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MODULE 8 - Neurology > FUNCTIONAL ANATOMY - Vestibular System > Flashcards

FUNCTIONAL ANATOMY - Vestibular System Flashcards

1
Q

What is the vestibular system?

A

The primary sensory system which maintains balance

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2
Q

What are the three structures within the inner ear which contribute to the vestibular apparatus?

A

Semicircular ducts
Utriculus
Sacculus

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3
Q

What is the function of the semicircular ducts in the vestibular system?

A

Sensory detection of rotary acceleration and declaration of the head

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4
Q

What is the name of the neuroepithelium of the semicircular ducts?

A

Crista ampullaris

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5
Q

Where in the semicircular ducts is the crista ampullaris located?

A

The crista ampullaris is located in the ampullae

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6
Q

Describe the structure of the crista ampullaries

A

The crista ampullaris has mechanoreceptors known as hair cells which have sterocilia projecting into the overlaying gelatinous cupula. These hair cells are innervated by the vestibular branch of CN VIII

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7
Q

Describe briefly how the semicircular ducts detect rotary acceleration and deceleration of the head

A

Rotation of the head will cause the endolymph within the semicircular ducts to move in the opposite direction to the initial movement, causing deflection of the cupula and subsequent deflection of the stereocilia of the hair cells, triggering depolarisation of the vestibular branch of CN VIII to increase action potential frequency on that side of the head and hyperpolarisation of the vestibular branch of CN VIII on the other side of the head to decrease action potential frequency

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8
Q

How does the arrangement of the semicircular ducts allow for the detection of head rotation in any direction?

A

The semicircular ducts are orientated roughly 90° from each other to maximise the ability to detect rotation of the head

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9
Q

What is the function of the utriculus and the sacculus in the vestibular system?

A

Sensory detection of horizontal and vertical linear acceleration and deceleration of the head

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10
Q

What is the name of the neuroepithelium in the utriculus and the sacculus?

A

Macula

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11
Q

Describe the structure of the macula

A

The macula has mechanoreceptors known as hair cells with sterocilia which project into the overlying gelatinous otolithic membrane with otolith crystals on the surface. These hair cells are innervated by the vestibular branch of CN VIII

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12
Q

How do the hair cells within the utriculus and sacculus exhibit topographical organisation?

A

Groups of hair cells within the utriculus and sacculus are sensitive to movement in specific directions

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13
Q

Describe how the utriculus and sacculus detect linear acceleration and deceleration of the head

A

When the head undergoes linear acceleration or deceleration, the otolith crystals will pull the otolithic membrane and subsequently the stereocilia in the opposite direction of the initial movement, stimulating depolarisation and increase action potential frequency in the vestibular neurones innervating the hair cells sensitive to that specific direction, and hyperpolarisation to decrease action potential frequency of the vestibular neurones innervating the hair cells that are not sensitive to that specific direction

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14
Q

Why are the hair cells in the utriculus more sensitive to horizontal linear movement?

A

The macula is orientated horizontally in the utriculus so the hair cells are more sensitive to horizontal linear movement

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15
Q

Why are the hair cells in the sacculus more sensitive to vertical linear movement?

A

The macula is orientated vertically in the sacculus so the hair cells are more sensitive to vertical linear movement

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16
Q

Which structures receive sensory information from the vestibular apparatus via the vestibular neurones of cranial nerve VIII?

A

Vestibular nuclei in the brainstem

17
Q

What are the four vestibular nuclei?

A

Rostral vestibular nucleus
Caudal vestibular nucleus
Medial vestibular nucleus
Lateral vestibular nucleus

18
Q

Which three structures receive efferent fibres from the vestibular nuclei?

A

Brainstem
Cerebellum
Spinal cord

19
Q

Which two vestibular nuclei send efferent fibres to the brainstem?

A

Lateral vestibular nucleus
Medial vestibular nucleus

20
Q

Which cranial nerve nuclei in the brainstem receive projections from the vestibular nuclei?

A

CN III (oculomotor) nucleus
CN VI (abducens) nucleus

21
Q

What is the vestibulo-ocular reflex?

A

The vestibulo-ocular reflex is the compensatory movement of the eye in the opposite direction to initial head rotation to maintain the visual field in the centre of the retina

22
Q

Describe the vestibulo-ocular reflex

A

Rotation of the head will cause depolarisation of the ipsilateral vestibular branch of CN VIII which will project to the ipsilateral vestibular nuclei at the brainstem. The vestibular nuclei will project to the contralateral CN VI (abducens) nucleus, stimulating the contraction of the contralateral lateral rectus extraocular muscle. The vestibular nuclei will also project to the ipsilateral CN III (oculomotor) nucleus, stimulating contraction of the ipsilateral medial rectus muscle

23
Q

What is the function of the cerebellum in the vestibular system?

A

The cerebellum coordinates the position of the trunk, limbs and neck in relation to the position of the head

24
Q

Which two vestibular nuclei send efferent fibres to the spinal cord?

A

Lateral vestibular nucleus
Medial vestibular nucleus

25
Q

What is the function of the efferent fibres of the lateral vestibular nucleus projecting to the spinal cord?

A

Lateral vestibular nuclei have efferent projections to the cervical and lumbar regions of the spinal cord to adjust body posture

26
Q

What is the function of the efferent fibres of the medial vestibular nucleus in relation to the spinal cord?

A

Medial vestibular nuclei have efferent projections to the cervical region of the spinal cord to adjust head and neck posture

27
Q

What is postural equilibrium?

A

Regulation of posture with respect to gravity

28
Q

What is static equilibrium?

A

Maintaining balance whilst the body is in a stationary position

29
Q

What is dynamic equilibrium?

A

Maintaining balance whilst the body is in motion

30
Q

What are the two forms of control involved in maintaining posture?

A

Feedback control
Feedforward control

31
Q

What is feedback control?

A

Continuous monitoring and adjusting of the body based on sensory information

32
Q

What is feedforward control?

A

Anticipating and preparing for movements or postural changes before they happen

33
Q

What stimulates the vestibular reflexes?

A

Vestibular reflexes are stimulated by the movement of the head relative to the vertical axis

34
Q

What stimulates the tonic neck reflexes?

A

Tonic neck reflexes are stimulated by the movement of the head relative to the rest of the body

35
Q

What is the labyrinthine righting reflex?

A

The labyrinthine righting reflex restores normal posture in an animal that has fallen or is unbalanced

36
Q

Which four components are required for the labyrinthine righting reflex?

A

Utriculus
Saculus
Semicircular ducts
Muscle spindles in the neck

37
Q

Describe briefly the labyrinthine righting reflex in cats

A

The head is initially adjusted relative to the field of gravity followed by the extension of the legs to prepare the cat for landing

MODULE 8 - Neurology (27 decks)

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