Session 8

Question 1

What is sound?

Answer 1

A compressive wave travelling at 343m/sec in the air.

Question 2

What is the human auditory range?

Answer 2

20-20,000Hz

Question 3

How does the inner ear allow us to ‘hear’?

Answer 3

Vibrations pass via the ossicles from the tympanic membrane to the oval window. The pressure causes oscillatory movements in the basillar membrane. This induces movement of the stereocilia, causing influx of potassium ions, depolarising the hair celll. This causes a calcium ion influx, resulting in release of the neurotransmitter to the spinal ganglion cells. AP propagates along CNVIII, innervating the cochlear nucleus and auditory brainstem.

Question 4

What is the scala media filled with?

Answer 4

Endolymph

Question 5

What is the scala media bound by?

Answer 5

Vestibular membrane and Basilar membrane.

Question 6

What do the cavities of the bony labyrinth contain?

Answer 6

Perilymph

Question 7

What does the endolymph contain?

Answer 7

High concentration of K+ ions and low concentration of Na+ ions.

Question 8

What structure does the cochlea twist around?

Answer 8

Portion of bone called the modiolus.

Question 9

What are the names of the two perilymph-filled chambers above and below the cochlear duct?

Answer 9

Scale vestibuli and scala tympani.

Question 10

Where is the organ of corti?

Answer 10

Within the cochlear duct, lying on the basilar membrane.

Question 11

What are the two types of hair cells of the organ of Corti?

Answer 11

Inner: senses sound, moves in response to movement of endolymph.
Outer: amplifier. Embedded in the tectorial membrane.

Question 12

Which nerve supplies the receptors of the organ of Corti?

Answer 12

Cochlear nerve

Question 13

What does mechanical displacement of the stereocilia cause?

Answer 13

Influx of potassium ions, depolarising the hair cell. This causes a calcium ion influx, resulting in release of the neurotransmitter to the spinal ganglion cells.

Question 14

What are the two types of spiral ganglion neurones?

Answer 14

Type 1: attached to inner hair cells.

Type 2: attached to outer hair cells.

Question 15

Which hair cells respond to both high and low frequency sound?

Answer 15

Base of basillar membrane = high frequencies.
Apical aspect of the membrane = low frequencies.
This is known as tonotonic distribution of responding receptors.

Question 16

Describe the central auditory pathway.

Answer 16

• Bipolar nerves in the CNVIII pass through the internal acoustic meatus to enter the posterior cranial fossa.
• They synapse with second order neurones in the cochelar nucleus of the medulla and synapse in either the ipsilateral/contralateral superior olivary complex.
• They then go to the inferior colliculus, via the lateral lemniscus.
• Axons then go to the medial geniculate nucleus to the auditory cortex.

Question 17

What is conductive hearing loss? Give two examples.

Answer 17

An issue with transmission of sound from the outer to the inner ear. E.g. otosclerosis, otitis media, blockage in EAM, ruptured tympanic or eustachian tube dysfunction.

Question 18

What is sensorineural hearing loss? Give two examples.

Answer 18

Damage to the cochlea, cochlear nerve or the central auditory pathway. E.g. due to spinal ganglion damage, tinnitus or auditory neuropathy.

Question 19

Give two treatment options for sensorineural hearing loss.

Answer 19

Hearing aids, Cochlear implants, hair cell regeneration, cochlear nucleus implants.