Efferent Pathways

Question 1

carrying something away from a central organ or part

Answer 1

efferent

Question 2

what does efferent refer to in the CNS

Answer 2

refers to neurons carrying impulses away from the CNS which means away from the brain, or brainstem or spinal cord

Question 3

There are ______ connects to both the auditory and vestibular peripheral sensory organs

Answer 3

efferent

Question 4

what is an efferent connection in the middle ear?

Answer 4

Efferent motor control over the stapedius and tensor tympani muscles

Question 5

What are the efferent pathways called?

Answer 5

descending auditory pathways
centrifugal pathways

Question 6

what are the two sections of the efferent pathway?

Answer 6

rostral - descending fibers from the cortex to the lower auditory centers
caudal - aka olivocochlear bundle/Rasmussen’s bundle, from the superior olivary complex out to the cochlea

Question 7

what are the divisions of the OCB?

Answer 7

crossed olivocochlear bundle (COCB
uncrossed (UCOCB)

Question 8

A1 is rostral to the superior olivary complex.

Answer 8

true

Question 9

Where does the rostral division of efferent pathway originate and descend?

Answer 9

originates in Auditory cortex
descends to mgb and IC (fibers here may give rise to other efferent fibers)

Question 10

what do the centrifugal pathways allow

Answer 10

higher auditory system areas like the auditory cortex to modify the activity, sensory processing and focus attention on stimuli at lower levels

Question 11

how many efferent neurons are in the OCB (caudal efferent system)

Answer 11

about 1600

Question 12

besides the crossed and uncrossed classification of caudal efferent system, how else are they categorized

Answer 12

by where in the superior olivary complex the fibers arise. The lateral tract fibers originate from the cells near the lateral superior olive and will be referred to as the Lateral OCB and the medial tract fibers originate from cells in near the medial superior olive and will be referred to as the medial OCB

Question 13

uncrossed fibers from LSO that terminate on the dendrites underneath the IHCs

Answer 13

Lateral OCB

Question 14

fibers that are mainly crossed going directly to the contralateral OHCs

Answer 14

Medial OCB

Question 15

What do efferent fibers do?

Answer 15

bringing action potential from cortex
they control and modulate what organ of corti is doing

Question 16

Where do OCBs (efferent fibers) project

Answer 16

to the cochlea through the internal auditory canal as part of the VESTIBULAR NERVE

Question 17

What fibers attach to the OHC?

Answer 17

type II afferent
MOC efferent

Question 18

what fibers attach directly and indirectly to IHC

Answer 18

Type 1 afferent
LOC efferent attaches to afferent fiber

Question 19

What role do MOC fibers mainly play?

Answer 19

inhibitory role by suppressing the contractility of the OHCs and thus reducing the biological mechanical amplifier function played by the OHCs

Question 20

What are the functions of OCB

Answer 20

Exert control over synaptic transmission and neural signals
Mainly inhibitory role
Reduced neural output from the cochlea and auditory nerve during stimulation of the MOC (or crossed OCB –mostly MOC fibers)
However stimulation of some fibers resulted in lower thresholds for fibers in the cochlear nucleus, making them more easily stimulated (excitatory role)

Question 21

What test measures have shown the effects of the inhibitory role of the olivocochlear efferent connections

Answer 21

OAEs, tuning curves, and ABRs

Question 22

Does stimulating the OCB change tuning curves?

Answer 22

yes
The result is that the TC in not as sensitive at the characteristic frequency shown by the pointy time (see the small image as an example), and the TC may be less sharp during OCB stimulation (specifically medial OCB stimulation).

Question 23

What helps ot hear in noise?

Answer 23

MOC bundle can trigger outer hair cell motility. The changes can enhance or dampen the basilar membrane movement, with effects on how the auditory system handles the presence of masking noise. When recording ABR wave I, in the presence of noise which would trigger the efferent pathways it was found that the best condition was with ipsi and contra noise. The studies suggest that the OCB may function to assist with hearing in noise.

Question 24

what do OAEs test for?

Answer 24

outer hair cells movement

Question 25

What happens when contralateral noise is introduced during the measure of OAEs

Answer 25

the amplitude of the OAEs decreases, subtly but consistently
The noise in the contralateral ear, triggers the COCB and the efferent signals influence the OHC motility, thus changing the OAE.

Question 26

what is the main neurotransmitter of the efferent auditory system?

Answer 26

acetylcholine (gaba is also present but not the main)

Question 27

VOR

Answer 27

Vestibular system sending efferent signals to control the eye muscles

Question 28

VSR

Answer 28

signals to control muscles of the body, especially the antigravity muscles

Question 29

What are the efferent vestibular connections

Answer 29

Efferent projections to the hair cells
Originating in the reticular formation, lateral to abducens nucleus
Projecting bilaterally in the vestibular division of CN VIII
Terminating directly or indirectly (afferent nerve endings) on vestibular hair cells
Theory—compensation (modulation) for self-generated head movements vs other, but this may not be true in humans
Role unknown

Question 30

why do we have modulation?

Answer 30

hearing in noise
system gets overwhelmed and sharpens things and reduces that background noise (modulates)
does so by enhancing or dampening the basilar membrane movement

Question 31

what is the efferent auditory system NT?

Answer 31

acetylcholine