Exam 3 Week 14 ppt 9 Auditory Pathways

Question 1

Where do cell bodies of the primary afferent bipolar neurons reside

Answer 1

in spiral ganglion

Question 2

Where do axons of bipolar neurons enter brain stem?

Answer 2

lateral and slightly caudal to vestibular 1° afferents

Question 3

Where do axons of bipolar neurons end?

Answer 3

on dorsal and ventral cochlear nuclei

Question 4

How are cochlear relay nuclei tonotopically mapped?

Answer 4

high frequencies dorsal and low frequencies ventral

Question 5

What are the Cochlear Nuclei in the ascending pathway?

Answer 5

the 2° or relay auditory neurons

Question 6

What path do axons of cochlear nuclei take?

Answer 6

Axons take 1 of 3 paths:

1. Ventral acoustic stria (trapezoid body) – running ventrally thru caudal pontine tegmentum
2. Dorsal and intermediate acoustic stria (running more dorsally through caudal pons)
3. Most ascend contralaterally as lateral lemniscus

• Some ascend in ipsilateral lateral lemniscus
• Some synapse on a variety of nuclei in pons – most prominent is superior olivary nucleus
• NOTICE BILATERAL PATH

Question 7

True or false: Lateral lemniscus have only axons from 2° auditory neurons

Answer 7

False

Lateral lemniscus have both Axons from 2° auditory neurons and few 3° from superior olivary nucleus

Question 8

How does lateral lemniscus ascend?

Answer 8

• Ascends lateral to spinothalamic tract

- A few synapse in nucleus of lateral lemniscus but most ascend to inferior colliculus

Question 9

Inferior Colliculi in Ascending Pathway- 3 points to know

Answer 9

1. Most 2° auditory neurons end on neurons in inferior colliculus (a few ascend to the thalamus)
2. Axons from these 3° neurons ascend to thalamus as brachium of inf colliculus
3. Tonotopic mapping with high frequencies more ventral and low more dorsal

Question 10

Medial Geniculate Nucleus in Ascending Pathway- 3 points to know

Answer 10

1. 3° axons end on 4° in medial geniculate nucleus of thalamus
2. Axons give rise to auditory radiations to 1° auditory cortex
3. Tonotopic mapping with high frequencies medial and low frequencies lateral

Question 11

What makes up the Primary Auditory cortex?

Answer 11

Transverse temporal gyrus (1) and adjacent planum temporale (2)

Question 12

Which side of brain has a larger representation of the primary auditory cortex

Answer 12

left

Question 13

Tonotopic mapping of Primary Auditory cortex

Answer 13

low frequencies anterior and high frequencies more posterior

Question 14

Where do 2° axons from cochlear nuclei decussate?

Answer 14

in 1 of 3 locations
1. Axons of superior olivary nucleus also decussate in the trapezoid body (inferior acoustic stria)
2, Commissural connections between the inferior colliculi
3. ? did not see anything clearly marked

Question 15

Bilaterality of acoustic projections

Answer 15

means that loss of one central pathway or loss of auditory cortex does not produce deafness in one ear but issues related to sound localization and indentification
**Due to: axons that have already decussated may decussated again

Question 16

What two peripheral mechanisms contribute to the ability to localize sounds?

Answer 16

• Difference in timing between sound arriving at one ear versus the other (interaural time difference - ITD)
• Difference in sound intensity between the two ears (interaural intensity difference - IID)

Question 17

What is time difference best at?

Answer 17

determining the direction of low frequencies

Question 18

What is intensity difference best at?

Answer 18

distinguishing the direction of high frequencies

Question 19

What is head a great sound barrier for?

Answer 19

high frequencies

Question 20

What does Pinnae of the ear do?

Answer 20

assists in sounds to the front, back and above which would not be distinguishable

Question 21

What is Lateral superior olive specialized for?

Answer 21

high frequencies and cells measure IIDs by integrating ipsilateral excitatory and contralateral inhibitory inputs

Question 22

What is Medial superior olive is specialized for?

Answer 22

low frequencies and measures ITDs using excitatory inputs from both sides

Question 23

example of auditory reflexes

Answer 23

the tensor tympani/stapedius reflex

Question 24

Afferent (sensory) limb of tympani/stapedius reflex

Answer 24

A few fibers from the auditory nuclei terminate in the nuclei of the facial and trigeminal motor nuclei

Question 25

Efferent (motor) limb of tympani/stapedius reflex

Answer 25

Branch of facial nerve to stapedius

Branch of trigeminal nerve to tensor tympani

Question 26

Function of tensor tympani/stapedius reflex

Answer 26

to limit amplitude of loud and high-frequency sounds and to filter out noise arising from the head itself

Question 27

Name the major structures auditory pathways travel through, and indicate where decussation may occur. (7 structures, 2 levels of decussation)

Answer 27

1. Cochlear Nuclei (Ventral and dorsal)
   (decussation may occur in ventral, intermediate, or dorsal acoustic stria - ventral acoustic stria = trapezoid body)
2. Superior olivary nucleus (not all fibers go through this)
3. Lateral lemniscus (tract and nucleus)
4. Inferior Colliculi (nuclei)
   (may deccusate here between the two inf. colliculi)
5. Brachium of inferior colliculus (tract)
6. Medial Geniculate Nucleus (part of thalamus)
7. Primary Auditory Cortex

Question 28

Describe the tonotopic orientation of high frequency signals as they travel through the auditory pathway:

Answer 28

1. Cochlear nuclei: dorsal
2. Inferior colliculus: ventral
3. Medial Geniculate Nucleus: medial
4. Primary Auditory Cortex: posterior

Question 29

Describe the tonotopic orientation of low frequency signals as they travel through the auditory pathway:

Answer 29

1. Cochlear nuclei: ventral
2. Inferior colliculus: dorsal
3. Medial Geniculate Nucleus: lateral
4. Primary Auditory Cortex: anterior

Question 30

Name the options for decussation of the auditory pathway:

Answer 30

1. After leaving the chochlear nuclei: Trapezoid body (ventral acoustic stria) OR dorsal or intermediate acoustic stria
2. At the Inferior Colliculi