Vestibular System

Question 1

In what bone is the vestibular apparatus located?

Answer 1

Petrous portion of temporal bone.

Question 2

How do canals pair themselves and why?

Answer 2

Posterior left with anterior right because they run in parallel planes (~45 from sagittal).

Question 3

T/F: the cupula is exposed to the endolymph?

Answer 3

True.

Question 4

Canals detect ___ acceleration and saccule / utricle detect ___ accel. The endolymph moves ___ the motion of rotation.

Answer 4

Angular, linear, opposite.

Question 5

What happens to the firing rate when the stereocilia bend toward the kinocilium? What about away?

Answer 5

Depolarization, increased firing rate (+).

Hyperpolarization, decreased firing rate (-).

Question 6

Due to voltage gated reciprocal opening and closing of Ca++ and K_ channels, the hair cells have a base firing rate of ____?

Answer 6

80-100 spikes/sec.

Question 7

T/F: kinocilium are most medial in the cupula?

Answer 7

True. Located at the top of the ring for visualization purposes.

Question 8

If the head rotates left there is a ___ firing rate on the right and ___ firing rate on the left.

Answer 8

Increase, decrease.

Question 9

What is the upper limit for velocity detection for half the apparatus in the vestibular system?

Answer 9

180*/sec.

Question 10

To where does the otolith transmit head position?

Answer 10

Cerebral cortex - insular and parietal lobes.

Question 11

What are the otoliths better at detecting slow speeds?

Answer 11

More sensitive to pull of gravity due to gelatenous masses and tonic firing rate.

Question 12

T/F: CN VIII is unipolar neuron.

Answer 12

False, bipolar neuron.

Question 13

The superior division of CN VIII innervates ___ and the inferior division innervates ___.

Answer 13

SUPERIOR = lateral and anterior SCC, utricle and small portion of saccule.

INFERIOR = posterior SCC and remainder of saccule

Question 14

What is the blood supply to the vest. app.?

Answer 14

Labyrinthine from AICA or basilar. AICA and PICA

Question 15

What is the processing apparatus for the vest. sys? What about outputs?

Answer 15

Vestibular nuclei.

VOR (via MLF)
V-S tract (postural response)

Question 16

Where are the vestibular nuclei found?

Answer 16

Lateral recesses of 4th ventricle in rostral medulla and caudal pons.

Question 17

Vestibular nuclei efferents can modify hair cell firing rates. What are the descending and ascending projections to?

Answer 17

DESCENDING
medial and lateral V-S tract

ASCENDING
via MLF to CN III, IV, VI for eye movement
via thalamus to cortex for sensation

Question 18

Where does MLF pass from and to and what does it connect?

Answer 18

vest. nuc. to CN III, IV, VI from medulla to midbrain. one on each side of brainstem.

Question 19

T/F: both the medial and lateral V-S tract travel through the whole cord.

Answer 19

False, medial is only cervical.

Question 20

What lobe of the vestibulocerebellum coordinates output and reflexes?

Answer 20

Floculonodular lobe.

Question 21

What is the role of the reticular formation in vestibular sense?

Answer 21

It’s a central processing mechanism that helps integrate visual and somatosensory info with vest.

Question 22

The goal of the vestibulospinal reflex (VSR) is to maintain postural stability, with it’s primariy stimulus being head tilt (otoliths). List its 4 components / roles.

Answer 22

1. Responds to head tilting and gravity
2. Extensor response on side to which is is inclined.
3. Flexor response to opposite side.
4. Vest. sys. contributes to all postural responses (e.g. ankle / hip strategy).

Question 23

What components does an effective VOR depend upon?

Answer 23

1. Accurate peripheral input
2. Effective vestibular drive of eye movement
3. Intact cranial nerves for eye movement
4. Coordination by cerebellum

Question 24

Where is the abducens nucleus located?

Answer 24

Caudal pons.

Question 25

Describe the pathway of horizontal VOR eye muscle recruitment to compensate for a right head rotation.

Answer 25

Excitement of right vest. app., CN VIII efferent through vestibular nuclei in rostral medulla and caudal pons up MLF to abducens nuclei in caudal pons; recruitment of CN VI and interneuron to CN III.

Question 26

Which side are medial and lateral rectus recruited with a left head rotation?

Answer 26

left medial, right lateral

Question 27

How does VOR eye movement correlate to canal orientation?

Answer 27

Each canal a pair of eye muscles that creates a movement equal and opposite to what they detect via the oculomotor nuclei.

Question 28

The cervico-ocular reflex contributes to gaze stabilization in 15% of cases. From where does it receive input? Where does it send that information?

Answer 28

Cervical facet joint receptors. Vestibular nuclei > oculomotor nuclei

Question 29

The goal of optokinetic nystagmus is to keep a moving image fixed on the retina with a still head. What are the fast movements and what area in the midbrain does the signal travel though?

Answer 29

Saccades, pretectal midbrain.

Question 30

T/F: pathological nystagmus can be spontaneous, positional or gaze evoked.

Answer 30

True.

Question 31

Nystagmus is named in the direction of the fast component (saccade). Why does it occur with spinning (pathologically)?

Answer 31

With head turn right, eyes slowly track back in opposite direction until reaching end in orbit, then reset (fast) to midline. With spinning (continued turning), they will track right again and reset at end of ROM. Stops when endolymph catches up to speed of spinning.

Question 32

What happens to nystagmus when spinning stops?

Answer 32

Occurs in opposite direction (opposite spinning).

Question 33

Define vertigo.

Answer 33

Having a sense of moving when still.

Question 34

What are the 3 categories of peripheral disorders?

Answer 34

1. Reduced (hypo) function - receptors or nerve - uni or bilateral - complete or incomplete - treatable 2. Distorted function - mechanical malfunction - stimuli transduced incorrectly - treatable 3. Fluctuating function - input is present but fluctuates - episodic - uni or bilateral - least amenable to PT (unstable CNS, hard to adapt)

Question 35

What is a common pathology of acute unilateral hypofunction?

Answer 35

- Vertigo | - Spontaneous nystagmus

Question 36

What would happen with a right side lesion?

Answer 36

Spinning left with nystagmus left. Spinning because no input relative to 80-100 spikes/s on right (relatively excited), feels like induced motion. CNS adapts within days.

Question 37

T/F: Post vestibular neuritis is the most common cause of vertigo. What are its symptoms?

Answer 37

False, 2nd most common. Severe rotational vertigo, spontaneous horizontal nystagmus, imbalance, nausea. Resolves in 6 weeks (better with vest. exer).

Question 38

Stroke, neuritis, ototoxicity, trauma and post-op acoustic neuroma are acute types of peripheral hypofunction. Name the chronic types.

Answer 38

- age related - cumulative effects of Meniere's - recurrent neuritis

Question 39

What does the CNS do to compensate for per. hypof?

Answer 39

1. Increase sensitivity to remaning 2. reinterpret asymmetrical input 3. Increase visual and somato. input 4. Develop compensatory mechs.

Question 40

T/F: Older adults with vestibular dysfunction are most dependent on SS input.

Answer 40

False, vision.

Question 41

BPPV is most common vertigo. How is it usually experience for the pt? What is the direction of the nystagmus?

Answer 41

With some head movements, usually affected ear down. Nystagmus in same plane as affected canal.

Question 42

What direction is the nystagmus if the posterior canal is affected?

Answer 42

Torsional or vertical.

Question 43

Define canalithiasis and cupulolithiasis.

Answer 43

CUPO - part of otoconia from utricle in canal, sticks to cupula - little or not latency to nystagmus CANAL - debris in canal - longer latency to nystagmus

Question 44

What is the most common canal involved in BPPV? Why?

Answer 44

Posterior. Ampulla in below the utricle; debris easily comes in when membrane blocking decreases in size.

Question 45

What do frenzel lenses do?

Answer 45

Magnify eyes making it easier to see nystagmus. Prevents patient from visually fixating and supressing nystagmus.

Question 46

How do you treat distorted function?

Answer 46

Disoldge debris.

Question 47

Describe Meniere's disease.

Answer 47

Abnormal endolymphatic sac fxn. -expands and puts pressure on nerve Can result in hearing loss w/ acute symptoms resolving in 24-36 h. Days to weeks for recovery. Cum. loss over time.

Question 48

A perilymph fistula can occur between middle ear and perilymph. What causes it?

Answer 48

Head trauma, barotrauma, surgery, penetrating injury.

Question 49

During a dix-hallpike maneuver, which side is the fast component of nystagmus towards in a positive test?

Answer 49

The side with the ear closer to the ground (affected ear).

Question 50

In a positive BPPV test, which canal would an upbeat and downbeat nystagmus implicate?

Answer 50

UPBEAT -posterior SCC of tested side DOWNBEAT -anterior SCC of tested side

Question 51

List the 4 possible etiologies of CNS damage for central disorders.

Answer 51

1. Wallenberg's syndrome 2. Tumor 3. Aging 4. Trauma

Question 52

Name 2 unique symptoms of central lesions.

Answer 52

1. Resting spontaneous nystagmus - impairment of gaze fixation 2. Gaze evoked nystagmus - neural regular at end of saccade or smooth pursuit

Question 53

With central lesions, can you cancel VOR? That is, move you gaze with head?

Answer 53

No. Brainstem mechs above vestibular nuclei.

Question 54

What does a negative Dol's head maneuver demonstrate/indicate? How is it found?

Answer 54

Damage at lower brainstem level near mechanism for VOR. Holding eyelids open and moving rapidly in rotation, eyes remain fixed in midposition.

Question 55

What is the main difference in central vs peripheral nystagmus?

Answer 55

Nystagmus fatigues in peripheral problems. Eventual CNS compensation.

Question 56

What are the most common types of vestibular lab tests?

Answer 56

Function tests: positional and caloric.

Question 57

What direction of saccade is normally tested in caloric stimulation?

Answer 57

Horizontal.

Question 58

Caloric tests are good at detecting differences in vest. fxn between sides. What are rotational tests better at?

Answer 58

Bilateral dysfunction. Only tests horizontal SCC and posterior portion of superior vestibular n.

Question 59

What is the otolith test associated with?

Answer 59

Ocular torsion

Question 60

What does adaptation refer to in vestibular rehab?

Answer 60

Increasing the gain of the VOR. - peripherally - centrally (more important)

Question 61

Name two pathological symptoms that present with acute central adaptation.

Answer 61

Vertigo, nystagmus gone in days.

Question 62

Name some central adaptations.

Answer 62

Increasing VOR gain, fine tuning VSR and other balance reactions. Peripheral and central, cerebellar F-N lobe.