Exam 2 Hearing 2

Question 1

_________ hair cells respond to sound with both a receptor potential and a change in length.

•Motion of the cell body in response to changes in cell membrane potential may augment basilar-membrane motion, and create a cochlear amplifier.

-depolarization casues motor proteins to contact

Answer 1

Outer

Question 2

____ hair cells produce their greatest response at a characteristic sound frequency

Answer 2

Inner

Question 3

_____ hair cells are for protection and amplification of sound

Question 4

________ hair cells are for transduction and do NOT contract

Answer 4

Inner

Question 5

How is a hair cell depolarized?

Answer 5

Entry of K+ into the hair cell causes depolarization not hyperpolarization because endolymph is high in K+.

• Depolarization activates voltage-gated Ca2+ channels.
• Entry of Ca2+ triggers the release of neurotransmitter.

–Neurotransmitter activates spiral ganglion fibers.

Question 6

Explain the auditory pathway

Answer 6

• Afferents from the spiral ganglion enter the brainstem in the auditory nerve.
• At the level of the medulla, the axons innervate the dorsal and ventral cochlear nuclei ipsilateral to the cochlea where the axons originated.

–Sound processing begins in the cochlear nuclei.

• There are multiple pathways from here on.
• All ascending auditory pathways converge onto the inferior colliculus.
• The MGN is in the thalamus.
• There is extensive feedback in the auditory pathways.
• Other than the cochlear nuclei, auditory nuclei in the brain stem receive input from both ears.

Question 7

What is the systematic organization within an auditory structure based on characteristic frequency?

-_______maps are found on the basilar membrane, auditory nerve, and cochlear nucleus.

•________ maps also are found within each of the auditory nerve relay nuclei, the medial geniculate nucleus (MGN) and the auditory cortex.

Answer 7

Tonotopy

Question 9

Explain the basic mechanisms for coding pitch

Answer 9

• Pitch gets encoded in the cochlea by hair cells, each of which has a best frequency.
• Each of these hair cells measures the energy in a narrow band of frequencies and encodes this measure in the nerve discharge.
• The array of hair cells provides the central nervous system (CNS) with moment-by-moment information about the frequency content of incoming sound.
• The vibration pattern of the basilar membrane along with a tonotopic arrangement of hair cells along the membrane helps to sharpen the response of the hair cells.
• Overall, this arrangement provides the CNS with the frequency spectrum of the sound signaled via approximately 30,000 nerve fibers per cochlea.

Question 10

WHat are the two interrelated ways that sound intensity is coded?

Answer 10

Rate

Recruitment

Question 11

How does rate code for sound intensity?

Answer 11

As sound intensity increases, the discharge rate of individual hair cells increases.

Question 12

How does recruitment code for sound intensity?

Answer 12

•As sound intensity increases, additional receptors get recruited. Not all receptors have the same threshold.

Question 13

–An auditory neuron is most responsive to sound at one frequency, called its ________ frequency, and it is less responsive at neighboring frequencies.

-it will only fire when it gets this frequency

Answer 13

characteristic

Question 14

The louder the sound, the _____ an auditory nerve fiber fires action potentials.

Answer 14

Faster

Question 15

Louder sounds produce movements of the basilar membrane over a greater distance. Thus, ____ neurons are activated as sound intensity increases.

Answer 15

More

Question 16

•The main source of information about sound frequency that complements information derived from tonotopic maps is the timing of neural firing, which is called?

Answer 16

Phase locking

Question 17

•How different sound frequencies are represented.

–At very ______ frequencies, phase locking is used

–At ________ frequencies, phase locking and tonotopy are used.

–At _____ frequencies, tonotopy is used.

Answer 17

1) Low
2) intermediate
3) high

Question 18

Localization of sound in the horizontal plane occurs because of the ______

Answer 18

duplex theory of sound localization

Question 19

____________ is the time difference between the sound arriving at one ear and then the other ear.

-This provides a cue to the location of sound.

Answer 19

Interaural time delay

(a) Sound waves coming from the right side will reach the right ear first, and there will be a large interaural delay before the sound propagates to the left ear.
(b) If the sound comes from straight ahead, there is no interaural delay. Delays for three different sound directions are shown.

Question 20

_________does NOT help to localize sound when a continuous sound is emitted.

The sound is always present in both ears and there is no delay.

This sound is located by interaural intensity difference.

–The peak of the sound wave reaches one ear before the other.

–The head casts a sound shadow causing a more intense sound in one ear than the other.

Answer 20

•Interaural time delay

Question 22

________ are sensitive to sound localization.

Answer 22

•Binaural neurons

Question 23

Explain this image

Answer 23

•Binaural neurons are sensitive to sound localization.

–The figure shows delay lines and neuronal sensitivity to interaural delay.

Question 24

•Localization of sound in the vertical plane is based on reflection from the _______.

Answer 24

pinna