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Y2 - NMH > Vestibular Systems > Flashcards

Vestibular Systems Flashcards

1
Q

What are the 2 types of head accelerations and what are they detected by?

A
  1. Angular acceleration (head tilt) - detected by the 3-semi-circular canals
  2. Linear acceleration - detected by the 2 otolith organs
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2
Q

The vestibule has vestibulo-ocular, vestibulo-….., vestibulo-….. and vestibulo-….. connections

A

The vestibule has vestibulo-ocular, vestibulo-spinal, vestibulo-autonomic and vestibulo-cortical connections

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3
Q

Give the 7 normal functions of the vestibular system

A
  1. Perception of movement in space and tilt in respect to gravity
  2. Provide reflex balance reactions to sudden instability of gait or posture - ‘vestibulo-spinal reflexes
  3. Stabilise the eyes on earth fixed targets, preserving visual acuity during head movements - ‘vestibular-ocular reflexes’
  4. Assist control of blood pressure and heart rate during rapid up-down tilts - ‘vestibulo-autonomic reflexes’
  5. Assist synchronisation of respiration with body reorientations - ‘vestibulo-autonomic’
  6. Provokes motion sickness when stimulated in unusual motion environments
  7. Provide a reference of absolute motion in space, which together with other senses creates a perception of spatial orientation
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4
Q

List the different vestibular disorders, categorising them by which type of vestibular connections the defects arise from

A
  • Vestibulo-ocular: Unilateral vestibular lesions → Nystagmus, Bilateral vestibular lesions → Oscillopsia during head movements
  • Vestibulo-spinal: Unsteady gait / posture
  • Vestibulo-autonomic: Loss of orthostatic control, if sever can cause severe nausea
  • Vestibulo-cortical - Vertigo - inappropriate perception of presence in space
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5
Q

1) What are the 2 types of vestibular labyrinths?
2) What are they surrounded by (bounded by / located within) and what liquid do they contain?

A

1)

  1. Bony Labyrinth
  2. Membranous Labyrinth

2)

Bony Labyrinth

  • Bounded by petrous temporal bone
  • Filled with perilymph

Membranous Labyrinth

  • Located within the saccule, utricle and semi-circular canals
  • Filled with endolymph
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6
Q

Within the vestibular labyrinth, where are the sensory epithelial cells located?

A
  • Maculae of the utricle and saccule
  • Cristae of ampullae (ampullae are the swollen endings of the semi-circular canals, cristae found within them)
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7
Q

Describe the pathway of the primary afferent neurones from the vestibular labyrinth

A
  • Peripheral processes end in maculae of utricle / saccule and the cristae of the ampullae
  • They have their cell bodies in the vestibular ganglion at the exit of the vestibular labyrinth
  • The fibres terminate as they synapse at the vestibular nuclei in the brainstem
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8
Q

Describe the mechanism of transduction in response to head tilt and acceleration so as to maintain balance in people

A
  • Upon head tilt and acceleration, there is both displacement of endolymph fluid in the semi-circular canals and inertial resistance to acceleration by gravity
  • This causes displacement of the hair cells in the cristae of the ampullae and the maculae of the utricle and saccule, displacement dependent upon direction and acceleration of tilt
  • This causes stereocilia to either bend towards - thus depolarising, or against the kinocilium (main big stereocilia) - thus hyperpolarising the hair cell
  • Thus either increasing or decreasing firing frequency of the vestibular ganglion cell discharge (primary afferent neurone firing)
  • The impulses are eventually sent to the vestibular nuclei in the brainstem which processes this information
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9
Q

What is the kinocilium?

A

The big, main stereocilium of the hair bundle which other stereocilia are attached

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10
Q

What are otoconia?

A

Gelatinous matrix containing calcium carbonate crystals that overlay the otolithic membrane, the stereocilia and hair cells

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11
Q

What are the 2 types of nerve endings on hair cells?

A
  1. Type 1 - chalice-like endings form ribbon synapses
  2. Type 2 - simple nerve terminals
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12
Q

How does the vestibular labyrinth operate when the head is upright, motionless?

A
  • Vestibular ganglion neurons that innervate the saccule have tonic discharge due to constant hair displacement imposed by gravity
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13
Q

What is the cupula?

A
  • Gelatinous projection in which the cilia of the hair cells are embedded
  • Only in the cristae of the ampullae of the semi-circular canals
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14
Q

What are the 2 otolotith organs, what do they detect and, in specific which direction for both?

A
  1. Utricle
  2. Saccule
  • Detect linear acceleration and tilt
  1. Utricle - horizontally
  2. Saccule - vertically
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15
Q

Describe the idea of coordinating bi-directional head movement using the bilateral semi-circular canal activity

A
  • The hair cells in the cristae are unidirectional
  • Head rotation deforms the hair cells of the left and right semicircular canals (in the cristae of the ampullae) in opposite directions
  • Inertia of movement causes endolymph to move in opposite direction with respect to the canals
  • Imagine you rotate head to the left → firing rate of vestibular ganglion cells increases on the left side and decreases on the right side
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16
Q

What is the difference between the static and kinetic labyrinths functionally and anatomically (where are the hair cells located - relevant parts in the ear) ?

A

Static Labyrinth

  • Detects linear acceleration
  • Hair cells in saccule and utricle
  • Saccule - detect upright head due to tonic discharge
  • Utricle - detects linear acceleration

Kinetic Labyrinth

  • Detects angular acceleration
  • Hair cells in semicircular canals
17
Q

1) Where do primary afferent neurones from the static labyrinths terminate (which part of the vestibular nucleus)?
2) Where do primary afferent neurones from the kinetic labyrinths terminate (which part of the vestibular nucleus)?

A

1)

  • Static - lateral and inferior

2)

  • Kinetic - medial and superior
18
Q

Give 4 main targets that vestibular nuclei project to

A
  1. Spinal cord
  2. Nuclei of the extraocular muscles
  3. Cerebellum
  4. Centres for cardiovascular and respiratory control
19
Q

Describe the 2 descending vestibulo-spinal pathways’s routes and their effector functions

A
  1. Lateral vestibulo-spinal tract
  • Descends ipsilaterally in ventral funiculus of spinal cord
  • Terminate in the lateral part of the ventral horn and influence motor neurones to the limb
  • Effector function: influence limb movement, especially extensor muscles
  1. Medial vestibulo-spinal tract
  • Descends bilaterally in medial longitudinal fasciculus (MLF)
  • Terminate in the medial part of the ventral horn and influence motor neurones to neck and back muscles
20
Q

In order to allow the vestibulo-ocular reflexes, which neurones (from where) project to the motor nuclei which in turn innervate the extra-ocular muscles? N.B. on’t need to d?

A
  • Superior vestibular neurones
  • Medial vestibular neurones
21
Q

1) What is the point of the vestibulo-ocular reflex?
2) Describe the mechanisms of how vestibulo-ocular reflexes work in both the horizontal, then vertical directions

A

1)

  • To keep eyes fixated on the target even given the head movements

2)

  • Axons of the medial vestibular nucleus cross the midline and project to the contralateral abducens (VI) nucleus to abduct the eye (in the opposite direction to head rotation)
  • Axons from the VI cross and ascend in the MLF (medial longitudinal fasciculus), and excite the contralateral oculomotor (III) nucleus to adduct the other eye (in the opposite direction to head rotation)
  • Superior vestibular neurones from the vertical canals project ipsilaterally to the 3rd and 4th nuclei to generate vertical vestibular-ocular reflexes
22
Q

How to test for vestibular nystagmus clinically and determin directionality of the nystagmus?

A
  • A horizontal vestibulo-ocular reflex can be elicited by warming or cooling the endolymph in the SCC
  • A warm caloric test applied to the right ear (warm water pumped into right ear) – should produce a slow drift of the eyes away from the stimulated side followed by a fast saccade towards the stimulated side
  • The direction of the nystagmus is named in accordance to the fast saccadic phase
23
Q

Describe the routes of the vestibular afferent pathways to the thalamus and cortex

A
  • All vestibular nuclei project to ventral posterior and ventral lateral nuclei of the thalamus
  • Thalamic nuclei project to two cortical areas (2V and 3a) part of the head region of the primary somatosensory cortex
  • Projection also to superior parietal cortex: ‘vestibular cortex’ concerned with spatial orientation
24
Q

1) What happens in oscillopsia?
2) How to test for it, and the different tests for bilateral oscillopsia and unilateral oscillopsia?

A

1)

  • Impaired vestibulo-ocular reflexes impairs eye stabilisation during rapid head movements, uncomfortable

2)

  • Rapid head movement tests - get the patient to focus sight on a target and move their head
  • Bilateral: continous bilateral head movements - patient fails to adjust eye movements, so you can see multiple saccades to attempt to keep sight fixated on object either side
  • Unilateral: do discrete rapid head movements to one side at a time only. If normal eye adjustments on one side, that side is fine, but if there is failed eye adjustment and there are multiple compensatory saccades for the other side, there is unilateral oscillopsia on this side
25
Q

What deficit can you get with vestibulo-spinal deficits and, what tends to happen if its unilateral?

A
  • Vestibular ataxia
  • If lesion in lateral vestibulo-spinal tract, deficit in limb movement in posture and gait
  • If lesion in medial vestibulo-spinal tract, deficit in head and neck movements in posture and gait
26
Q

What may be affected / what signs and symptoms might you have in vestibulo-autonomic disorders?

A
  • Hypotensive symptoms
  • Dizzy
  • Affects respiratory rhythm
  • In acute unilateral vestibular disorder, you may get motion-sickness like problems
27
Q

1) What is the pathophysiology of BPPV (Benign, Paroxysmal, Positional Vertigo)
2) What makes it worse the characteristic feature of BPPV?

A

1)

  • In the hair cells, there are otolith calcium carbonate crystals
  • OTOCONIAL DEBRIS IN CANALS
  • Bang your head → crystals fall off hair cells and into the fluid in the canals → fluid movement
  • This results in dizziness with head movements – but this is short-lived
  • Debris floating in the canal stimulates the ampulla causing false signals of head rotation - vertigo

2) Provoked by head movement, especially rolling over in bed and tilting the head up or down

28
Q

1) What is the pathophysiology of Meniere’s disease?
2) What is Menieres triad (triad of symptoms)?

A

1)

  • Membrane separating the endolymph of membranous labyrinth and bony labyrinth splits and the fluids mix, causing loss of balance function on affected side
  • Resulting in vicious attack of vertigo and hearing loss (at low frequencies)
  • Build up of endolymphatic pressure (‘hydrops’)

2)

  • Vertigo
  • Tinnitus
  • Deafness
29
Q

Symptoms of vestibular neuritis?

A
  • Vertigo
  • Nausea
  • Unsteadiness
  • Nystagmus
  • Hearing is spared

Y2 - NMH (12 decks)

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