Neuro - Auditory System

Question 1

What are the functions of the outer ear?

Answer 1

To capture sound and to focus it to the tympanic membrane
To amplify some frequencies by resonance in the canal
To protect the ear from external threats

Question 2

What is the main function of the middle ear?

Answer 2

Amplification by:

1) Focusing vibrations from a large surfaces area to a smaller surface area - causes an increased pressure
2) using leverage stapes to increase the force on the oval window

Question 3

What is the function of the inner ear?

Answer 3

To transducer vibration into nervous impulses

Question 4

How is the basilar membrane arranged?

Answer 4

Tonotopically - like a xylophone, thinner on one end and wider on the other

Question 5

What type of hair cells are present in the organ of corti?

Answer 5

Inner and outer hair cells

Question 6

What do the inner hair cells do?

Answer 6

Carry 95% of the afferent information of the auditory nerve and their function is the transduction of the sound into nerve impulses

Question 7

What do the outer hair cells do?

Answer 7

Carry 95% of the efferent information of the auditory nerve. Their function is the modulation of the sensitivity of the response.

Question 8

How does the outer hair cell modulate the sensitivity of a response?

Answer 8

The outer hair cells contract or extend to lower or raise the tectorial membrane above the inner hair cells and gene contact of the tectorial membrane is what causes the depolarisation of the cell

Question 9

How does transduction of a vibration lead to a nerve impulse being generated?

Answer 9

1) Deflection of the stereocilia - hairs on the end of individual hair cells - towards the longest cilium will open K+ channels
2) K+ enters the main hair cell and causes depolarisation
3) This releases excitatory neurotransmitters - believed to be glutamate
4) The neurotransmitter goes to the afferent nerve and sends a impulse to the CNS

Question 10

How do larger vibrations cause a greater amplitude?

Answer 10

The larger vibration causes a greater deflection of the stereocilia, as more cells will be in contact with the tectorial membrane, which allows for more K+ to enter the hair cell and depolarise it more, releasing more excitatory neurotransmitter

Question 11

What is the pathway of the nerve impulse from the cochlea?

Answer 11

Cochlea 
Cochlea nucleus
Superior olive
Inferior colliculus
Medial geniculate body
Auditory cortex

Question 12

What is the aim of a hearing assessment?

Answer 12

If there is hearing loss to determine:

To what degree and what type

Question 13

What types of hearing loss are there?

Answer 13

Conductive - problem in the outer or middle ear

Sensorineural - problem is in the inner ear or auditory nerve

Mixed - conduction and transduction of sound are affected, problem affects more than one part of the ear

Question 14

What can cause conductive hearing loss?

Answer 14

If outer ear:
Wax
Foreign body

If middle ear:
Otitis
Otosclerosis

Question 15

What can cause sensorineural hearing loss?

Answer 15

If inner ear:
Presbycusis - most common
Ototoxicity

If auditory nerve:
VIII nerve tumour

Question 16

What treatment can be given for hearing loss and how do they work?

Answer 16

Trust underlying cause - e.g. remove ear wax or foreign body in outer ear

Cochlear implants - for dead cells, replaces the function of the hair cells apparent, analysing it, transform it into electrical signals and send an electrical impulse, needs a functional auditory nerve

Hearing aids - for dead cells, amplify the sound, do not replace any structures

Brainstem implants - nerve is the issue, similar to cochlea implant but instead of the electrical signal going to the cochlea it goes to the brain directly, last option for Patients