23. Biophysics of hearing: roles of outer and middle ear in transferring sound into the inner ear. Deformations of basal membrane as a function of frequency. Signal generation by hair cells.

Question 1

Define the human hearing range (thereshold of hearing, threshold of pain, frequency limits).

Answer 1

Threshold of hearing is the minimum intensity at various frequencies that a human can hear. The threshold for pain is the highest intensity that a human can hear for a short time without damage to the ear (10 W/m^2). The frequency range is between 20Hz-20kHz.

Question 2

Does a greater dB value always correspond to a louder sound?

Answer 2

Only if the frequency is the same

Question 3

Does a greater phon value always correspond to a louder sound?

Answer 3

Yes

Question 4

Does a greater sone value always correspond to a louder sound?

Answer 4

Yes

Question 5

The role of outer ear in transferring sound into the inner ear

Answer 5

Made of the auricula, external auditory canal and eardrum
→ The auricula steers the sound waves towards the external auditory canal, which then transmits the sound towards the eardrum.

→ The eardrum is brought into resonance by the sound wave and will transmit the vibrations towards the middle ear.

Question 6

The role of middle ear in transferring sound into the inner ear

Answer 6

The middle ear transmit vibrations of tympanic membrane to oval window, a smaller membrane of inner ear

Question 7

The outer and middle ears are filled with (1)__

The inner ear is filled with (2)___

Answer 7

1. air
2. water

Question 8

Why does sound move from outer ear to inner ear is almost completely reflected?

Answer 8

Because of large difference in acoustic impedance at air-water boundary

→ Z of inner ear is larger than that of outer ear

(outer and middle ears are filled with air

inner ear is filled with liquid)

Question 9

Describe the mechanical oscillating system of middle ear

Answer 9

The mass of ossicles, elasticity and internal friction of suspended muscles form a mechanical oscillating system

→ Delimits frequency of the highest pitch entering the inner ear which is about 20k Hz

Question 10

Describe the basilar membrane

Answer 10

The membrane that divide the cochlea into 2 parts

Question 11

Describe the organ of Corti

Answer 11

The organ that lies above the basilar membrane → contains thousand of hair cells and nerve endings

Question 12

What does the theory dissed by George Bekesy state?

Answer 12

Surface waves travel along the basilar membrane when stimulated by sound

Question 13

How can basilar membrane indirectly generate electric potentials?

Answer 13

Vibrations of basilar membrane bend the hair cells of the organ of Corti → generate electric potential

Question 14

What are the hair cells?

Answer 14

They are signal transducers of hearing which can be found in the Organ of Corti resting on basilar membrane

Question 15

What are the 2 categories of hair cells?

Answer 15

According to position, there are inner and outer hair cells

Question 16

The role of hair cells in the processing of hearing

Answer 16

Traveling waves flex the basilar membrane

→ the tectorial membrane (overlays the ahi cells) shifts relative to hair cells to generate a mechanical shear force in the plums of hair cell

• Inner cells act as mechanoelectric transducers

→ Sound stimulus cause the plums to lean which generates a change in electrical potential of hair cells’ membrane

→ This change is a depolarizing nature → means a frequency increase of the action potential

Question 17

The role of inner hair cells in the processing of hearing

Answer 17

Inner cells act as mechanoelectric transducers

→ Sound stimulus cause the plums to lean which generates a change in electrical potential of hair cells’ membrane

→ This change is a depolarizing nature → means a frequency increase of the action potential

Question 18

The role of outer hair cells in the processing of hearing

Answer 18

Its role is the active mechanical amplification of sounds of weak and moderate intensity by the consumption of biological energy

→ outer hair cells sense vibrations of the basilar membrane

→ results in changes to length of hair cells according to the sound

→ outer hair cells act as an amplifier with positive feedback

Question 19

How is vibration related to frequency?

Answer 19

The number of vibrations per second is known as the frequency

Question 20

Vibrations amplified by the outer hair cells are sensed by __

Answer 20

Inner hair cells

Question 21

The role of Bekesy’s traveling waves of basilar membrane

Answer 21

Bekesy’s traveling waves of basilar membrane contribute passively (without consuming external energy) to preselection of sound frequencies

Question 22

3 benefits of having outer hair cell as an active biomechanics motor and amplifier with positive feedback render

Answer 22

• Sharp fre