Physiology of hearing and balance

Question 1

What range of frequency can humans hear?

Answer 1

20Hz to 20000Hz

Question 2

How does the internal surface of the tympanic membrane maintain atmospheric pressure?

Answer 2

Via the eustachian tube which is in contact with the nasopharynx (air at atmospheric pressure can then travel up and equalise the two sides of the tympanic membrane)

Question 3

Describe the chain of events that allow the middle ear to amplify sound

Answer 3

1. Tympanic membrane vibrates in response to sound waves
2. Causes malleus to vibrate, which hits the incus, which hits the stapes which then hits the oval window (the entrance to inner ear) All the bones are then vibrating at the same frequency.. But, since the surface area is much smaller than the surface area of the tympanic membrane then the pressure is increased. The lever action of the ossicles has also increased the pressure (amplitude) This is needed to transmit the sound through liquid.

Question 4

By approximately how much does the sound pressure increase via the actions of the ossicles?

Answer 4

22x

Question 5

What two muscles are responsible for opening the eustachian tube?

Answer 5

Tensor veli palatine

Levator palatine

Question 6

What are the three compartments of the cochlea?

Answer 6

Cochlear duct/Scala media
Upper compartment/Scala vestibuli
Lower compartment/Scala tympani

Question 7

Which structures of the cochlea contain endolymph?

Answer 7

The middle compartment ONLY

Question 8

What structures of the cochlea contain perilymph?

Answer 8

Upper and lower compartments

Question 9

What is the specific organ of hearing and where is it found?

Answer 9

The organ of corti

Found on the basilar membrane of the scala media

Question 10

Describe how the organ of corti works?

Answer 10

The organ of corti contains hair cells which are the receptors for sound.

1. The action of the stapes hitting the oval window causes vibration of the cochlea and displacement of the fluid within.
2. The basilar membrane of the middle compartment presses against the hair cells of the organ of corti. The movement of the hairs causes neuronal signals to be fired.

Question 11

What is the role of the inner hair cells of the organ of corti?

Answer 11

Transformation of the mechanical forces of sound into the electrical impulses of hearing. The back and forth mechanical deformation of these cells causes depolarisation and repolarisation. Depolarization increases the rate of neurotransmitter firing.

Question 12

What do the outer hair cells of the organ of corti do?

Answer 12

Enhance the response of the inner hair cells, making them more sensitive, but do not actually send neuronal signals themselves.

Question 13

What part of the cochlea is sensitive to high pitched sound?

Answer 13

The narrow end nearest the oval window

Question 14

Which part of the cochlea is sensitive to low pitched sounds?

Answer 14

The wide end nearest the helicotrema

Question 15

How are stereocilia in the organ of corti arranged?

Answer 15

In height order with the tip links connecting them together.

Question 16

When does depolarisation of the hair cells in the organ of corti occur?

Answer 16

When the cells are deflected towards the longest

Question 17

When does hyperpolarisation of the hair cells in the organ of corti occur?

Answer 17

When hairs are deflected away from the longest hair.

Question 18

Name the two otolith organs?

Answer 18

Saccule and utricle

Question 19

What do the otolith organs detect?

Answer 19

Changes in linear motion

Question 20

Describe how the utricle detects changes in movement.

Answer 20

They contain receptive hair cells which sit on a gelatinous layer containing calcium carbonate crystals. When a person is sitting upright the hairs within the utricle are orientated vertically. Moving your head in a position that isn’t vertical causes displacement of the crystals die to gravity and then to bending of the hair cells. (hyperpolarization or depolarization)
This information is then taken by the vestibular nerve to the CNS

Question 21

What is the position of hairs in the utricle when a person is upright?

Answer 21

Vertical

Question 22

What is the position of hairs in the saccule when a person is sitting upright?

Answer 22

Horizontal

Question 23

Describe how the saccule detects changes in movement.

Answer 23

Moving in a position other than horizontal (eg getting out of bed) causes displacement of calcium carbonate crystals and depolarization or hyperpolarization of hair cells causes action potentials to fire.

Question 24

What otolith organs would respond to standing from a lying position?

Answer 24

Saccule

Question 25

What otolith organ would respond to tilting your head to the side?

Answer 25

Utricle

Question 26

Whereabouts in the brain is information from the otolith organs integrated with input from the other sense organs?

Answer 26

The cerebellum

Question 27

What sort of movement do the semi circular canals detect?

Answer 27

Rotational acceleration or deceleration (CHANGES in movement)

Question 28

Where do they receptive hair cells of the semi circular canals sit?

Answer 28

The ampulla

Question 29

What fluid is within the semi circular canals?

Answer 29

Endolymph

Question 30

What is the gelatinous layer called that the hairs in the semi circular canals sit in?

Answer 30

The cupula