week 5- Vestibular system

Question 1

are vestibular cells unipolar or bipolar?

Answer 1

bipolar

Question 2

what 2 types of information does the vestibular system provide?

Answer 2

 How head is oriented in space  Whether the head is moving

Question 3

What saccade and what smooth pursuit does the left hemisphere control

Answer 3

Left controls smooth pursuits to the Left via the parietal occipital region, and saccades to the Right via the FEF

Question 4

What would result with damage to the right FEF

Answer 4

right gaze preference since the left FEF is unopposed… The eyes CAN move left as part of smooth pursuit/tracking maneuver. Can also move left as part of brainstem mediated reflexive response. It is only the voluntary actions that require the FEF to be affected

Question 5

compare OKN to VOR

Answer 5

OKN uses visual processing while VOR does not, it is a brainstem reflex and only responds to rapid input such as a jerky head reflex

in the vOR the brainstem is the slow movement while the FEF saccade is the fast return to center

Question 6

Outline what would happen when a cold caloric test is applied to the R ear from the vestibular nuclei to the MLF

also indicate what caloric test could be used for

Answer 6

Cold water in R ear

tells brain head turned to L so eyes look right

L vestibular nuclei activated

R abducens activated to pull R eye right

L MLF to activate L oculomotor and pull medial rectus

eyes look RIGHT with left beating nystagmus

(COWS cold opposite, warm same nystagmus)

this can be used in uncouncious PTs to determine if they are brain dead, but also in concious PTs to determine if there is dysfunction at any of the above mentioned levels

Question 7

In the VOR cold caloric test what would happen cerebral cortex was damaged

Answer 7

Brainstem ok: VOR towards cold ear is intact

Cerebral cortex impairment: Saccade back to center is impaired

Final result:VOR causes deviation of eyes towards cold ear and they stay there

Question 8

Cold caloric result to right ear if brainstem is ok but right abducens axon is impaired

Answer 8

Brainstem ok: VOR towards right cold ear is intact BUT…

Right abducens axon impairment: right lateral rectus is impaired, right eye cannot abduct right, but left eye medial rectus is fine and left eye adducts rightwards

Question 9

what axons enter at ther cerebellopontine angle

Answer 9

VII and VIII into the internal aucoustic canal

Question 10

differentiate the Static labyrinth vs the kinetic

Answer 10

Static labyrinth: utricle and saccule detect linear acceleration(gravity)

• macula of the utricle is horizontal, while the saccule if verticle

Kinetic labyrinth: semicircular canals detect angular acceleration

There are 3 pairs of semi-circular canals

1. Horizontal left + horizontal right
2. Anterior left + posterior right
3. Anterior right + posterior left

Question 11

Outline the process of stereocillia activation

Answer 11

detect movement of endolymph –> movement toward taller one ( kinocilium ) –> increase K form the K high endolymph into the inside of the hair –> K sent out to the perilymph and ca enters to facillitate the SNARE vesicle release of GLU–> increased firing rate of CN VIII sensory (afferent) axons

there is some GLU leakage at rest

Question 12

Outline some peripheral causes of vertigo

outline some central causes

outline some systemic causes

Answer 12

peripheral: Labyrinthitis, acoustic neuroma, BPPV, Meniere’s disease (inner ear labyrinth or vestibular nerve)

central: brainstem, cerebellum, cerebral cortex

systemic: metabolic or CV

Question 13

what are some general differences that you may see in a central versus a peripheral cause of vertigo

Answer 13

Peripheral:

spontaneous horizontal nystagmus that occurs after 3-10 secs

doesn’t change direction

and is fatigable

auditory involvement (tinnitus, deafness), nausea, vommitting

Central:

spontaneous IMMEDIATE nystagmus

that changes direction

and in NOT fatigable

vertical nystagmus (lesion to midbrain likely due to location of vertical gaze center)

rotary nystagmus

no nausea

Question 14

what is benign paroxysmal peripheral vertigo BBPV caused by

clinical indications

how do you test it

how do you fix it

Answer 14

Problem is that otolith have shaken loose from the static labyrinth and ended up in the semicircular canal which becomes over-stimulated –> vertigo

clinical indications: episodic vertigo

test: Dix-Hallpike: provocative maneuver
fix: Epley maneuver

Question 15

what is menieres disease

cause and the clinical hallmarks

Answer 15

cause:

increased endolymph pressure

clinical hallmarks

violent, sudden attack, vertigo lasting 1 - several hours, tinnitus, deafness, Nausea, vomiting, Nystagmus lasting 1-2 hours per attack

Question 16

what is the cause and the hallmarks of vestibular schwannoma

Answer 16

cause:

Schwann cell tumor originating on vestibular portion of CN 8

hallmarks:

vertigo/dizziness, nausea, nystagmus, ipsilateral facial paresis/paralysis,

loss of corneal reflex,

loss of taste (front 2/3 of tongue),

loss of salivation, tearing

hyperacusis with facial nerve nerve damage? No! overridden by deafness!

Cerebellar signs possible

Brainstem auditory evoked responses (BAER) are a very sensitive test

Question 17

1. You are rounding on patients during your Neurology clerkship. You meet a man who was admitted two days ago following a stroke. You note that he has paralysis of his left arm and weakness of his left leg. His tongue deviates to the left on protrusion. His eyes are deviated a bit to his right, but he can look over at you when you stand to his left and speak to him.

Occlusion of branches of which artery would best explain these findings?

Answer 17

Right MCA –> contra body

Right MCA –> right UMN for hypoglossal = contra tongue

Right MCA –> right FEF –> to move the eyes to the left. With this gone = remaining left FEF continues to drive the eyes to the right, resulting in a right gaze preference

Question 18

You test your patient’s VOR by asking them to look at your finger that you hold directly in front of them. You then ask them to RAPIDLY turn their head to the right while continuing to focus on your finger. You then ask them to bring their head back to center and then to RAPIDLY turn their head to the left, while continuing to focus on your finger.

You observe the following:

On rapid head turn to the right, their left eye and right eye both shift left.

On rapid head turn to the left, their left eye shifts right but their right eye does not respond.

Damage involving which of the following locations would best explain these findings?

Answer 18

Damage to right abducens nucleus àno R LR. But the best answer would be damage to the R pontine BASE since the dorsal medial pons would include the nucleus = also MLF

Question 19

what would lateral medullary syndrome result in

Answer 19

PICA occlusion – lateral medullary syndrome

Spinothalamic tract – contralateral

Spinal trigeminal- ipsilateral

Descending sympathetic fibers- ipsilateral horners syndrome

Nausea, vertigo limb ataxia- ipsilateral from cerebeleum inferior peduncle and vestibular nuclei

Question 20

align each symptom with the correct area of dysfunction

Parkinson

ataxia

spastic gait

dystrophic

slapping

Answer 20

BG dysfunction- Parkinson

Cerebellar- ataxia

UMN- spastic (chronic), flaccid (acutely)

Muscle- dystrophic

Peripheral neuropathy- slapp

Question 21

indicate the role of the rubrospinal tract

tectospinal tract

reticulospinal

vesticulospinal

Answer 21

rubrospinal tract: excites distal flexors

tectospinal tract :Turn head to a stimulus

reticulospinal: Feed forwardàPostural adjustments in anticipation of voluntary movements to maintain balance & stabilityby axial muscles and proximal limb extensors

vesticulospinal: Feed back àActivated by fast movements such as slipping, NOT star gazing

Question 22

where are the cell bodies of the

rubrospinal tract

tectospinal tract

reticulospinal

vesticulospinal

Answer 22

rubrospinal tract: red nuclues of midbrain (right below STN and above SN

tectospinal tract: tectum of the midbrain

reticulospinal: pons and medulla
vesticulospinal: pons and medulla

Question 23

where does the vestibulospinal tract send projections to and from

Answer 23

Receives projections from:
§ Flocculonodular lobe of cerebellum
§ Static and Kinetic labyrinths via CN VIII

§ Contralateral vestibular nucleus
§ Spinal cord (proprioception)

oProjects to
§ Cerebral cortex via thalamus
§ Flocculonodular lobe of cerebellum

§ Contralateral vestibular nucleus

§ Spinal cord

• Alpha and gamma MNs via MVST
• Ipsilateral limb extensors via LVST

Adjusts head, eye coordination and excites limb extensors

integrate informationabout the position of the head in space (via the labyrinth) AND the position of the body (via proprioception

Lean to the LEFT–>

Excite LEFT labyrinth –>

LEFT CN VIII –>

excites LEFT Vestibular nucleus –>

LEFT lateral VST –>

LEFT side extensors

Question 24

describe Decorticate and decerebrate posturing

Answer 24

Decorticate and decerebrate posturing= both tell you that only the brainstem is working

Decorticate

Flexor bias in limbs because lesion is above the midbrain red nucleus so it cannot provide feedback

Decerebrate

Lesion between red nucleus and vestibular nucleus which means loss of flexor bias now BUT the vestibular nucleus can now do what it wants without overtone = extension of arms and legs