Module D-12

Question 1

What are the Brodmann’s areas for primary auditory cortex?

Answer 1

Areas 41 and 42

Question 2

Which area of temporal lobe makes up primary auditory cortex?

Answer 2

the transverse temporal gyrus of Heschl on the superior surface of the temporal lobe

Question 3

The organization of the primary auditory cortex is _______

Answer 3

tonotopic

Question 4

What does the tonotopic map show?

Answer 4

the sound frequencies are mapped and distributed along a rostro-caudal axis

Question 5

Where are low freq sounds represented?

Answer 5

rostrally and laterally

Question 6

Where are high freq sounds represented?

Answer 6

caudally and medially

Question 7

How is the columnar organization of cells in the primary auditory cortex

Answer 7

• Perpendicular to the tonotopic map
• there are columns with characteristic types of binaural innervation.
• grouped according to their pattern of input from both ears.
• Cells in one set of columns are excited by input from both ears (summation columns), labeled “EE”
• Cells in the alternating columns are excited by input from one ear and inhibited by input from the other ear (suppression columns), which is labeled as “EI”

Question 8

In which layer does the input from the thalamocortical fibers come in?

Answer 8

Layer 4

Question 9

What is the Place code of Frequency?

Answer 9

the place (or location) of a nerve cell encodes for a specific
stimulus feature (frequency, in this instance)

Question 10

How are various frequencies distinguished?

Answer 10

Near the oval window, at its base, the basilar membrane is narrow and stiff, and therefore is activated most effectively deflected by high frequencies.
At the tip (apex) of the cochlea (helicotrema), the basilar membrane is wide and floppy, and therefore most effectively deflected by low frequencies.
The varied deflection causes varied activation of hair cells specific to the frequency of the sound

Question 11

Which waves travel further in the cochlea?

Answer 11

Low frequency waves

Question 12

What is Frequency code?

Answer 12

the frequency of action potentials in afferent fibers
increases with sound intensity
encoding method for stimulus intensity

Question 13

What is Volley code?

Answer 13

Encoding method for sound intensity that based on number of afferent fibers activated
low intensity sound only activates low threshold fibers. Higher sound intensities result in the recruitment of additional afferent fibers with higher
thresholds.

Question 14

How many auditory nerve fibers does each hair cell synapse with?

Answer 14

20

Question 15

How is low frequency sound localized?

Answer 15

• interaural time differences.
• the first pressure wave arrives at different times at the
  different ears.

Question 16

what pathway is used to detect the time delay for low freq sound localization?

Answer 16

the binaural pathways to the superior olive (MSO)
by a mechanism called “coincidence detection”
EPSPs produced in a neuron of the superior olive at the same time (coincidence) by signals arriving
from both ears will produce a larger signal in this neuron than EPSPs arriving at different times (no coincidence)

Question 17

How is high frequency sound localized?

Answer 17

the differences in sound intensity in the two ears when the sound originates from positions lateral to the midline
, the ear on the side opposite to the sound source is in the
acoustic shadow produced by the head ( a diminished
sound pressure signal with
a lower intensity (amplitude)

Question 18

what pathway is used to detect the time delay for high freq sound localization?

Answer 18

1) Fibers carrying auditory information synapse in the
ipsilateral superior olive, where they form excitatory
synapses.
2) collaterals from these fibers cross the midline of the brainstem and form excitatory synapses on inhibitory interneurons in the contralateral trapezoid nucleus.
3) Neurons in the trapezoid nuclei send their axons to the superior olive on the same side, where they form inhibitory synapses.
4) The neurons in the superior olive receive direct excitatory input from the ipsilateral sensory input fibers, and indirect inhibitory input via interneurons in the
trapezoid nucleus, which had received excitatory input from the contralateral sensory input fibers.
5) excitation (depolarization) in one superior olive, which is forwarded to higher regions in the brainstem and cortex. The superior olive on the other side will be inhibited (hyperpolarized) and produce no output signals.

Question 19

Localization of sound is performed in the _________ of the brainstem

Answer 19

superior olive

Question 20

The medial part of the superior olive uses __________ for interaural time differences, which is most effective for ___ frequency sounds

Answer 20

coincidence detection; low

Question 21

The lateral part of the superior olive uses interaural _____ differences, which is most effective for ____ frequency sounds.

Answer 21

amplitude; high

Question 22

Weber’s test for someone with _______ hearing loss in one ear, the sound lateralizes to the ipsilateral side

Answer 22

conductive

Question 23

Weber’s test with _________ hearing loss, the sound lateralizes to the contralateral side (side of normal hearing).

Answer 23

sensorineural

Question 24

When performing the Rinne’s test in normal subjects, __ conduction is better (and lasts longer) than ____ conduction. why?

Answer 24

air; bone

Because in air the sound waves can be amplified by the middle ear (size difference)

Question 25

When performing the Rinne’s test in patients suffering from _________ hearing loss there is decreased sound
perception during ___ conduction than _____

Answer 25

conductive; air;bone