21: Hearing

Question 1

What are zones of high pressure in the air

Answer 1

Zones of compression

Question 2

What are zones of low pressure in the air

Answer 2

Zones of refraction

Question 3

What are the two forms of sound that we are able to detect?

Answer 3

The amplitude and the pitch

Question 4

Describe to impact of the threshold of hearing

Answer 4

• Our receptors for sound are more responsive when we are young
• We are most sensitive to sounds about 500-3000hertz
• Hearing is optimised in the range of the sound of human speech

Question 5

(Brief) discription of the movement of soundwaves to ear

Answer 5

External auditory canal (outer ear/pinna) –> tympanic membrane (eardrum) –> middle ear cavity –>inner ear (cochlea)

Question 6

What is the role of the outer ear (pinna) and the external auditory canal?

Answer 6

Can help to amplify and direct the soud

Question 7

What is the role of the tympanic membrane? (eardrum)

Answer 7

• Vibrates at the same frequency as the sound wave

- It separates the external auditory canal from the middle ear

Question 8

What is the inner ear/cochlea?

Answer 8

-Fluid-filled, spiral-shaped passage in the temporal lobe

Question 9

What are the two main roles of the cochlea?

Answer 9

• Hearing

- Vestibular (balance)

Question 10

What is the role of the three small bones: the malleus, incus and stapes (in the inner ear)

Answer 10

Since the inner ear is filled with fluid, and liquid is more difficult to move compared to air, the sound pressure transmitted to the inner ear must be amplified.

These bones act as a piston and couple the vibrations of the tympanic membrane to the oval window

Question 11

What are the three chambers of the cochlea?

Answer 11

• Upper chamber: Scala Vesticuli
• Middle chamber: Scala Media
• Lower chamber: Scala Tempani

Question 12

What fluid is the scala vesticuli filled with?

Answer 12

Perilymph, which has a composition similar to ECF

Question 13

What fluid is the scala media filled with?

Answer 13

Endolymph, which has a composition similar to ICF

Question 14

What chamber of the cochlea does signal transduction occur in?

Answer 14

Scala Media

Question 15

Where is chamber of the cochlea is the organ of corti present in?

Answer 15

Scala Media

Question 16

Describe the receptor cells of the organ of corti

Answer 16

They are hair cells. They are mechanoreceptors that have hairlike stereocilia protruding from one end

The hair cells transform the pressure waves in the cochlea into receptors for potential

Question 17

Where are the hair cells of the organ of corti attached to?

Answer 17

They are attached to the basilar membrane which stimulate the hair cells

Question 18

Where is the stereocilia of the hair cells of the organ of corti in contact with>

Answer 18

Tectorial membrane, which overlies the organ of corti

Question 19

What fluid is the scala tempani filled with?

Answer 19

It is filled with the fluid perilymph which has a composition similar to ECF

Question 20

Describe the movements transmitting sound vibrations through the middle and inner air (air to fluid)

Answer 20

1. Tympanic membrane deflects
2. Middle ear bones move
3. Membrane in oval window moves
4. Basilar membrane moves

Question 21

Describe the tuning of the basilar membrane

Answer 21

• Low frequency when it is far from the basilar membrane

- High frequency when it is close to the basilar membrane

Question 22

Describe signal transduction in hair cells

Answer 22

The longest specialised stereostilia is the kinocilum.

Fibrous connections called tip links pull open mechanically gated ion channels

Mechanical deformation toward the kinocilium opens K+ channels in the stereocilia.

Mechanical deformation away form the kinocilium causes the K+ channels to close

The resulting depolarisation caused by opening these mechanically gated ion channels goes on to open voltage gated Ca2+ channels and permits Ca2+ influx and neurotransmitter release.

Mechanically gated ion channels are a fast form of opening channels (compared to signal transduction in the vision etc.

Question 23

Where is pitch (frequency) determined?

Answer 23

Discrimination is determined by activity in hair cells at specific points on the basilar membrane

Question 24

Where is the intenisty (loudness) encoded?

Answer 24

Encoded in the number of impulses per second in auditory nerve fibres

Question 25

Where is duration of sound signalled?

Answer 25

Duration of the sound is signalled by duration of afferent discharge caused by the stimulus

Question 26

How is the direction of the sound source detected?

Answer 26

Direction of the sound source is indicated by time difference in activation or receptors in each ear,, and by intensity differences in each ear.

Question 27

Where are the central pathways of hearing?

Answer 27

1. Auditory receptors in cochlear
2. Brain stem neurons
3. Medial Geniculate Nucleus
4. Auditory cortex (each side receives info from both ears)

Question 28

What is deafness?

Answer 28

Raised threshold to sound stimuli

Question 29

What are two causes of deafness

Answer 29

Impaired sound transmission through outer or middle ear (conduction deafness). Can be due to blockage or infection

Damage to receptors or neural pathways (sensorineural deafness). Can be due to exposure to loud noises, some antibiotics, menigitis etc

Question 30

What can be a result of prolonged exposure to loudnesss?

Answer 30

Hair cells of the organ of corti can get damaged. Once they are damaged, they are damaged forever and cannot be healed