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MSK Week 1 2017/18 COPY > 3: Muscle Physiology II > Flashcards

3: Muscle Physiology II Flashcards

1
Q

The degree of skeletal muscle tension depends on which two factors?

A

Number of muscle fibres contracting

Tension developed by each individual fibre

which itself depends on summation of contractions and optimal muscle length for contraction

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2
Q

Why do motor units allow the simultaneous contraction of a number of muscle fibres at the same time?

A

Alpha motor neuron is connected to several (hundred?) fibres

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3
Q

Stronger contractions can be achieved by the stimulation of (more / less) motor units.

A

more

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4
Q

During a submaximal contraction, motor unit recruitment is ___ which helps to prevent muscle fatigue.

A

asynchronus

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5
Q

In skeletal muscle, the duration of an action potential is (longer / shorter) than the resulting muscle contraction.

A

shorter

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6
Q

In cardiac muscle, is the duration of the action potential shorter than the resulting contraction?

A

No, longer

Refractory period

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7
Q

If a muscle fibre is restimulated after it has completely relaxed, the second contraction is of (smaller / greater / the same) magnitude compared to the first one.

A

the same

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8
Q

If a muscle fibre is restimulated before it has completely relaxed, the second contraction is added onto the magnitude of the first.

What is this called?

What is the main difference between the first and second contraction?

A

Summation of contractions

2nd contraction is stronger than the 1st

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9
Q

What is tetanus?

Why does it occur?

A

Maximal sustained contraction of muscle

Rapid stimulation, no opportunity to relax

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10
Q

Can cardiac muscle be tetanised?

Why / why not?

A

No

Refractory period

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11
Q

What is a single muscle contraction called?

A

Twitch

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12
Q

What name is given to the “strength” of a muscle contraction?

A

Tension

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13
Q

Every muscle fibre has an optimal ___ which allows it to achieve maximal tension during contraction.

A

length

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14
Q

What is the optimal length of muscle approximately equal to?

A

Its normal resting length

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15
Q

Which structures, attaching skeletal muscle to bone, allow for movement of the skeleton by muscles?

A

Tendons

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16
Q

If skeletal muscle is the contractile component contributing to movement of the skeleton, what type of component is connective tissue and tendons?

A

Elastic component

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17
Q

What are the two types of skeletal muscle contraction?

A

Isotonic contraction

Isometric contraction

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18
Q

What is isotonic contraction?

What is it used for?

A

Muscle tension remains constant

Muscle length changes

Body movements, moving objects

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19
Q

What is isometric contraction?

When is it used?

A

Muscle tension changes

Muscle length stays constant

Supporting objects in place, maintaining posture

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20
Q

Are all skeletal muscle fibres the same?

A

No

21
Q

The main difference between muscle fibres involves the metabolism of which molecule?

A

ATP

22
Q

A motor unit usually contains ___ type of muscle fibre.

A

one

23
Q

Broadly, by which three means can skeletal muscle cells get their hands on ATP for use in contraction?

A

Glycolysis (anaerobically)

Oxidative phosphorylation (aerobic)

Creatine phosphate can give a Pi to ADP > ATP, immediate source but cells have limited supply

24
Q

Why are Type I skeletal muscle fibres known as slow-oxidative fibres?

A

Don’t have a lot of myosin ATPase

Same capacity for oxidative phosphorylation as Type IIa, but less ADP available to them

25
Q

What are Type I fibres also known as?

Are they anaerobic or aerobic?

What sort of activities are they used in?

A

Slow-oxidative or Slow-twitch fibres

Aerobic

Prolonged low intensity work - e.g posture, walking

26
Q

What are Type IIa fibres also known as?

Are they anaerobic or aerobic?

What sort of activities are they used for?

A

Fast oxidative / Intermediate-twitch fibres

Both

Prolonged moderate work e.g jogging

27
Q

What are Type IIx fibres also known as?

Are they anaerobic or aerobic?

What sort of activities are they used for?

A

Fast glycolytic / Fast-twitch fibres

Anaerobic

Short-term, high intensity work e.g jumping, doing a backflip etc.

28
Q

Name two reflexes controlled by motor nerves receiving signals from the brain.

A

Withdrawal reflex

Stretch reflex as in knee jerk etc.

29
Q

What is a reflex?

A

A rapid, predictable response to a specific stimulus

30
Q

Why are testing reflexes important?

A

Allows you to localise lesions in the motor system

31
Q

The stretch reflex is an example of which type of feedback mechanism?

A

Negative feedback

resists increase in muscle length

32
Q

What is the receptor for the stretch reflex?

A

Muscle spindle

no need for a control centre as the reflex is monosynaptic

33
Q

What activates the muscle spindle?

A

Muscle stretch

34
Q

Stretching of the muscle spindle causes which type of neurons to fire?

A

Afferent neurons

35
Q

Where do afferent neurons involved in the stretch reflex synapse?

What do they synapse with?

A

Spinal cord

Alpha motor neuron

36
Q

Alpha motor neurons are (afferent / efferent).

A

efferent

37
Q

What occurs at the end of the stretch reflex, once the efferent alpha motor neuron has been activated?

A

Contraction of stretched muscle

38
Q

How is the stretch reflex elicited?

A

Tapping muscle tendon with a rubber hammer

39
Q

What are muscle spindles also known as?

What are normal muscle fibres known as?

A

Intrafusal fibres

Extrafusal fibres

40
Q

Do muscle spindles contract?

A

Yes, but doesn’t contribute to overall strength (they’re sensory receptors doing their own thing)

41
Q

Where specifically in the muscle are muscle spindles found?

A

Belly

42
Q

How do muscle spindles run compared to normal muscle fibres?

A

Parallel to them

43
Q

What are the sensory nerve endings of muscle spindles called?

A

Annulospiral fibres

44
Q

Muscle spindles have their own (efferent) motor nerve supply.

What are these neurons called?

A

Gamma motor neurons

45
Q

Gamma motor neurons send signals to intrafusal fibres (muscle spindles) telling them to contract - if they don’t contribute to purposeful muscle contraction, why does this happen?

A

So muscle spindles maintain their sensitivity when muscle contracts

46
Q

Pathology of what could cause impairment of skeletal muscle function?

A

1. Intrinsic disease of muscle itself

2. Disease of NMJ

3. Disease of motor neurons supplying the muscle

4. Disease of nerves further up the chain (neurology)

47
Q

What is the general name for disease of muscle?

A

Myopathy

48
Q

What are some common symptoms of muscle disease?

A

Muscle weakness / fatigue

Delayed relaxation

Muscle pain (myalgia)

Muscle stiffness

49
Q

How can neuromuscular disease be investigated?

A

Electromyography (EMG)

Muscle enzymes (e.g creatine kinase)

Inflammatory markers (e.g CRPs, plasma viscosity)

Muscle biopsy

MSK Week 1 2017/18 COPY (10 decks)

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