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Neuro > Motor control > Flashcards

Motor control Flashcards

1
Q

Is activation of muscle fibres gradual?

A

No; all or none

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2
Q

how is skeletal muscle attached to bone

A

tendon

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3
Q

describe the structure of skeletal muscle

A

potein filaments make up myofibrils that make up muscle fibres that make up muscle fasiculus which make up muscle

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4
Q

what is a motor unit

A

an alpha motor unit (LMN) and all the extrafusal skeletal muscle fibres it innervates

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5
Q

what is the effect of less fibres innervated by a motor neurone

A

greater variation of movement

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6
Q

what happens when an alpha motor neurone depolarises

A

causes contraction of all fibres in that unit

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7
Q

where are alpha MN that control distal muscles located

A

laterally in spinal cord

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8
Q

where are alpha MN that control proximal muscles located

A

medially in spinal cord

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9
Q

what is the motor plate

A

region of muscle fibre plasma membrane that lies directly under terminal portion of axon

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10
Q

what is a neuromuscular junction

A

junction of an axon terminal with motor end plate

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11
Q

what do stretch receptors do

A

monitor muscle length and rate of change of muscle length

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12
Q

describe the structure of stretch receptors

A

peripheral endings of afferent nerve fibres wrapped around modified muscle fibres - whole apparatus = muscle spindle

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13
Q

what do muscle spindles detect

A

change in muscle resistance to stretch (contraction AND relaxation) regardless of current muscle length

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14
Q

describe the structure of intrafusal fibres;

A

middle 1/3; non, contractile, supplied by fast type 1a afferent sensory nerve
end 2/3s; contractile, gamma MN attached, supplied by slow conducting type 2 afferent

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15
Q

how are muscle spindles attached to extrafusal muscle fibres

A

by connective tissue, in parallel

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16
Q

where are extrafusal fibres found, what do they do and what innervates them

A

skeletal muscle, muscle contraction, alpha MN

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17
Q

where are intrafusal fibres found, what do they do and what innervates them

A

muscle spindle, proprioception, gamma MN

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18
Q

what happens if alpha MN alone is activated

A

increased sensitivity of muscle to stretch

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19
Q

what happens if an alpha AND gamma MN activated

A

prevents central 1/3 of spindle going slack during muscle contraction
- so info about muscle length will be continuously available so can adjust accoridngly

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20
Q

what happens when an external force is applied to an intrafusal fibre

A

pulls on intrafusal, receptor ends activated; the more/ faster muscle is stretched the more receptors fire

21
Q

what happens when an AP arrives at a MN

A

extrafusal contraction so muscle shortens so tension removed from spindle so slows rate of firing of stretch receptor so reduction in sensory information

22
Q

what does tension depend on

A

muscle length
load on muscle
degree of muscle fatigue

23
Q

what do GTO do

A

detect changes in muscle tension

24
Q

where are GTO found

A

junction of skeletal muscle/ tendon

25
Q

what are GTO

A

endings of afferent fibres that wrap around collagen bundles in tendons near their junction with the muscles

26
Q

what are the afferent fibres that lead from GTO to spinal cord

A

1b fibres that run to anterior horn of spinal cord

27
Q

what happens when muscle is stretched/ attached extrafusal muscle fibre contracts (regarding GTO)

A

tension exterted on tendon so straightens the collagen bundle so distorts GTO receptor endings so activating them

28
Q

what do 1b fibres do

A

cause inhibition of a MN of contracting muscle and its synergists

29
Q

why are 1b fibres important

A

regulate muscle tension at normal range and protect it from overload

30
Q

what is the output of GTO

A

proportional to muscle tension

31
Q

are GTO afferent fibres faster or slower than muscle spindles

A

slower

32
Q

what does 1b input do

A

excites alpha MN

33
Q

what does the afferent from GTO do

A

inhibits alpha MN

34
Q

what is muscle tone

A

degree of contraction of muscle/ proportion of Motor units that are active at any time

35
Q

what does high muscle tone look like

A

feels firm/ rigid, resists passive stretch

36
Q

what does low muscle tone look like

A

feels soft/ flaccid, offers little resistance to passive stretch

37
Q

what is the contribution of alpha MN activity in a relaxed person

A

doesn’t make significant contribution to resistance to stretch

38
Q

what is the contribution of alpha MN activity when someone is increasingly alert

A

more activation of alpha MN so muscle tone increases

39
Q

what is hypertonia

A

high muscle tone

40
Q

what causes hypertonia

A

UMN disorder; disorders of descending pathways which normally inhibit MN

41
Q

how can you demonstrate hypertonia and what is seen

A

when joint is moved passively at high speed; increased resistance is due to increased level of alpha MN (LMN) activity which keeps muscle contracted despite attempt to relax it

42
Q

what is spasticity

A

type of hypertonia
muscles don’t develop increased tone until they are stretched a bit, then after a brief increase in tone contraction subsides after a short time

43
Q

what is rigidity

A

type of hypertonia

increased muscle contraction is continual and resistance to passive stretch is constant

44
Q

what is hypotonia

A

low muscle tone accompanied by weakness, atrophy and decreased/ absent reflex response

45
Q

what causes hypotonia

A

LMN lesion, neuromuscular junctions, muscles themselves

commonly accompanies disorders of alpha MN

46
Q

what is clasp-knife phenomenon

A

type of spasticity (hypertonia)
period of ‘give’ occurring after time of resistance - especially when someone bends limb of patient; initially some resistance but after some time resistance falls dramatically

47
Q

what causes clasp-knife phenomenen

A

1b afferent fibres from GTO inhibiting alpha MN once GTO detect tension
- example of inverse stretch (myotatic) reflex

48
Q

when would you expect to see clasp-knife phenomenon

A

UMN lesion

Neuro (11 decks)

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