PSC1002/L23 Hearing & the Ear

Question 1

Define sound.

Answer 1

Longitudinal pressure wave travelling through air or other medium

Question 2

How is sound defined? (2)

Answer 2

Frequency (tone)
Amplitude (intensity)

Question 3

Describe the composition of a pressure wave.

Answer 3

Alternate compression and rarefaction of molecules

Question 4

Give the 3 ossicle bones.

Answer 4

Malleus
Incus
Stapes

Question 5

How does the pinna allow gathering of sound in some species?

Answer 5

Orientates towards source

Question 6

What is the role of the eustachian tube?

Answer 6

Opens/closes to equalise pressure

Question 7

How does the area of the tympanic membrane compare to the the stapes? Why?

Answer 7

Area of tympanic membrane greater than footplate of stapes
Increases pressure

Question 8

How large is an uncoiled cochlea?

Answer 8

2mm diameter
35mm long

Question 9

Give the 3 chambers of the cochlea.

Answer 9

Scala vestibuli
Scala media
Scala tympani

Question 10

How many rows of inner hair cells do human ears have?

Answer 10

1 row = 3,500

Question 11

How many rows of outer hair cells do human ears have?

Answer 11

3 rows = 12,000

Question 12

What are the small processes at the tips of hair cells?

Answer 12

Stereocilia

Question 13

What is the role of stereocilia? (2)

Answer 13

Bend in response to pressure changes
Of tallest row of outer hair cells, embedded in tectorial membrane

Question 14

Describe what occurs when sound enters the cochlea with regards to frequency analysis. (6)

Answer 14

Basilar membrane vibrates
Travelling waves travel up basilar membrane from base to apex
Position of maximal displacement depends on frequency of sound
Low frequencies produce maximal displacement at apex of cochlea
High frequencies produce maximal displacement at base
Displacement of basilar membrane excites hair cells

Question 15

What does excitation of inner hair cells lead to? (2)

Answer 15

Transmitter release
Excitation of auditory nerve fibres

Question 16

What occurs when stereocilia bend towards longest? (4)

Answer 16

Entry of K+ leads to depolarisation
Ca2+ entry
Transmitter release
Transmitter activates nerve fibres

Question 17

What occurs when stereocilia bend towards shortest? (4)

Answer 17

No K+ entry
Hyperpolarisation
No transmitter
Nerves stop firing

Question 18

What causes bending of stereocilia? (2)

Answer 18

Movement of basilar membrane
Interaction with tectorial membrane

Question 19

Which 2 ways can cochlea filter by frequency?

Answer 19

Each neuron responds best to one frequency
Each location along cochlea amplifies one frequency

Question 20

What kind of drugs can harm outer hair cells?

Answer 20

Ototoxic drugs

Question 21

What happens to outer hair cells as stereocilia bend and sound stimulation?

Answer 21

Change length

Question 22

What are outer hair cells driven by?

Answer 22

Prestin
Motor protein in OHC membrane

Question 23

What does the lengthening and shortening of outer hair cells do?

Answer 23

Inject energy
Amplify basilar membrane movement