Auditory and Vestibular Pathways

Question 1

What is the afferent auditory pathway from the hair cells to the primary auditory cortex? How many neurons?

Answer 1

hair cells

thorugh aucitory nerve to cochlear nucleu

throuh trapeoid body to superior olivary complex

thoruhg lateral lemniscus to inferior colliculus

through brachium of IC to medial genicular nucleus

through internal capsule to the primary auditory cortex

6 neurons in total

Question 2

What are the three efferent outputs in the auditory pathway?

Answer 2

from the superior olivary complex to the:

1. hair cells
2. tensor tympani
3. stapedius

Question 3

Through what nerve do the efferent fibers travel to reach the hair cells? The tensor tympani? The facial motor nucleus?

Answer 3

auditory nerve to hair cells

trigminal V3 to tensor tympani

Facial nerve to stapedius

Question 4

What sort of sounds will the acoustic reflex protect the ear from?

Answer 4

it will protect the ear from loud, low frequency tones, but it won’t protect against high pitched, quick tones like gun shots - this is because it’s slow and won’t be able to activate in time to do any good

Question 5

Because there is extensive bilateral connections int he auditory system, what is the only way to have an ipsilateral hearing loss form a single lesion?

Answer 5

you’d have to have a peripheral defect, like at the cochlea, auditory nerve or cochlear nucleus (the cochlear nucleus projects bilaterally, so anything after that would affect both sides)

Question 6

Bilateral hearing loss from a single lesion has to be…

Answer 6

central

Question 7

In the vestibular pathway, the hair cells project to what nuclei thorugh what nerve?

Answer 7

it’s easy…

to the vestibular nuclei via the vestibular nerve

Question 8

How many vestibular nuclei are there?

Answer 8

4 on each side - superior, lateral, medial, and inferior

Question 9

What part of the thalamus does the vestibular nulei project to? Through wha tpathway?

Answer 9

to the vetroposterior nucleus by the medial lemniscus

Question 10

What are the three reflexes the vestibular pathway is involved in?

Answer 10

the vestibulo-occular reflex

the vestibulocerebellar reflex

the vestibulospinal reflex

Question 11

What does the vestibulospinal reflex do?

Answer 11

It runs in the lateral vestibulospinal tract and the medial vestibulospinal tract

lateral is related to limb and trunk position in comparison to the head

medial is related to upper back and neck position in comparison to the head

Question 12

What does the vestibulo-ocular reflex (VOR) do?

Answer 12

It’s what keeps your eyes focused on one thing while your head moves

Question 13

What tract does the vestibulo-ocular reflex run through on its way to the oculomotor, abducens, and trochlear nuclei?

Answer 13

the medial lontiduinal fasciculus

Question 14

What are 1 ,2 and 4

are they involved in the auditory or vestibular pathways

Answer 14

1 - medial geniculate of the thalamus

2. branchium to the inferior colliculus
3. inferiro colliculus

auditory

Question 15

Where will the median and inferior vestibular nuclei be located in relation to other landmarks in the mid medulla?

Answer 15

it will be dorsal to the solitary tract/nucleus

lateral to the 4th ventricle

Question 16

In the more rostral medulla, what nucleus will you be able to see very lateeral?

Answer 16

the cochlear nucleus

Question 17

In the caudal pons, the facial nerve divides the facial nuclei and the abducens nuclei from what other nuclei involved in the vestibular system?

Answer 17

the superior vestibular nucleus

Question 18

In the midbrain, what important auditory pathway structures are located laterally from the periaqueductal gray?

Answer 18

the inferior colliculus and brachium

Question 19

Why is the auditory pathway especially myelinated?

Answer 19

It is highly concerned with temporal acuity, so it has to be precist

it only takes 10 mS between when a sound occurs and the nerve begins to conduct

Question 20

The superior olivary nucleus is involved in the localization of sound by comparing the sound received by the two ears

more specifically, the lateral superior olive neurons localize ___ frequency stimuli by comparing interaural ___ differences

while

the medial superior olive neurons localize ___ frequency stimuli by comparing interaural ____ differences

Answer 20

lateral: compares interaural intensity differences to compare localize high frequency stimuli
medial: compares interaural timing differences to localie low frequency stimuli

Question 21

When is the function of the vestibulospinal reflexes most evident?

Answer 21

decerebrate rigidity

Question 22

How do the lateral vestibulospinal tract and medial vestibulospinal tract differ in terms of their afferent source?

Answer 22

the lateral gets afferents form the entire membranous labyrinth in the inner ear while the medial gets only from the semicircular canals

this means the lateral gets motion and gravity info while the medial gets only motion

Question 23

Specifically for function, which vestibulospinal tract is in charge of posteural changes to compensates for tilts and movement of the body and which is responsible for stabilizing head position during walking?

Answer 23

lateral

medial

Question 24

How do the efferent connections and functions differ between the lateral and medial vestibulospinal tracts?

Answer 24

lateral = ipsilateral connection, excitatory only

medial = bilateral connection, excitatory and inhibitory

Question 25

The lateral vestibulospina tract causes adjustment of the proximal limbs and trunk musculature by ___ of the extensor msucles and ___ ____ of the flexor muscles.

Answer 25

contraction of extensors

indirect relaxation of the flexors

Question 26

Conductive hearing loss is an issue with what part of the ear? Sensorineural?

Answer 26

conductive: external and middle
sensorineural: inner - usually the cochlea

Question 27

In the Weber test, to what ears will the sound lateralize in conductive loss? sensorineural loss?

Answer 27

conductive = will lateralize to the affected side (don’t have air conduction masking anything on that side, so it’s louder)

sensorineural = will lateralize to the unaffected side

Question 28

Talk about the signal pathway in the VOR if you turn you rhead to the left.

Answer 28

1. turn head to the left
2. left semicircular canal depolarizes, right hyperpolarizes
3. activation of the left medial and superior vestibular nuclei with inhibition on the right
4. the left vestibular nuclei project to the left eye medial rectus and the right eye lateral rectus, activating them. the right vestibular nuclei projects to the left eye lateral rectur and right eye medial rectus, inhibiting them
5. the eyes turn to the right

Question 29

In what tract do the neurons from the right and left medial nad superior vestibular nuclei cross to supply the extraoccular muscles?

Answer 29

the mediolateral funusculus

Question 30

Nystagmus consists of a slow drift in one direction called the ___ followed by a rapid recobery in the opposite direction called the ____

Answer 30

pursuit

saccade

Question 31

Which does the VOR control - the pursuit or the saccade? How about the cortex?

Answer 31

the VO controls the pursuit while the cortex controls the saccade

Question 32

Which part, the pursuit or saccade, is the nystagmus named for?

Answer 32

the saccade (even though the issue is typically in the VOR, not the cortex)

so in a right horizontal nystagmus, the VOR pursuit is to the left and the cortex saccade correction is to the right