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N - C > Getting the Balance Right > Flashcards

Getting the Balance Right Flashcards

1
Q

What is the vestibular system?

A

A sensorty system of vital importance in the control of posture and balance.

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2
Q

What is located in the ear that aids the vestibular system?

A

Found in the inner ear, is a series of fluid filled membranous tubes, (LABYRINTHS), which are embedded in the temporal bone.
Labyrinths contain areas of sensory cells, resonsible for detecting TILT OF THE HEAD with respect to the body as well as ANGULAR ACCELERATION.

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3
Q

Describe the sensory cells located in inner ear labyrinths

A

THe sensory cells are hair cells, whose cell bodies are embedded in the bone of the skull.
They have a set of cilia, which protrude into the fluid (endolymph).
The cilia are different; there is a single very large kinocilium and a set of progressively smaller stereocilia.

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4
Q

Describe the APs of sensory hair cells in the vestibular system

A

Distortion of the cilia in the direction of the kinocilium causes depolarisation and increased discharge of APs

Away from the kinocilium leads to hyperpolarisation and decreased discharge of afferents

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5
Q

How is tilt of the head detected?

A

Tilt of the head is detected by macula organs; their cilia are embedded in a blob of jelly which contains crystals of calcium carbonate = otoliths.

These have a greater density than the endolymph and therefore are affected by gravity.

Head tilt, blob distorted -> shearing forces on the cilia

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6
Q

What is a side to side head tilt detected by?

A

Utriculus

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7
Q

What is a forward to bacl head tilt detected by?

A

Sacculus

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8
Q

What are the semi-circular canals (SCCs)?

A

They are like closed tubes of endolymph, they have swellings (ampullae) in which are the cupula organs.

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9
Q

Describe the hair cells in the cupula

A

These hair cells are contained in a gelatinous material, but there are no otoliths.
They detect angular acceleration.

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10
Q

How does the detection of angular acceleration work?

A

If the skull initially at rest is turned, the endolymph at first does not move because of its inertia.
However the base moves instantly because its embedded in the skull.

This produces a shearing force which bend the cilia.

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11
Q

What happens if you are rotating at constant velocity? Is angular momentum detected?

A

If you rotate at constant velocity, the endolymph rotates at the same speed, so no shearing forces
(this takes several seconds after initial acceleration)

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12
Q

If you are rotating at constant velocity what happens in your gelatinous cupluae when you suddenly stop?

A

Endolymph has momentum so doesnt stop moving.

Shearing of cupula in opposite direction to that at the start.

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13
Q

What does cuplula resonse mirror?

A

The acceleration and deceleration phases of movement

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14
Q

How many sets of SCCs are there?

A

3 sets:

  • Posterior = head over heels rotation
  • Anterior = side to side rotation
  • Horizontal = spinning
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15
Q

How does information from SCCs and maculae travel?

A

Pass along the CNVIII (Vestibulocochlear)

Vestibular nerves to the vestibular nuclei and make lots of connections

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16
Q

How do Vestibular nuclei opperate?

A

Vestibular nuclei on one side project to those on the other side of the head

They recieve input from proprioceptors signalling limb and body position, also from neck and eye muscles

Vestibular nuclei project via the thalamus to the cerebral cortex -> perception of movement and body position = KINAESTHESIA

17
Q

There are lots of reflexes mediated via the vestibular system, they involve the vestibulospinal and reticulospinal tracts.
Name them

A
  1. Tonic labyrinthine reflexes
  2. Dynamic righting reflexes
  3. Vestibulo-ocular reflexes
    - Static Reflex
    - Dynamic reflex (vestibular nystagmus)
18
Q

What are the Tonic Labyrinthine Reflexes?

A

Keep the axis of the head in a constant relationship with the rest of the body.

Use information from maculae and neck proprioceptors

19
Q

What are the dynamic righting reflexes?

A

Rapid postural adjustments that are made to stop you falling when you trip.

Long reflexes, involving extension of all limbs
(Cats’ 9 Lives)

20
Q

What are the vestibulo-ocular reflexes?

A

Involve eye movements and the control of the extraocular muscles.

Static reflex and Dynamic reflex.

21
Q

What is the Static Vestibulo-ocular reflex?

A

When you tilt your head, the eyes roll to compensate, so that over a certain range, the image stays the right way up.

Macula input plus proprioceptors from eye muscles -> oculomotor nucleus -> extra ocular nucleus

22
Q

What is the Dynamic Vestibulo-ocular reflex (Vestibular Nystagmus)

A

Vestibular Nystagmus is a series of eye movements that rotate the eye against the direction of rotation of the head and body so that the original direction of gaze is preserved.

23
Q

What are the limitations of eye movement during Vestibular Nystagmus?

A

The extent of the movement is restricted, when eye muscles come to the end of their range of movement, they rapidly flick back to the zero position (i.e. straight ahead)

If rotation continues the slow phase starts again, then flicks back

24
Q

What is the rule for direction of Vetsibular Nystagmus?

A

By convention, direction of nystagmus is the direction of the rapid flick back.

R rotation -> R Nystagmus

25
Q

Nystagmus is used to test vestibular function.

Describe Post-rotatory nystagmus

A

Only carried out in research units.

Subjects are rotated in a Barany chair. If rotate to the left then during acceleration get a left nystagmus.
At the end of rotation, for about 20 seconds, during deceleration get a right nystagmus.

26
Q

Nystagmus is used to test vestibular function.

What is Caloric stimulation?

A

Simple test but only for the horizontal SCC and its associated circuitry.
When the outer ear is washed with either cold or warm fluid, the temperature difference from core (37C), gets through the thin bone and sets up convection currents which effect the endolymph.

Warm fluid (44C) causes nystagmus towards affected side.
Cold (30C) causes nystagmus away from affected side
27
Q

Summarise the results from Caloric stimulation

A

Warm into R ear -> right nystagmus

Cold into R ear -> left nystagmus

28
Q

What other system does the vestibular system work with to control body position?
What is the clinical significance of this?

A

Visual system which is much more dominant

If you want to test vestibular function, need to get rid of visual input.
Patients wear Freznel’s spectacles which prevent visual fixation.

29
Q

Powerful maintained stimilation of the vestibular system can give rise to kinetosis.
What is this?

A

Motion sickness

Most likely to occur if visual and vestibular system inputs to the archicerebellum are in conflict (e.g. if the vestibular system indicates rotation but the visual system does not)

The archicerebellum generated a “sickness signal” to the hypothalamus to bring about the ANS changes.

30
Q

What are the symptoms of kinetosis?

A
  • Nausea and Vomiting
  • Decreased BP and Dizziness
  • Sweating and Pallor
31
Q

How do professionals such as ballerinas who have to spin alot prevent motion sickness?

A

Trained to visually fixate while rotating.

This visual system confirmes the vestibular system and no “sickness signals” sent

32
Q

What is important to remember when irrigating the outer ear?

A

It is important to use fluid of appropriate temperature.

The stimulation of the vestibular system in the absence of movement can cause nausea and vomiting

33
Q

What is Labyrinthitis?

A

Acute interference with normal vestibular function as a result of infection

Post viral common -> all ANS symptoms plus vertigo.

34
Q

What is vertigo?

A

Vertigo is the perception (hallucination) of movement in the absence of movement.

There will also be nystagmus -> Gross impairment of posture and balance, very disabling

35
Q

What is Meniere’s Disease?

A

Vertigo, Nausea, Nystagmus and TINNITUS = subjected noise

Associated with over production of endolymph causing and increase in pressure.
The cause is unknown

36
Q

The inner ear is sensitive to attack by drugs.

Name one

A

Streptomycin

37
Q

If vestibular impairment is chronic, it can be quite well compensated by the visual system.
How is this accomplished?
What are the clinical implications?

A

Learning circuits are set up in the archicerebellum but problems occur if subjects cannot use visual information.

Diving at night should not be done by those without vestibular function, only vision allows them to find the surface so they may swim away from surface and drown

38
Q

What also may cause nystagmus at rest?

A

Lesions of the brain

Can have congenital nystagmus

N - C (35 decks)

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