Chapter 11: Auditory (midterm)

Question 1

Hat are the 3 sections of the ear? Describe them

Answer 1

Outer ear: pinna conducts sounds into the auditory canal towards the tympanic membrane

Middle ear: tympanic membrane, ossicles (malleus, incus, stapes)

Inner ear: cochlea-fluid filled

Question 2

What are the five steps of sound transduction

Answer 2

• sound waves move tympanic membrane
• timpani c membrane moves ossicles
• ossicles move membrane at oval window
• motion at oval window moves fluid in cochlea
• movement of fluid in cochlea causes response in sensory neurons

Question 3

What are the two mechanisms that allow to overcome energy mismatch between air and water?

Answer 3

1) Lever arm ratio:
A. Ossicles act as levers
B. Malleus arm is shorter than incus arm
C. Small movements in malleus—> large movements in incus

2) area ratio:
A. Amplification due to the larger area of the tympanic membrane compared to the oval window
B. Pressure=force/area

Question 4

What are the three scalae of the cochlea?

Answer 4

Scala vestibuli
Scala media
Scala tympani

Question 5

What are the two liquids in the cochlea? Each composition?

Answer 5

Perilymph: in Scala vestibuli and tympani—> low K high Na+

Endolymp: Scala media—>high K low Na+

Question 6

Where is sound transduction accomplished?

Answer 6

Organ of Corti

Question 7

What is the word for place code on the basilar membrane?

Answer 7

Tonotopy

Question 8

How many rows of outer cells are there?

Answer 8

3

Question 9

How many rows of inner cells are there

Answer 9

1

Question 10

What causes deflection of Stereocilia in hair cells?

Answer 10

Movement of basilar membrane

Question 11

Which movement of Stereocilia depolarized the hair cell?

Answer 11

Toward kinocillium

Question 12

Which movement of Stereocilia hyperpolarizes hair cell?

Answer 12

Away from kinocillium

Question 13

What is the resting membrane potential of the hair cell?

Answer 13

-70mV

Question 14

What does depolarization in hair cell cause?

Answer 14

Opens voltage gated Ca++ channels. The presence of Ca++ causes release of neurotransmitter
This release causes depolarization of 8th nerve afferent

Question 15

What is the cochlear amplifier? What is the effect on the basilar membrane?

Answer 15

As the cell membrane potential fluctuates up and down, molecules called prestin expand and contract.
As a result, the cell membrane will expand and contract.

This makes the basilar membrane move, amplifying it’s movements

Question 16

What are the six steps of the auditory pathway?

Answer 16

Spiral ganglion—>ventral cochlear nucleus—>superior olive—>inferior colliculus—>Medial Geniculate Nucleus—>auditory cortex

Question 17

What must the auditory system encode?

Answer 17

Frequency of sound
Intensity of sound
Location of sound

Question 18

What are the two mechanisms for intensity coding?

Answer 18

1. Increase in firing rates: high intensity sound will cause a higher firing rate than a low intensity sound for the same frequency
2. As a consequence of more intense stimuli, the basilar membrane mover over a greater distance, increasing the number of active hair cells

Question 19

What is the most fundamental way of representing frequency in the auditory system? What is it?

Answer 19

Tonotopic organization

There is a corresponding tonotopic representation in the auditory nerve. Auditory nerve fibers connected to hair cells near the apical basilar membrane have low characteristic frequencies and those connected to hair cells near the basal basilar membrane have high characteristic frequencies.

Question 20

What is another mechanism for frequency coding (not tonotopy)

Answer 20

Phase locking or “volley principle”:

Front of AP at the same spot of the sound wave. Not always on each one!

Question 21

What is the limit frequency for phase locking?

Answer 21

4kHz

Question 22

What are the two mechanisms of sound localization? What are their characteristic frequencies?

Answer 22

• interaural timing differences (btw 20-2000Hz)

- interaural intensity differences ( btw 2000-20000Hz)

Question 23

What are binaural neurons in the medial superior olive tuned to?

Answer 23

Different interaural time delays: EE cells

Question 24

What are binaural neurons in the lateral superior olive tuned to?

Answer 24

Different interaural intensity differences - EI cells

Question 25

Explain how the interaural intensity difference works

Answer 25

(Sound coming from left ear)

1) stronger stimulus to left ear excited left LSO
2) this stimulus also inhibits right LSO via trapezoid body
3) excitation from left side is greater than inhibition from right side, resulting in net excitation on left side
4) inhibition from left side is greater than excitation in right side, resulting in net inhibition on the right side

Question 26

What is the columnar organization of the auditory cortex?

Answer 26

• isofrequency bands: analysis of sound frequency

- binaural bands: analysis of sound location

Question 27

Describe the ways in which the receptive fields of cells in lay 4C in primary visual cortex are different from the cells located in laminae above and below them.

Answer 27

4C cells are monocular, have center-surround organization
Above and below cells can be binocular, have simple or complex receptive fields, which are orientation selective, and can be direction selective

Question 28

What effect would the following changes have on the amplitude of inner hair cell membrane potential depolarization in response to incoming sounds: “Increased K+ concentration in the endolymph”

Answer 28

Higher peak amplitude: Stronger concentration gradient leading to more K+ influx

Question 29

Explain how low, medium, and high frequencies are coded for in the auditory system.

Answer 29

LOW: Frequency Coding and phase locking
Low range frequencies are coded through the firing of action potentials for auditory axons. There is less specificity when looking at just the basilar membrane for lower frequencies, so the rate of firing of Aps help to determine them. Frequency Coding and
MEDIUML: Volley principle and Tonotopy
Medium range frequencies are coded with both detection on the basilar membrane as well as the depolarization across multiple auditory axons.
HIGH: Tonotopy / Place Coding
High frequencies are coded with the basilar membrane. It isn’t feasible to keep up with the frequency with just action potentials, so the base of the basilar membrane (where the detection for higher frequencies on the tonotopic map is) has more accuracy

Question 30

What is the consequence of Inactivating mutation in the outer hair cell motor protein prestin (needed for contraction):

Answer 30

All sounds seem quieter (because outer hair cells cannot contract without their motor protein)

Question 31

What is the consequence of Damage to the left auditory nerve (cranial nerve VIII

Answer 31

Loose hearing in one ear, harder to localize sounds, particularly in the horizontal plane

Question 32

There are three sources of amplification of the incoming signal in the ear. (Hint: Two in the middle ear and one in the inner ear)

Answer 32

Ossicles amplify the vibration that comes in from the tympanic membrane by two impedence matching mechanisms: lever arm ratio and the area ratio; the outer hair cells also work to amplify the vibration of the basilar membrane because of the motor protein, prestin in the cell membrane