CNS/Sensory VI

Question 1

What is sound?

Answer 1

Pressure waves moving past your head.

Question 2

What does the amplitude of a sound wave correspond to?

Answer 2

Its loudness.

Question 3

What does the frequency of sound correspond to?

Answer 3

The number of cycles per second, which indicates pitch.

Question 4

What is the normal audibility curve?

Answer 4

It depicts the relationship between how you perceive sound and the frequency of the sound waves (pitch) + the loudness of the sound (amplitude).

Question 5

What is the formula for a dB?

Answer 5

dB = 20 log (sound pressure / reference pressure)

Question 6

Going from 20 dB to 60 dB means that the sound amplitude has gotten […] times larger. Explain why.

Answer 6

100 X, since every 20 dB equals 10 X more.

Question 7

How does the damage threshold differ from the pain threshold?

Answer 7

The pain threshold exists above the damage threshold, meaning that you can damage your hearing without necessarily feeling pain.

Question 8

What frequency range do humans hear best?

Answer 8

100 to 10,000 Hz

Question 9

What is the damage threshold for audibility?

Answer 9

Around 85 dB

Question 10

What is the pain threshold for audibility?

Answer 10

At low frequencies, around 160 dB and within our typical audible range, around 130-140 dB.

Question 11

Why is presbycusis?

Answer 11

It is the gradual loss of the ability to hear high frequency sounds will age.

Question 12

Describe the major parts of the ear from outside to inside.

Answer 12

Pinna, external auditory canal, tympanic membrane, middle ear (malleus incus and stapes connected to eustachian tube), inner ear (cochlea).

Question 13

What is the function of the pinna?

Answer 13

It is shaped in order to reflect sound into the ear canal.

Question 14

What is the function of the eustachian tube?

Answer 14

It connects the middle ear to the throat.

Question 15

What is the function of the cochlea?

Answer 15

It is where transduction occurs.

Question 16

Where are the semicircular canals located and what is their function?

Answer 16

They are located in the inner ear. Their function is to encode angular acceleration of the head.

Question 17

What is the oval window?

Answer 17

It serves as an input to the cochlea.

Question 18

Where are the sensory epithelia located and what is their function?

Answer 18

They are located in the inner ear as part of the cochlea. They are where neurons are located and where the transduction of ion channels occurs.

Question 19

Where are the utricle and saccule located and what is their function?

Answer 19

They are located in the inner ear as part of the cochlea. They encode vertical and horizontal acceleration.

Question 20

Describe the trajectory of sound up to its arrival in the inner ear.

Answer 20

Sound energy will push and pull the tympanic membrane. The membrane is connected to the malleus, incus, and stapes, which are in turn attached to the oval window in the inner ear. When the typanic membrane vibrates, the bones transmit this to the oval window, allowing the energy to reach the inner ear and exert pressure on the cochlear fluid.

Question 21

What are the three bones in the middle ear and what is their function?

Answer 21

The malleus, incus, and stapes. Their function is to connect the tympanic membrane to the oval window in the inner ear, amplifying the vibrations to the small inner space. This produces a pressure force that can produce vibrations in the fluid of the cochlea in the inner ear.

Question 22

The movement of the middle ear bones is mediated by […]

Answer 22

Skeletal muscles

Question 23

How does the activity of the inner ear bones change in a very noisy environment?

Answer 23

The skeletal muscles that modulate the amplification by the inner ear bones will tense so that it takes more energy to move the oval window back and forth. This protects the auditory system.

Question 24

Where is the round window located and what is its function?

Answer 24

It is located right below the oval window at the boundary between the middle ear and the inner ear. It moves opposite to the movement of the oval window (moves out when the OW moves in and vice versa). This helps cochlear fluid move in the inner ear.

Question 25

Explain how sound energy travels once it has gotten into the inner ear.

Answer 25

The movement of the oval and round windows allows for the vibrations to travel through the cochlear fluid. The waves in the fluid cause the basilar membrane to move up and down.

Question 26

The motion of the basilar membrane is dependent on […]

Answer 26

Frequency

Question 27

What part of the basilar membrane vibrates when the sound is low frequency?

Answer 27

The outermost part relative to the middle ear.

Question 28

What part of the basilar membrane vibrates when the sound is high frequency?

Answer 28

The innermost part relative to the middle ear.

Question 29

What part of the basilar membrane vibrates when a complex sound is played?

Answer 29

Many different locations will vibrate at once.

Question 30

What is done with the motion of the basilar membrane once it vibrates? Where does this occur?

Answer 30

The motion is converted into neuronal activity at the organ of Corti.

Question 31

Describe the structure of the organ of corti and the key cells in it.

Answer 31

The basilar membrane is at the bottom. Stacked on top of it is various cells, increase outer hair cells and inner hair cells. These hair cells have stereocilia. On top of the hair cells is the tectorial membrane.

Question 32

Where are ion channels located in the ear?

Answer 32

In the hair cells.

Question 33

How many rows of each type of hair cells are there in the organ of Corti?

Answer 33

There are 3 rows of outer hair cells and 1 row of inner hair cells.

Question 34

Explain how the basilar membrane interacts with the hair cells and the effect produced.

Answer 34

As the basilar membrane moves up and down, the stereocilia of the hair cells move and get bent. This produces biomechanical forces with the tectorial membrane. This causes the stereocilia to bend one way or the other depending on how the basilar membrane is moving.

Question 35

How do the properties of outer hair cells differ from those of inner hair cells

Answer 35

Outer hair cells are capable of moving on their own, and they have electomotility. This allows them to move back and forth in response to sound.

Question 36

Outer hair cells […] when depolarized and […] when hyperpolarized.

Answer 36

Shorten, lengthen

Question 37

What is the hypothesized function of hair cell electromotility?

Answer 37

It augments basilar membrane motion.

Question 38

Give an example of how outer hair cell electromotility can be used clinically.

Answer 38

The otoacoustic emissions, meaning the reflex of the outer hair cells to move, can be used to evaluate hearing in newborns. If a click is produced, this means the auditory system is functioning correctly.