Vestibular Flashcards by Dave Ed

What are the 3 general “balance” systems and how many at a time are essential for balance?

Vestibular, proprioceptive, and visual systems

- 2 out of 3

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What are the 3 main structural parts of the vestibular apparatus?

Semicircular canals (SSCs)- ant/horizontal/post
Utricle- connects the 3 canals
Saccule- continuous w/the cochlea

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What is the main things that the semicircular canals measures?
Utricle?
Saccule?

SSC: Angular/rotational motion
Utricle: Primary gravity sensor (upright position/head tilt); horizontal linear accelleration
Saccule: Detects general orientation and vertical linear accelleration

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What’s the name of the part of the semicircular canals that contains the hair cells?
What’s the name of the gelatinous substance covering the hair cells?

Ampulla

- Cupula

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What is the physics term for why the hair cells bend w/head rotation?
How sensitive are they?

Inertial displacement, sensitive to accelleration (not velocity)
- 0.1 degree/sec^2 (very)

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Generally explain how inertial displacement affects the cupula.

Movement of the head results in an inertial displacement of the fluid, pushing the cupula in the opposite direction in the canal

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How does inertial displacement affect perception?

Differential displacement of the hair cells on the left and right horizontal canals causes the cortex to perceive these corresponding increases and decreases in output as directional movement (left or right) with a specific “velocity.”
The greater the difference, the faster the perceived velocity.

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How does alcohol affect our perception during inertial displacement?

If you change relative output b/w the 2 sides (ETOH alters their conduction velocity), it’s perceived as movement…brain thinks you’re moving in that particular direction…vertigo

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Explain how the hair cells of the 3 canals are paired and how they’re oriented w/respect to the utricle.

Ant canal on R paired w/post canal on L. Ant canal on L paired w/post canal on R. Ant and post canals oriented away from the utricle.
Horizontal canals are paired, oriented toward the utricle.

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How many stereocilia and kinocilia are their per hair cell in the SSC?

1 large kinocilium

- 40-70 stereocilia (linked to the kinocilium)

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How are hair cells depolarized/hyperpolarized?

Bending towards kinocilium causes depolarization (AP more likely). Bending away causes hyperpolarization. Bending perpendicular has no effect.
Gives hair cell orientation axis.
They have tonic output; never give off APs (AP occur in bipolar cells of vestibular n.).

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What is the main difference b/w the tectorial membrane of the cochlea and the cupula covering the hair cells of the utricle and saccule?
What’s the functional reason?

Contains otolithic granules (Ca carbonate crystals), known as otolithic membrane.
- Allows perception of gravity–changes w/head position

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Explain the pw of input from a hair cell to the CNS.

*Hair cell > bipolar cell (AP) > vestibular ganglion > CN VIII > vestibular nuclei

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Is the posterior saccule and posterior SCC in the inferior or superior division of the vestibular ganglion?
What’s in the other ganglion?

Inferior division (everything else is in superior division)

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On cross section, where on the brainstem would you find the vestibular nuclei?

*Rostral medulla/caudal pons, posterior and medial to inferior cerebellar peduncles

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*What do the ascending fibers of the medial longitudinal fasciculus (MLF) control?
What else is important about the MLF’s functional relation the vestibular system?

Eye movements

- Connects III, IV, and VI to the vestibular system

What do the descending fibers of the medial longitudinal fasciculus control?

Head and neck movements

What part of the cerebellum is the vestibular system associated with?
What gives it direct input? What gives it indirect input?

Flocconodular lobe

Direct input from SSC and otolithic organs
Indirect input from vestibular nuclei, LGN, sup colliculus, and pontine nucleus

What are 2 main reasons why the cerebellum would send info back to vestibular nuclei?

To control axial and proximal limb muscles associated with balance and posture
To control eye movements and coordination of head & eye movements.

Lateral vestibulospinal tract:
Name the nucleus.
Crossed or uncrossed?
Length along sc?
What does it act on and why?

Lateral vestibulospinal nucleus
Uncrossed
Entire length of sc
Acts on proximal limb mm. to control balance

Medial vestibulospinal tract:
Name the nucleus.
Crossed or uncrossed?
Length along sc?
What does it act on and why?

Medial vestibulospinal nucleus
Uncrossed (bilateral)
Cervical sc only
Acts on neck mm. (head stays erect)

When we use the vestibular system to stabilize our gaze, what is the effector system?
What major parts of the brain are involved?

Extra-ocular mm.

- Vestibular system, cerebral cortex, cerebellum, brainstem

What is the function of the vestibular-ocular reflex (VOR)? How does it work?
What would happen w/o it?

Stabilizes the image on the retina during a rotation of the head *faster than visual tracking. As the head rotates the VOR rotates the eyes with the same speed, but in the opposite direction
W/o it, image would appear smeared on retina

What nucleus accounts for the image stabilization that occurs during the vestibulo-ocular reflex?

Nucleus prepositus hypoglossi

attenuates w/tonic stimulation

Explain what's happening at all levels of the VOR when the head is rotating to the right while looking at a stationary image.

* Both eyes will move to the left... - R horizontal canal is activated - R vestibular nucleus is activated - L CN VI nucleus is activated (via PPRF), L lateral rectus m. contracts - Left PPRF activates neurons in R CN III nucleus, R medial rectus contracts PPRF: Paramedian pontine reticular formation. Also, *MLF important for eye movement coordination.

Explain the basics of nystagmus.

- Definition: Rhythmic back-and-forth movement of eyes (often involuntary; usually horizontal but can be vertical or rotary) - Usually the movement is slow in one direction (“smooth”) and fast (“saccadic”) in the other

Explain the steps that occur in nystagmus when you induce it by spinning yourself around.

1. The VOR is generating the slow phase which helps to keep an eye on a target 2. Once the eye approaches the maximum that it can turn, a saccade will then occur moving the eyes in an opposite direction and onto a new target (Optokinetic nystagmus or OKN)

How do you test clinically for nystagmus?

Caloric test - Hot and cold water produce currents in opposite directions and therefore a horizontal nystagmus in opposite directions. - COWS: Cold Opposite, Warm Same. (fast phase) Cold water = FAST phase of nystagmus to the side Opposite from the cold water filled ear Warm water = FAST phase of nystagmus to the Same side as the warm water filled ear

Explain 3 ways we can become dizzy w/o illness?

1. Vestibular system activated w/o visual system (spin in chair w/eyes closed, vestibular system attenuates) 2. Sense of motion via visual system w/o vestibular confirmation - "a disconnect" (like in the automatic carwashes) 3. Sense of motion via vestibular system w/o visual confirmation - "a disconnect" (being in boat cabin during storm > motion sickness)

A virus invades the stria vascularis cells of the left inner ear, resulting in a significant increase in the concentration of potassium in the endolymph. Which one of the following would you expect to happen? A. The outer hair cells hyperpolarize, causing a high pitched “ringing” in the ears. B. The patient complains of muffled sounds due to smaller receptor potentials in the inner hair cells. C. The hair cells in the left ampulae depolarize to a greater extent than those on the right, and the patient complains of vertigo/dizziness. D. The otoconia hyperpolarize, and the patient feels “light-headed.”

C. The hair cells in the left ampulae depolarize to a greater extent than those on the right, and the patient complains of vertigo/dizziness.

When you voluntarily turn your head to the left, which one of the following events will occur in the vestibular system? A. Kinocilia in the ampullae of all the semicircular canals will be simultaneously activated. B. Movement of the stereocilia in the left horizontal canal move towards the kinocilia, resulting in depolarization of the hair cell. C. The medial and superior vestibular nuclei will be inhibited by the afferent fibers from the semicircular canals. D. The velocity of the movement is detected by the otolithic granules in the anterior and posterior semicircular canals. E. Compensatory eye movements will likely be inhibited by the descending MLF.

B. Movement of the stereocilia in the left horizontal canal move towards the kinocilia, resulting in depolarization of the hair cell.

Vestibular function is tested in a 19-year-old man using the caloric test. Assuming a normal outcome, which one of the following is most likely to occur when warm water is introduced into the man’s RIGHT ear? A. Horizontal nystagmus, fast phase directed left. B. Horizontal nystagmus, fast phase directed right. C. Occular counter-roll (eversion of eyeball) to the right. D. Vertical nystagmus, fast phase directed downward. E. Vertical nystagmus, alternating fast phases.

B. Horizontal nystagmus, fast phase directed right

Which of the following contain an otolithic membrane? - Semicircular canals - Utricle - Saccule

- Utricle | - Saccule