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Block 5 Week 2 Meg > Sievert: Vestibular > Flashcards

Sievert: Vestibular Flashcards

1
Q

What are the components of the vestibular apparatus?

A

3 semicircular canals to detect rotational movements

2 otolith organs, the utricle and the saccule, to detect linear accelerations and head tilts

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2
Q

Are there channels for endolymph and perilymph in the vestibular apparatus? What are the implications of this?

A

yes; any overproduction of endolymph will cause a problem both in the auditory and vestibular systems

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3
Q

What are the orientations of the 3 semicircular canals?

A

horizontal

anterior and posterior

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4
Q

What detects linear accelerations and head tilts?

A

utricle and saccule

*one is horizontal, one is vertical

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5
Q

Are there hair cells in the vestibular apparatus? Describe these hair cells.

A

Yes; similar to those in the auditory system; they have one kinocilium to the side and the rest are stereocilia, ion channels are bathed in the same fluids (endolymph/perilymph).

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6
Q

In the ampulla of the semicircular canals, where are the hair cells embedded?

A

imbedded in the cupula (a gelatinous mass) in the ampulla

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7
Q

How are hair cells in the cupula excited or inhibited?

A

excited or inhibited when fluid moves around the semicircular canal during rotations *excited when stereocilia are bent toward the kinocilium

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8
Q

In the utricle and the saccule, where are the hair cells embedded?

A

imbedded in the otolithic membrane with little stones on top called otoconia

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9
Q

What’s this?
lay on top of the otolithic membrane
move due to the effects of gravity or linear accelerations and cause the hair cells to fire

A

otoconia

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10
Q

How are hair cells in the ampulla oriented?

A

in the same direction along the striola

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11
Q

How are hair cells in the utricle and saccule oriented?

A

they oppose each other along the striola

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12
Q

What happens to fluid in the ear when you begin to spin in circles? What happens when you stop abruptly?

A

Initially, the fluid will lag and will spin in the opposing direction; however, it will eventually catch up. When you stop, the fluid will continue to spin in the same direction that you were spinning in for some time

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13
Q

What is a nice “landmark” in the brainstem for the special somatic afferent nuclei (dorsal and ventral cochlear nuclei)?

A

the inferior cerebellar peduncle

*these nuclei surround it

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14
Q

How many vestibular nuclei surround the inferior cerebellar peduncle?

A

four

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15
Q

What other random nucleus should you be aware of near the inferior cerebellar peduncle?

A

the spinal tract of CN5

*will be present everywhere from the pons down to the caudal medulla (and maybe even in the rostral spinal cord)

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16
Q

The hair cells in the inner ear have a connection to what ganglion? Basically, signals from the hair cells will reach what first?

A

the vestibular ganglion

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17
Q

Where do nerve fibers from CN 8 go after leaving the vestibular ganglion?
*recall, there is no synapse in this ganglion; it’s like a DRG

A

they go to the vestibular nuclei and from there they can go to a number of places!

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18
Q

What pathway takes CN 8 fibers from the vestibular nuclei to the upper spinal cord? Is this pathway bilateral or ipsilateral? What action do they have in the upper spinal cord?

A

medial vestibulospinal tract;
this is a bilateral path;
these fibers control the axial musculature involved in the head, neck, and upper trunk turning

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19
Q

What pathway takes CN 8 fibers from the vestibular nuclei to the spinal cord to control proximal anti-gravity muscles? Is this a bilateral or ipsilateral pathway?

A

lateral vestibulospinal tract; ipsilateral

*this tract helps maintain an upright balanced posture by stimulating extensor motor neurons in the legs

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20
Q

What muscles are activated in the anti-gravity response to the lateral vestibular tract?

A

quads, soleus, gastroc, gluteus

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21
Q

Fibers can also project from the vestibular nuclei to the (blank)

A

cerebellum

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22
Q

Fibers project from the vestibular nuclei to the (blank) via the thalamus to supply information for planning movements based on the position of the body in space.

A

parietal sensory cortex

23
Q

Fibers from the vestibular nuclei can project to the brainstem motor nuclei of which cranial nerves to coordinate eye movements with head movements (VOR)?

A

CN 3, 6, and 4

24
Q

What is the nucleus in the thalamus where some fibers may go after leaving the vestibular nuclei? What other information also goes to this nucleus?

A

VPL; inputs from the medial lemniscus about TVP (proprioception, vibration sense, etc)
*these merge with the input from the vestibular nuclei and they both pass on to the cortex

25
Q

What do the medial and lateral vestibulospinal tracts do?

A

help maintain posture when you slip on ice; projections to and from the cerebellum with info related to body position for proper coordination of future movements

26
Q

The medial and lateral vestibulospinal tracts are important for what two things?

A

VCR (vestibulo cervical reflex)

VSR (vestibulo spinal reflex)

27
Q

Projections from the vestibular nuclei to the cortex pass through the VPL of the thalamus. Does this occur bilaterally? Why? From the thalamus, where does this input go?

A

yes, occurs bilaterally, because this pathway tells you about the position of your body in space (so both sides need this information); this input then goes to the postcentral gyrus of the somatosensory cortex

28
Q

What nuclei are responsible for moving the eyes in the aBduction and aDduction direction?

A

abduction: nucleus of CN 6 (lateral rectus)
adduction: nucleus of CN 3 (medial rectus)

29
Q

Where must input coming out of the vestibular nuclei go before reaching nuclei of 3 and 6? What does this nucleus do?

A

a small nucleus that integrates information called the PPRF; the PPRF does things like this: isolates how fast you turn your head, how quickly your eyes must respond, etc

30
Q

What is the MLF? Why is it important in the pathway to nuclei 3, 4, and 6 and for the coordination of eye movements?

A

MLF is the medial longitudinal fasciculus; it is a crossed fiber tract that carries information from 6 to 3 about which way the eyes should move; it is an ascending tract that input must take from the nucleus of 6 to the nucleus of 3 (eyes)
*this tract only ascends

31
Q

Why do fibers of the MLF cross? Give an example.

A

If you want to look to the left, must excite the left abducens (lateral rectus) and the right occulomotor (medial rectus). Right eye wants to go medial, left eye wants to go lateral, so this crossing over must occur.

32
Q

In the right semicircular canals, if you move your head to the right, which way will the endolymph move? Will this cause excitation or inhibition? Where will this input from the hair cells go?

A

to the left; this will cause excitation on the right because the stereocilia move toward the kinocilium; input will travel to the vestibular ganglion and to the vestibular nuclei

33
Q

If you turn your head to the right, the bone of the semicircular canal will go to the (blank) and the fluid will go to the (blank). Hair cells on the right will be (blank). Vestibular nerve and ganglion excites the vestibular nuclei. What happens to the input on the other side of the head?

A

right; left; excited; inhibition of opposite side

*When exciting one side, you inhibit the other side!!!

34
Q

In the horizontal semicircular canals, fluid movement toward the ampulla is (blank) and movement away from the ampulla is (blank)

A

excitatory; inhibitory

35
Q

What do you use to voluntarily look to the left? What nucleus does this info cross to before traveling to the nucleus for 6, then the MLF, then the nucleus of 3?

A

frontal eye fields; PPRF

36
Q

I want to voluntary look to the left. Explain how I accomplish this.

A

Using my right frontal eye field, I will project to the left PPRF nucleus, then to nucleus of 6, then cross over via MLF, and reach the nucleus of 3. Both eyes will move to the left by firing left nucleus of 6 and right nucleus of 3

37
Q

I turn my head to the right and my eyes move to the left. How does this happen?

A

First, the hair cells in my right vestibular apparatus are excited, while the hair cells in the left side are inhibited. Hair cells on the right will pass this input on to the vestibular ganglion and then to the vestibular nuclei. From there, the input will go the PPRF, then to the nucleus of 6, then will cross over to the MLF nucleus, then will finally reach the nucleus of 3. Both eyes will move to the left.

38
Q

If you damage the left vestibular nucleus, what will happen when you try to look left? What causes the “snap back” that will be observed?

A

This nucleus will not be receiving the drive it needs to move the eye to the left, so the eye will slowly drift to the left, but when it gets all the way over, it will snap back and start again. Snap back is due to cortical input.

39
Q

If you spin to the left, and then stop, in which direction will the snap back (nystagmus) be?

A

to the right

40
Q

Cold water moves the eyes to the (blank) side, while warm water moves the eyes to the (blank) side.

A

opposite; same

41
Q

When you put cold water in someone’s ear, why does this cause opposite nystagmus?

A

Putting cold water in the ear inhibits fibers in that ear, while exciting fibers in the opposite ear. Basically, this mimics turning the head to the opposite side, so the brain thinks that the head is rotating and the eyes will follow to the opposite side.

42
Q

Caloric reflex test:
If the water is cold, relative to body temp, the endolymph falls within the semicircular canal, (blank) the rate of vestibular afferent firing. The eyes then turn toward the ipsilateral ear, with horizontal nystagmus (quick horizontal eye movements) to the (blank) ear

A

decreasing; opposite

43
Q

How can you remember that cold water causes opposite nystagmus, while warm water causes same-side nystagmus?

A

COWS

44
Q

What’s this?

Can be seen clinically in any situation where there is too much drive to the PPRF from the vestibular nuclei on one side

A

nystagmus

45
Q

What is nystagmus

A

When the eyes deviate as far as they can in one direction, they will snap back automatically. If there is continual stimulation of the VOR on one side, the eyes will drift slowly to the opposite side of stimulation and snap back to the same side of stimulation.

46
Q

In a conscious patient, what will happen to the eyes when you irrigate the right ear with cold water?

A

eyes will slowly move to the right, and then snap to the left fast

47
Q

In an unconscious patient with the brainstem intact, what will happen to the eyes when you irrigate the right ear with cold water?

A

the eyes will slowly move to the right, but will not snap back **lose the fast component in unconscious patients

48
Q

In an unconscious patient with a bilateral MLF lesion, what will happen to the eyes when you irrigate the right ear with cold water?

A

MLF lesion will cause you to lose the connection between nucleus of 6 and nucleus of 3, so the right eye will move to the right (laterally - nucleus of 6 intact) but the left eye will stop midway (nucleus of 3 not responsive so unable to medially rotate eye)

49
Q

In an unconscious patient with a low brainstem lesion, what will happen to the eyes upon irrigation of the right ear with cold water?

A

nothing

50
Q

What do MLF lesions lead to?

A

internuclear ophthalmoplesia

51
Q

What is internuclear ophthalmoplesia? What is unique about patients with this problem?

A

nucleus of 3 is unable to fire medial rotation of the eye, so adduction cannot occur
*patients can still look in for accomodation, because this is using a different input (not via PPRF, 6, and 3)

52
Q

What will damage to the abducens nucleus cause?

A

Damage to CN 6 nucleus will kill all neurons going to the lateral rectus muscles, so this will lead to atrophy of the lateral rectus muscle. This is a lower motor neuron lesion. It will also effect neurons going to CN 3 nucleus (which is like an upper motor neuron lesion). So, your medial rectus muscles will still be working, but they are just not getting the drive to fire.

53
Q

If you have damage to CN 6, and not the nucleus of 6, what will happen when you try to look left?

A

You will still have a signal to MLF, so when you try to drive the eyes to the left, the left eye won’t go (lateral rectus out of commission) but the right eye will look left, leading to double vision.

Block 5 Week 2 Meg (10 decks)

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