approach the helicotrema.

Question 2

How does a hair cell generate a local potential to stimulate the cochlear nerve?

Answer 2

Movement of the basilar fiber causes movement of the reticular lamina which hair cells are tightly associated with.
A shearing force is generated on the hair cells against the tectorial membrane.
Cilia on the hair cells are bent causing potassium channels to open and depolarize the hair cells.

Question 3

Describe the properties of endolymph and perilymph.
What part of hair cells are in contact with each fluid and how does this help generate a local potential.

L8 S22

Answer 3

Endolymph:

• scala media
• high concentrations of potassium; low concentration of sodium

Perilymph:

• scala vestibuli and scala typmani
• high concentrations of sodium; low concentration of potassium

There is a potential difference between these two fluid of +80mv. The top of hair cells are in contact with endolymph while the bottom is in contact with perilymph.