Auditory System

Question 2

Lecture 1

Answer 2

Cochlea and the Organ of Corti

Question 3

What are decibels?

Answer 3

Units of sound pressure/loudness.

Question 4

What are the components of the outer ear?

Answer 4

External auditory canal. Eardrum.

Question 5

What are the components of the middle ear?

Answer 5

Malleus. Incus. Stapes. Eustachian tubule.

Question 6

What are the components of the inner ear?

Answer 6

Semi-circular canal. Auditory canal. Cochlea. Vestibular nerve. Endolymphatic sac.

Question 7

What are the 3 chambers of the cochlea?

Answer 7

Scala Vestibuli. Scala Media. Scala Tympani.

Question 8

How is the scala media different to the other two chambers?

Answer 8

High concentration of potassium ions.

Question 9

What are the components of the Organ of Corti?

Answer 9

Outer hair cells. Inner hair cells. Tunnel of Corti. Spiral limbus. Inner spiral sulcus. Outer spinal sulcus. Tectorial membrane. Hensen’s cells. Claudius’ cells. Deiter’s cells. Reticular lamina.

Question 10

What are the main functional components of the Organ of Corti?

Answer 10

Hair cells.

Question 11

Describe the signal transmission in the Organ of Corti.

Answer 11

If hair cells bend towards Kinocillium they depolarise. If hair cells bend away from Kinocillium they hyperpolarise the cell. The signal is then sent to the spiral ganglion in the mediolus.

Question 12

Describe the organisation of hair cells in the Organ of Corti.

Answer 12

3 rows of outer and 1 row of inner hair cells. All oriented in the same direction. Joined by tiplinks for unidirectional movement.

Question 13

Lecture 2

Answer 13

Hair cells

Question 14

Describe the innervation pattern of hair cells.

Answer 14

3000 hair cells in cochlea. 33,000 cells in spiral ganglion. 90% of afferent ganglion fibres innervate the inner hair cell row.

Question 15

Why are hair cells innervated with efferent fibres?

Answer 15

Tuning.

Question 16

What is the structure of the basilar membrane?

Answer 16

Made up of collagen fibrils. Connected to cochlea via rounf window. High freq. at the beginning; low at the end. Terminates at its helicotrema.

Question 17

What is a resonant frequency?

Answer 17

Frequency at which an object vibrates. Different in different regions of cochlea.

Question 18

What is the role of the tectoral membrane?

Answer 18

Pushes on hair cells upon deflection of the basilar membrane.

Question 19

What is the resting potential of hair cells?

Answer 19

minus 52mV

Question 20

How are hair cells tuned?

Answer 20

Mechanically via length of hair bundle. Electrically via sinusoidal potential response.

Question 21

Describe the steps of sinusoidal membrane potential changes in hair cells.

Answer 21

Potassium influx caused by bending of hair towards Kinocillium. Calcium influx causes rise in intracellular Ca2+ and mitochondrial uptake of Ca2+. Activation of calcium sensitive potassium channels causes potassium efflux. Further efflux by potassium VGCs. Efflux of calcium via the calcium pump.