4 - Hearing & How We Do It

Question 1

below what level is hearing damage negligable?

Answer 1

75db

Question 2

what happens to the ability of a person to hear diff frequencies as they age?

Answer 2

ability to hear higher freqencies decreases

Question 3

how are ears adapted to hearing + perceiving sounds from different directions?

Answer 3

• two ears - is sound left or right? hits one ear before it hits the other.
• shape of ears - is sound from in front or behind? sound bounces and deflects.

Question 4

how do the ears “self-clean”?

Answer 4

the skin of the eardrum migrates outwards and grows out of the ear canal - it doesn’t just shed (this would clog the ear)

Question 5

at what rate does skin grow out of the ear canal?

Answer 5

0.7mm a day

Question 6

name the two different types of ear wax. what is the difference between the two?

Answer 6

• honey wax - “sticky wax” only found in african or caucasian populations
• flaky wax - only found in asian populations

Question 7

what is the role of earwax?

Answer 7

waterproofing
* stops water getting into ear and clogging ear

Question 8

what part of the ear is a human adaption to hearing sound in air instead of water?

Answer 8

the middle ear - amplifies the sound waves in air

Question 9

how is the middle ear ventilated:
* at atmospheric pressure?
* at abnormal pressure?

Answer 9

• atm - physiological gas exchange across mucosa - middle ear gas is dissolved out into mixed venous blood
• abnormal - eustachian tube opens for acute changes - “popping” ear to level pressure

Question 10

what type of vibration is air?
what type of vibration is cochlear fluid?

Answer 10

air - low pressure high-displacement
cochlear fluids - high-pressure low-displacement

Question 11

what is the ratio of the tympanic membrane:oval window?

Answer 11

20:1

Question 12

what is the function of the middle ear muscles?

Answer 12

pull ossicles and protects your hearing

Question 13

how many times does the cochlea turn?

Answer 13

2.5 times

Question 14

what is the purpose of the round window?

Answer 14

allows sound to dissipate out of the cochlear after it has hit the apex - prevents echoing of sound

Question 15

what is the function of inner hair cells?

Answer 15

transmit information to the brain

Question 16

what is the function of outer hair cells?

Answer 16

cochlear amplifier that refines the sensitivity and frequency selectivity of the mechanical vibrations of the cochlea

Question 17

where do the inner hair cells sit?

Answer 17

within the fluid

Question 18

where do the outer hair cells sit?

Answer 18

they are embedded in the tectorial membrane and so stiffen the basilar membrane so it only vibrates in one frequency

Question 19

what happens to the hair cells as a person ages?

Answer 19

outer hair cells die off - causes deafness

Question 20

what is meant by cochlear microphonics?

Answer 20

the ear fine tunes itself to hear certain frequencies

Question 21

when is cochlear microphonics lost?

Answer 21

when OHCs are poisoned

Question 22

Label the cochlea

Answer 22

Question 23

Label the cochlea

Answer 23

Question 24

what fluid does the scala media contain?

Answer 24

endolymph - high in K+

Question 25

what fluid does the scala vestibuli contain?

Answer 25

perilymph - high in Na+