Physiology of Hearing

Question 1

Which parts of the external ear are involved in hearing and how do they work?

Answer 1

Pinna - amplifies and channels sound down internal acoustic meatus (10dB)

Helix/Antihelix → Concha

Tragus/Antitragus → External Acoustic Meatus

Question 2

What are the two functoins of the middle ear for hearing?

Answer 2

Amplifies sound

Converts sound → mechanical energy

Question 3

How does the middle ear convert sound to mechanical energy?

Answer 3

1. Sound waves hit the Tympanic membrane → Vibration
2. Malleus (attached to ear drum) vibrates and hits the incus
3. Incus acts as a level on stapes
4. Stapes has a footplate on the oval window → pressure waves in fluid

Question 4

How does the middle ear amplify sound?

Answer 4

The size ratio between the Tympanic membrane:Stapes footplate → energy focussed on small area

Leverage - malleus and incus rotate around fulcrums to magnify force

Conversion of energy - no air/fluid interface loss

Question 5

Image of the outer, middle and inner ear

Answer 5

Question 6

Which part of the temporal bone does the bony labyrinth sit?

Answer 6

Otic capsule

Question 7

What is included in the bony labyrinth?

Answer 7

Spiral canal:

1. Scala Vestibuli - Vestibular duct
2. Scala Media - Cochlear duct
3. Scala Tympani - Tympanic duct

Semicircular canals

Vestibule

Question 8

What is the fluid in the bony labyrinth called?

Answer 8

Perilymph - High Na and Low K

Question 9

Name the 4 membrane encased ducts/sacs of the membranous labyrinth

Answer 9

Cochlear Labyrinth/Scala media/Cochlear duct

Vestibular Labyrinth - utricle and saccule

Semicircular ducts

Vestibular acqueduct and endolymphatic sac

Question 10

What fluid does the membranous labyrinth contain? Where is it produced? and where does it drain?

Answer 10

Endolymph - High K and Low Na

Produced at apex of cochlea (Stria Vascularis) and vestibular labyrinth

Drains via vestibular acqueduct through internal auditory meatus to endolymphatic sac

Question 11

Diagram of cross section of spiral canal

Answer 11

Question 12

Where would a high frequency wave cause displacement of the scala media?

Answer 12

High frequency - Close to oval window

Low frequency - displacement further from oval window

Question 13

What is responsible for the conversion of waves to neuronal signals?

Answer 13

The organ of Corti

Question 14

Where is the Organ of Corti place? and how does it convert waves to neuronal signals?

Answer 14

It is located on the basilar membrane of the scala media

Waves → movement of the tectorial membrane → hairs

Impulses → Vestibulocochlear nerve → Auditory cortex

Question 15

What happens in the scala tympani?

Answer 15

The waves travel back down the scala tympani to the round window and dissipate in the air of the middle ear