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Year 2 Term 3 Control > Posture & Balance > Flashcards

Posture & Balance Flashcards

1
Q

Which 3 inputs to the CNS contribute to maintaining balance and posture?

A

1) Vestibular system
2) Visual system
3) Somatosensory system: muscle and joint proprioceptors

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2
Q

In which part of the ear is the vestibular apparatus contained?

A

The inner ear

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3
Q

The vestibular apparatus is a bony labyrinth surrounding a soft membranous labyrinth, what 2 parts can the bony labyrinth be divided into?

A

1) Semicircular canals

2) Vestibule

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4
Q

What are the names of the semi circular canals?

A

Anterior, posterior and lateral

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5
Q

What are the otolith organs and where are they contained?

A

The saccule and the utricle (which the semicircular canals are attached to) contained within the vestibule

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6
Q

What 3 branches is the vestibular branch of CN8 made up of?

A

1) Utricular nerve
2) Saccular nerve
3) Ampullary nerve

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7
Q

In vestibular navigation, how many degrees of freedom are there?

A

6

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8
Q

What are the 3 translational and 3 rotational degrees of freedom?

A 
Translational:
1) X = forward and back
2) Y = left and right
3) Z = up and down 
Rotational:
1) Roll
2) Pitch
3) Yaw
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9
Q

Roll is rotation around what axis?

A

X axis - like tilting head from side to side

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10
Q

Pitch is rotating head around what axis?

A

Y axis - like nodding

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11
Q

Yaw is rotating head around what axis?

A

Z axis - turning face from left to right

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12
Q

Translational motion and linear acceleration are detected by what parts of the vestibular apparatus?

A

The otolith organs - utricle and saccule

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13
Q

Rotational motion and angular acceleration are detected by what parts of the vestibular system?

A

The semi circular canals

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14
Q

The otolith organs detect what kind of acceleration?

A

Linear

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15
Q

The semicircular canals detect what kind of acceleration?

A

Angular

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16
Q

The otolith organs detect what kind of motion?

A

Translational

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17
Q

The semicircular canals detect what kind of motion?

A

Rotational

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18
Q

What are the sensory detects or the utricle and saccule called?

A

Maculae

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19
Q

What are the main structural features of the maculae?

A

1) Matrix of supporting cells surrounding hair cells
2) hair cells possess tufts of cilia that project into the gelatinous calcium carbonate crystals called the otolith membrane

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20
Q

What kind of fibres are the hair cells of the maculae innervated by?

A

Utricular and sacular sensory fibres (go on to form vestibular branch of CN8)

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21
Q

What crystals make up the otolith membrane?

A

Calcium carbonate

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22
Q

What triggers an action potential in the sensory nerve of hair cells?

A

Bending of the cilia and kinocilium

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23
Q

How do movements of hair cells increase or decrease tonic firing of sensory nerve?

A

Movement towards the kinocilium results in depolarisation which increases tonic firing of sensory nerve
Movement away from kinocilium causes hyperpolarisation which decreases tonic firing of sensory nerve

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24
Q

Through what mechanisms does distortion of the cilia and kincilium result in increase in firing of the sensory nerve?

A

1) Stereocilia contain potassium channels
2) Distortion of stereocilia towards the kinocilium results in opening of the K+ channels
3) K+ moves into the hair cells along gradient
4) This K+ movement activates voltage gated calcium channels
5) Influx of calcium causes release of neurotransmitter glutamate, which excites sensory neurones

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25
Q

How does distortion of the cilia and kinocilium result in decreased firing of sensory nerve?

A

1) Stereocilia distorted away from kinocilium

2) This results in closure of potassium channels and hyperpolarisation leading to decreased firing

26
Q

What neurotransmitter is released from hair cells?

A

Glutamate

27
Q

Does endolymph have high or low K+ conc?

A

High K+ conc

28
Q

Kinocilium do not contain voltage gated potassium channels, what is there role?

A

Ensure smooth distortion of cilia

29
Q

Why does tilting of the head result in mechanical distortion of the stereocilia in the of the macula?

A

The calcium carbonate crystals are heavy and move with respect to gravity, distorting the stereocilia which are embedded in the gelatinous membrane

30
Q

What 2 things does the macula provide info about?

A

1) Static equilibrium - position of the head relative to horizontal
2) Dynamic equilibrium (linear acceleration/ deceleration)

31
Q

Maculae in the utricle and saccule are orientated in different planes, which is each orientated in?

A

Utricle - horizontal plane

Saccule - vertical plane

32
Q

How are the hair cells of the macula arranged in terms of direction of depolarisation?

A

One side depolarises in the opposite direction of the other, so for every cell that is depolarised, its opposite is hyperpolarised

33
Q

Why is it important that vestibular nerve axons have a resting discharge (firing) rate?

A

So that hyperpolarisation actually has an effect - ie results in a reduction of firing

34
Q

Where is the main sensory structure of each semi circular canal located?

A

Ampulla

35
Q

Semicircular canals are filled with what fluid?

A

Endolymph

36
Q

The cilia of hair cells located in the ampulla are embedded in what?

A

A gelatinous mass called the cupula

37
Q

What does the cupula do?

A

Forms a barrier for the hair cells against endolymph flow within the canal

38
Q

How basically does head rotation activate the ampullary nerve?

A
  • Due to the inertia of the endolymph (fact it moves slower than the head) the cupula and cilia are distorted by the rotation of the head
  • Physical distortion of the cilia excites/ inhibits the sensory nerve
39
Q

Which way does the cupula bend with respect to the rotation of the head?

A

In the opposite direction

40
Q

What are the 3 functional pairs of the semicircular canals?

A

1) Left and right lateral (horizontal)
2) Left anterior with right posterior
3) Right anterior with left posterior

41
Q

What is the reason for the semicircular canals acting in pairs?

A

Allows for comparison between the 2 with respect to firing of the sensory nerves

42
Q

How does the firing rate of a sensory neurone from a semicircular canal change as the head rotates?

A
  • On initiation of movement the hair cell is depolarised due to inertia of endolymph so get increased firing
  • As endolymph catches up with head movement, the cupula will return to its normal position and get resting rate of firing
  • As the rotation is stopped, due to inertia the endolymph will carry on moving in that direction when the head is stopped resulting in distortion of the cupula in the opposite direction leading to hyperpolarisation which causes decrease in firing
43
Q

During rotation how will the firing of opposite semicircular canals A&B differ?

A
  • Beginning of movement A will be increased (due to depolarisation) and B decreased (due to hyperpolarisation)
  • When endolymph catches up with head movement both will be at resting firing rate
  • When movement is stopped A will be decreased whilst B is increased
44
Q

During rotational movement of the head what does rate of change of firing of sensory neurones correlate with?

A

Rotational/ angular acceleration

45
Q

Afferents from the cupula of semicircular canals project to which nucleus within the brain stem?

A

Medial vestibular nucleus

46
Q

Afferents from the saccule and utricle project to which nucleus of the brain stem?

A

Lateral vestibular nucleus

47
Q

Efferents from the medial vestibular nucleus project to where to do what?

A

The motor neurones of the neck/body trunk to orientate head and stabilise retinal image

48
Q

Efferents from the lateral vestibular nucleus project to where to what?

A

Cerebellum and limb motor neurons to maintain upright body posture

49
Q

What is the role of the vestibule-ocular reflex?

A

Maintenance of vision during head movements

50
Q

Which 2 muscles are involved in the vestibule-ocular reflex?

A

Medial and lateral rectus of the eyes

51
Q

Which 3 cranial nerves are involved in the vestibule-ocular reflex?

A

CN8, 3 and 6

52
Q

How many neurones involved in the vestibule-ocular reflex?

A

3

53
Q

What is the rough arc in the vestibule-ocular reflex?

A

Sensory afferent - semicircular canal to medial vestibular nucleus
Interneuron - from medial vestibular nucleus to oculomotor/abducens nucleus
Motor efferent - CN3/CN4 from nuclei to lateral/medial rectus

54
Q

What is meant by the anticipatory/ feed forward element of postural control?

A

Central command is aware of movement about to occur and causes anticipatory postural adjustment - ie a feedforward mechanism

55
Q

What is the feedback element of postural control?

A

Limb movement can cause postural instability which causes postural adjustment through a feedback mechanism

56
Q

What are the 3 types of postural reflexes?

A

1) Segmental spinal reflexes - influence the posture at multiple levels of spinal cord
2) Automatic righting reflexes which orientate the head with respect to gravity and the body with respect to the head
3) Balance and protective reflexes which regain center of mass over base of support

57
Q

Meniere’s syndrome is a disease that affects the vestibular system, what is it due to?

A

Increased volume of endolymph, rupturing the membranous labyrinth

58
Q

Benign Paroxysmal Positional Vertigo is a disease that affects the vestibular system what is it due to?

A

Calcium carbonate crystals dislodged from otoliths which float into canals and cause movement of the canal which causes illusion of movement

59
Q

Ototxocity can affect the vestibular system how?

A

Drugs or chemicals which usually involve damage of the vestibulocochlear nerve

60
Q

How do vestibular neuritis, brainstem carcinoma, infarction and haemorrhage lead to disruption of postural control?

A

Due to vestibular system damage

61
Q

What is a medulloblastoma, how does this lead to postural instability?

A

Childhood tumour growth within the cerebellum - pt unable to utilize relevant vestibular info from utricles and saccules leading to postural instability

62
Q

How can diseases of the vestibular system lead to dizziness and vomiting?

A

Can give the illusion of movement eg. Menieres and BPPV - which mismatches with the eyes which know you are not moving leading to dizziness and nausea

Year 2 Term 3 Control (11 decks)

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