Exam 3 Week 14 ppt 11 & 12 Vestibular Central Connections Part 1 & 2

Question 1

what type of neurons are the primary afferent fibers leaving the macular and ampular epithelium (macular organs and ampular organs)?

Answer 1

bipolar neurons

Question 2

Where do the primary afferent fibers of the bipolar neurons leaving both the macular and ampular epithelium have their cell bodies?

Answer 2

•The maculae and cristae are innervated by bipolar neurons of the vestibular (Scarpa’s) ganglion

Question 3

what nerve does the central process of the first order neurons from the macular and ampullar epithelium form?

Answer 3

The central processes of these bipolar neurons form the vestibular nerve

Question 4

where does the vestibular nerve enter the brainstem?

(and what nerve was it part of)

Answer 4

enters the brain stem at the pontomedullary junction just medial to the acoustic portion of the vestibulocochlear nerve (CN VIII)

Question 5

Where are the four vestibular nuclei found?

Answer 5

at the pontomedually junction

Question 6

List the four vestibular nuclei:

Answer 6

1. -Lateral vestibular nucleus
2. -Inferior vestibular nucleus
3. -Medial vestibular nucleus
4. -Superior vestibular nucleus

Question 7

Where do the vestibular nuclei get input from? (3)

Answer 7

1. Vestibular nerve
2. Cerebellum
3. Other inputs

Question 8

what does SSC stand for?

Answer 8

semi-circular canal

(not sure why it is SSC and not SCC)

Question 9

what does the vestibular nerve bifurcate into?

Answer 9

-Bifurcates into short ascending and long descending branches to the vestibular nuclei.

Question 10

Vestibular nerve: Which nuclei do inputs from the semicircula canals primarily go to?

What do they also sometimes go to?

Answer 10

-Semicircular canals inputs go primarily to

1. medial vestibular nuclei
2. superior vestibular nuclei

some go to

1. lateral vestibular nuclei
2. inferior vestibular nuclei

Question 11

Vestibular Nerve: Which nuclei do inputs from maculae primarily go to?

Answer 11

-Macular inputs go primarily to the:

1. lateral vestibular nuclei
2. medial vestibular nuclei
3. Inferior vestibular nuclei

Question 12

what vestibular nuclei are related to eye movements?

what has major inputs into these nuclei?

Answer 12

1. medial vestibular nuclei
2. superior vestibular nuceli

-Semicircular canals inputs go primarily to medial and superior vestibular nuclei

Question 13

what vestibular nuclei are closely related postural adjustments?

what has major inputs into these nuclei?

Answer 13

1. lateral vestibular nuclei
2. medial vestibular nuclei
3. inferior vestibular nuclei

-Macular inputs go primarily to the lateral, medial and inferior vestibular nuclei

Question 14

does the vestibular nuclei receive input from the cerebellum?

Answer 14

Yes!

Just as there are projections from the vestibular nerve and nuclei into the cerebellum there are Cerebellar projections to vestibular nuclei

Question 15

Where do the cerebellar projections to the vestibular nuclei travel?

where do they come from?

and are they inhibitory or excitatory?

Answer 15

Travel through the inferior cerebellar peduncle to all nuclei

Cerebellar cortex of flocculonodular lobe: Inhibitory

Fastigial nucleus: Excitatory

These projections to and from the cerebellum go through the inferior cerebellar peduncle to all vestibular nuclei. There are Inhibitory projections from cerebellar cortex of flocculonodular lobe and Excitatory projections from the fastigial nucleus.

Question 16

do any fibers from the semicircular canals travel to somehwere outside of the vestibular nuclei?

if so where?

Answer 16

-Some fibers from SSCs rise directly thru inferior cerebellar peduncle into the cerebellum

1. End in the nodulus and perhaps the floccular cortex
2. Collaterals end in the fastigial nucleus

Some fibers from semicircular canals rise directly thru inferior cerebellar peduncle into the cerebellum to End in the nodulus and perhaps the floccular cortex with Collaterals ending in the fastigial nucleus

Question 17

are there any additional connections involving vestibular nuclei besides the primary afferent and cerebellar inputs?

If so, what are they?

Answer 17

Yes

There are Commissural Connections

Question 18

what are the commussural connections between?

Answer 18

there are considerable Commissural Connections Between most of the nuclei but

most prominent between the contralateral

1. medial vestibular nuclei and
2. superior vestibular nuclei.

Question 19

are the commissural connections primarily inhibitory or excitatory?

why?

Answer 19

. These commissural connections are Primarily inhibitory so increased activity on one side inhibits activity on the other. Remember of course that vestibular input is bilateral – cannot accelerate one side of head & not other.

Question 20

describe what happens in relationship to the vestibular commissural connections when the head rotates right.

Answer 20

• Right vestibular nuclei more 1° afferent excitation
• Left vestibular nuclei less 1° afferent excitation
• Commissural connections will match this pattern of input to the vestibular nuclei so works together with 1° afferent input

So with say rotation to the right, the right vestibular nuclei will have additional excitation by the primary afferents and the left vestibular nuclei will receive less excitation. The excited right vestibular nuclei will produce inhibition of the left vestibular nuclei and there will be less inhibition of the right vestibular nuclei by the left vestibular nuclei. So you can see that the vestibular primary afferents and commissural connections work together

Question 21

why are commissural Connections of the vestibular nuclei imortant? (2)

Answer 21

1. -Important for comparison of activities of the pairs of semicircular canals and macular structures
2. -Mechanism by which compensation can occur for unilateral vestibular damage

Commissural Connections are Important for comparison of activities of the pairs of semicircular canals and macular structure. With the similarity of function of commissural connections to that of the primary afferent input, these commissural connections are a Mechanism by which compensation can occur for unilateral vestibular damage

Question 22

what are some other inputs to the vestibular nuclei besides commissural, primary afferents, and cerebellar inputs?

Answer 22

-Some inputs from spinal cord & brainstem complete the picture

There are also Other Inputs to Nuclei as there are Some inputs from spinal cord & brainstem complete the picture

Question 23

Where do central projections from the vestibular nuclei go?

Answer 23

•Projections from Vestibular Nuclei to Thalamus & Cerebrum

• -Projections from superior, medial & lateral vestibular nuclei to ventroposterolateral (VPL) nucleus of thalamus

Now for the conscious awareness of head position and acceleration there are vestibular nuclearProjections from Vestibular Nuclei to Thalamus & Cerebrum. However this is the Least robust of any sensory system

There are Projections from superior, medial & lateral vestibular nuclei to ventroposterolateral (VPL) nucleus of thalamus

Question 24

how does the vestibular system compare to other sensory systems in its strength of central connections?

Answer 24

the vestibular system is the Least robust of any sensory system

Question 25

Are projections from the vestibular nuclei ipsilateral, contralateral, or bilateral?

what does this result in?

Answer 25

-Projections bilateral to thalamus so activity bilaterally represented in cerebral cortex

Projections from the vestibular nuclei to the thalamus are bilateral so activity is also bilaterally represented in cerebral cortex.

Question 26

How many cortical areas receive projections from the VPL nucleus of the thalamus from the vestibular system?

Answer 26

4

Question 27

What are the four cortical areas that receive projections from the VPL nucleus of the thalamus from the vestibular system?

Answer 27

The projections from the ventroposterolateral (VPL) nucleus of thalamus are to 4 cortical areas related to vestibular function in insula and parietal lobe

Question 28

what are the functions of the cerebral vestibular areas?

Answer 28

• -Sense of body & head position but not be a perceptual necessity
  
  • -We usually rely more on Vision for the sense of movement
  • -We usually rely more on Proprioception for sense of position
  • -This Same priority pattern is seen in balance & reflexes

Cerebral Vestibular areas plays a role in sense of body & head position but not normally cued into it as perceptual necessity. We are more perceptually cued into vision and proprioception. We rely on vision more for the sense of movement, then proprioception and then vestibular sensation. We rely on proprioception more for the sense of position along with vision. We see the same priorities for balance reflexive responses as well

Question 29

are there connections between the reticular formation and the vestibular nucei?

Answer 29

Yes

There are strong connections between the vestibular nuclei and the Reticular Formation.

Question 30

Describe the connections between the Reticular formation and the vestibular nuclei?

include function

Answer 30

1. -Vestibular nuclei Connections with UMN of reticulospinal tracts –
   
   • complementary to vestibulospinal tract control of balance & posture
2. -Vestibular Connections through RF to hypothalamus
   
   • for control of autonomic responses to vestibular input
     
     • -Nausea, vomiting, pallor and perspiration associated with overstimulation of vestibular system or vestibular system damage

There are strong connections between the vestibular nuclei and the Reticular Formation. There are Connections with UMN of reticulospinal tracts which are complementary to vestibulospinal tract control of balance & posture. There are also Connections through RF to hypothalamus for control of autonomic responses to vestibular input. Nausea, vomiting, pallor and perspiration associated with overstimulation of vestibular system or vestibular system damage

Question 31

Describe the function of the vestibular connection with UMN of reticulospinal tracts:

Answer 31

• Vestibular nuclei Connections with UMN of reticulospinal tracts:
• complementary to vestibulospinal tract control of balance & posture
• Vestibular Connections through RF to hypothalamus

for control of autonomic responses to vestibular input

-Nausea, vomiting, pallor and perspiration associated with overstimulation of vestibular system or vestibular system damage

Question 32

Describe the function of the vestibular connections through the RF to the hypothalamus

Answer 32

-Vestibular Connections through RF to hypothalamus

• for control of autonomic responses to vestibular input
  
  • -Nausea, vomiting, pallor and perspiration associated with overstimulation of vestibular system or vestibular system damage

There are also Connections through RF to hypothalamus for control of autonomic responses to vestibular input. Nausea, vomiting, pallor and perspiration associated with overstimulation of vestibular system or vestibular system damage

Question 33

Describe the vestibular connections to the cerebellum

Answer 33

1. -Direct projection of 1° afferents into cerebellum thru inferior cerebellar peduncle
2. -Projections from vestibular nuclei
   
   • Come form most nuclei
   • Through the inferior cerebellar peduncle
   • Vestibulocerebellar projections go primarily to flocculonodular lobe & uvula with collaterals going to the fastigial & dentate nuclei and other areas of cortex
   • For balance, reflexes and movement coordination

We have mentioned before the connection of the vestibular nuclei with the flocculonodular lobe of the Cerebellum. As we have mentioned previously there are Direct projection of 1° afferents and Projections from most vestibular nuclei into cerebellum thru inferior cerebellar peduncle. Vestibulocerebellar projections go primarily to flocculonodular lobe with collaterals going to the fastigial & dentate nuclei and some other areas of cortex. These connections are for balance, reflexes and movement coordination

Question 34

what do the lateral and medial vestibular nuclei give rise to?

Answer 34

Two UMN descending tracts

• lateral vestibulospinal tract (LVST)
• medial vestibulospinal tract (MVST)

Then there is the vestibulomotor system with the lateral and medial vestibular nuclei having upper motor neurons which give rise to the the descending lateral and medial vestibulospinal tracts

Question 35

What is the vestibulomotor system?

Answer 35

Then there is the vestibulomotor system with the lateral and medial vestibular nuclei having upper motor neurons which give rise to the the descending lateral and medial vestibulospinal tracts

Question 36

Describe the anatomy of the Lateral Vestibulospinal tract (4)

Answer 36

•Lateral vestibulospinal tract (LVST)

• –Arises from lateral vestibular nucleus
• –Larger of the two tracts
• –Excitatory to ipsilateral spinal cord extensor nuclei
• –Biggest input is from the cerebellum

Lateral vestibulospinal tract (LVST) Arises from lateral vestibular nucleus, is the Larger of the two tracts with Excitatory primarily ipsilateral effects on spinal cord extensor nuclei throughout the spinal cord. The biggest input is from the cerebellum but remember there are also considerable inputs form the macular epithelium and some input from the semicircular canals into the lateral vestibular nucleus

Question 37

What is the function of the Lateral Vestibulospinal Tract?

Answer 37

•Lateral vestibulospinal tract (LVST)
–Facilitates and maintains extensor tone in limbs and trunk – antigravity response

Question 38

LVST

Answer 38

Lateral Vestibulospinal Tract

Question 39

Describe the anatomy and function of the Medial Vestibulospinal tract (4)

Answer 39

•Medial vestibulospinal tract (MVST)

1. –Descends from medial vestibular nucleus
2. –Functionally descends only to the cervical spinal cord
3. –Functions to stabilize the head in space when the body is moving when walking around
4. –Functions to stabilize the eyes (& head) and maintain gaze during body movements

Medial vestibulospinal tract (MVST) Descends from medial vestibular nucleus primarily to the cervical spinal cord and Functions to stabilize the head in space when the body is moving when walking around. Also the Medial vestibulospinal tract (MVST) Functions to stabilize the eyes (& head) and maintain gaze during body movements.

Question 40

MVST

Answer 40

Medial Vestibulospinal tract

Question 41

Describe the Vestbiular nuclei projections to extraocular motor neurons:

name

pathway

function

Answer 41

• They are called the Medial Longitudinal Fasciculus
• •projections from the superior and medial vestibular nuclei project to nuclei of CN III, IV, VI
• •Coordinate eye movement with body movement or head movement (vestibulo-ocular reflex)

Vestibular nuclei also Projections to Extraocular Motor Neurons. Medial Longitudinal Fasciculus (MLF) projections from the superior and medial vestibular nuclei project to nuclei of CN III, IV, VI. . The MLF has a laterality pattern but effect projects bilaterally

These vestibular projections to the extraocular lower motor neuron nuclei are important for Coordinate eye movement with body movement or head movement (vestibulo-ocular reflex). We will talk more about this function in a later video.

Question 42

MLF

Answer 42

Medial Longitudinal Fasciculus