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MSK > Structure and mechanics of skeletal muscle > Flashcards

Structure and mechanics of skeletal muscle Flashcards

1
Q

What is fasciculation?

A

The normal random twitch of fascicles. Excessive in motor neurone disease.

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2
Q

What are agonists?

A

The prime movers, the main muscle responsible for a particular movement eg biceps brachii

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3
Q

What are antagonists?

A

They oppose prime movers to allow smooth movement, eg triceps

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4
Q

What are synergists?

A

They assist prime movers to neutralise any extra movement and keep the movement in one direction, eg brachialis

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5
Q

What are fixators?

A

They stabilise the action of the prime mover by fixing non-moving joints

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6
Q

What is isotonic contraction?

A

Muscle has constant tension, changes length to move the load eg biceps

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7
Q

What are the two types of isotonic contraction?

A

Concentric- muscle shortens to exert force eg biceps when lifting a load with the arm
Eccentric- muscle extends to exert force eg walking downhill

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8
Q

What is isometric contraction?

A

Muscle is constant length, variable tension eg hand grip when carrying a large suitcase.

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9
Q

Describe Type I muscle fibres

A 
Slow twitch
Red in colour (high mitochondria)
Aerobic resp
High myoglobin
Rich capillary supply
Fatigue resistant
Endurance activities eg posture
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10
Q

Describe Type IIa muscle fibres

A 
Grey/pink colour
Aerobic resp
High myoglobin
Rich capillary supply
Some fatigue resistance
Walking, sprinting
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11
Q

Describe Type IIb muscle fibres

A 
White colour (low mitochondria)
Anaerobic glycolysis
Low myoglobin
Poorer capillary supply
Rapidly fatigued 
Short, intense movements eg weight lifting
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12
Q

What is proprioception?

A

Feedback control of movement.
Proprioreceptors are muscle spindles = specialised fibres that feedback to brain how much tension and stretch there is in the muscle, which allows the brain to know the limb position.

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13
Q

What is a motor unit?

A

A motor neurone and the muscle fibres it innervates. (Can be 3-3000 muscle fibres)

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14
Q

What is crosstalk?

A

Communication between neurones and muscles via signalling molecules, ie atrophy of the nerve leads to atrophy of muscle and vice versa.
Communication is via neurotrophins, cytokines and insulin-like growth factors

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15
Q

How is muscle tone controlled?

A

By motor control centres in the brain via afferent fibre signals from the muscle.
Baseline tone is present in muscle at rest due to motor neurone activity and muscle elasticity.

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16
Q

What is hypotonia and what can it be due to?

A

Low muscle tone due to:
Cerebral or spinal neural shock, lesions of the cerebellum/spinal cord.
Lesion of sensory or lower motor neurones (eg polyneuristis)
Primary degeneration of the muscle (myopathies)

17
Q

How do muscle relaxants work?

A

Inhibit acetylcholinesterase so high ACh level us maintained. Increased initial contraction, but then the sites become blocked and muscle relaxes.

18
Q

What is spatial summation?

A

More motor neurones activated so more muscle fibres are recruited to develop more force.
Controlled by feedback pathway

19
Q

What is temporal summation?

A

Increased frequency of action potentials to muscle fibres.
1 AP leads to a twitch
Infused tetanus needed for continuous muscle force.

20
Q

What are the functions of skeletal muscle?

A

Movement
Stability of joints
Posture
Heat generation

21
Q

How is electromyography used to diagnose motor neurone disease?

A

Electrodes are placed above/in muscles to record electrical activity.
Usually when more force is applied more motor units are recruited but this does not occur in individuals with MND

22
Q

What are the 4 sources of ATP for muscles?

A
  1. Short term stores of ATP in the muscle fibre
  2. Creative phosphate
  3. Glycolysis
  4. Oxidative phosphorylation
23
Q

What is peripheral fatigue?

A

Depletion of muscle glycogen stores, occurs in 1 minute if blood flow interrupted

24
Q

What is intermittent claudication?

A

Intermittent muscle pain, goes away in rest. Caused by reduced blood flow to a muscle eg. due to atherosclerosis

25
Q

What is a muscle contracture?

A

A state of continuous contraction when ATP is depleted, as the myosin heads are unable to detach from the actin filaments.

MSK (8 decks)

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