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MSK > Muscle physiology > Flashcards

Muscle physiology Flashcards

1
Q

Skeletal muscle is innervated by the somatic/autonomic nervous system

A

Somatic

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2
Q

Smooth and cardiac muscle are innervated by the somatic/autonomic nervous system

A

Autonomic

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3
Q

What is a motor unit?

A

One alpha motor neurone and all the muscle fibres it supplies

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4
Q

What is the correlation between precision control and motor unit size?

A

the more precise control the movement requires, the less muscle fibres are involved in the motor unit

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5
Q

Where has the largest ratio of neurones to muscle fibres in a motor unit in the human body?

A

The extraoccular muscles
Neurones:fibres = 1:3
Contrast with gastrocnemius
neurones:fibres = 1:1000-2000

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6
Q

What is the correlation between strength of muscle and motor unit size?

A

the more power (with less precision) required, the more muscle fibres are supplied by a single neurone.

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7
Q

Each muscle fibre is formed from many cells - true/false

A

False - each muscle fibre is a single cell

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8
Q

Each muscle fibre is formed from myofibrils - true/false

A

True

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9
Q

Myofibrils are the smallest contractile unit of a muscle - true/false

A

False

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10
Q

Sarcomeres are the smallest functional contractile units of skeletal muscle - true/false

A

True

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11
Q

Skeletal muscle usually attaches to the skeleton via _____ to give a lever system

A

Tendons

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12
Q

A myofibril contains alternating bands of thick ______ filaments and thin ______ filaments

A

Myosin

Actin

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13
Q

The A-band contains many/few myosin filaments with many/few actin filament

A

Many

Few

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14
Q

The H-zone is a region within the _____ ______ that appears slightly lighter

A

A-band

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15
Q

The H-zone contains only myosin/actin filaments

A

Myosin

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16
Q

The I-band consists of thin actin filaments and/without thick myosin filaments

A

Without thick filaments

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17
Q

The H-zone shortens in contraction, the A-zone remains the same/shortens and the I-zone stays the same - true/false

A 
False
H-zone shortens
A-zone remains the same
I-zone shortens 
Entire sarcomere shortens
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18
Q

ATP is required for both contraction and relaxation of smooth muscle. True/False

A

True

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19
Q

Ca2+ ions are required to allow ATP to bind to myosin heads. True/false

A

False - Ca2+ is required to allow cross bridge formation

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20
Q

How does Ca2+ affect muscle contraction

A

Ca2+ affects muscle contraction as it displaces the troponin-tropomyosin complex and exposes the myosin cross-bridge binding sites on the actin filaments

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21
Q

What are the two factors affecting the production of tension in a muscle?

A

Number of muscle fibres contracting

tension developed by each contracting fibre

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22
Q

In skeletal muscle the duration of the AP is much shorter/longer than the twitch.

A

Shorter

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23
Q

A shorter AP than a twitch means that your muscles can repeatedly contract to give the same amount of force. True/false

A

False - muscle repeatedly contracting gives an increased force - summation of twitches

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24
Q

What is tetanus?

A

Tetanus is when the muscle fibres are repeatedly stimulated to contract with no relaxation between stimuli and a maximum sustained contraction is generated

25
Q

Cardiac muscle cannot be tetanized. True/false

A

true

26
Q

Why can cardiac muscle not be tetanized?

A

Its relatively long refractory period prevents overstimulation

27
Q

Tension within a contracting muscle increases/decreases with increasing frequency of the muscle stimulation

A

Tension within a contracting muscle increases with increasing frequency of the muscle stimulation

28
Q

Give the relationship between length of fibre and contraction tension

A

Maximum contraction is achieved when the muscle fibre is at its optimum length before onset of contraction

29
Q

Why does optimal length give maximum contraction?

A

the optimal length is the point at which the most actin binding sites and myosin cross bridges overlap.

30
Q

How does a stretched fibre affect the strength of the contraction?

A

There is less/insufficient overlap of actin binding sites and myosin cross bridges and so contraction is less/doesnt occur

31
Q

How does a shortened fibre affect the strength of the contraction?

A

there is plenty of overlap but the muscle cannot shorten much further and so contraction is decreased

32
Q

In the body a resting muscle is approximately its optimal length - true/false

A

True

33
Q

Skeletal muscle tension, resulting from cross bridge cycling, is transferred to bone via dilation and relaxation of tendons and muscle connective tissues - true/false

A

False - transferred via the stretching and tightening of connective tissues and tendons

34
Q

There are two types of muscle contraction - name them

A

Isotonic and isometric

35
Q

What is isotonic contraction?

A

Contraction where muscle tension remains constant but muscle length changes

36
Q

What is isometric contraction?

A

Muscle tension develops across the muscle but fibre length remains constant.

37
Q

Give TWO examples of when an isotonic contraction is used

A

(1) For body movements

(2) for moving objects

38
Q

Give TWO examples of when an isometric contraction is used

A

(1) supporting objects in a fixed position

(2) maintaining body posture e.g. while walking

39
Q

What is the relationship between load and the velocity at which muscles shorten?

A

the bigger the load, the slower the muscle shortens

40
Q

What is a congenital myopathy?

A

A condition, present at birth, which shows microscopic histological changes leading to reduced contractility of muscles

41
Q

Apart from congenital myopathy, name three (of four) other causes of intrinsic muscle diseases

A

Acquired myopathy e.g. polymyositis
Endocrine myopathy e.g. Cushing’s Syndrome, thyroid disease
Toxic myopathy e.g. from alcohol or statins
Chronic degeneration of contractile elements e.g. Muscular dystrophy

42
Q

What is a reflex?

A

A stereotyped response to a specific stimulus

43
Q

What is the simplest form of co-ordinated movement?

A

A reflex

44
Q

Why are the neural pathways of reflexes important?

A

They allow for localising lesions in the motor system.

45
Q

Where are pathways responsible for reflexes located?

A

At various levels along the motor system

46
Q

What is the simplest example of a monosynaptic spinal reflex?

A

The stretch reflex.

47
Q

Stretch reflexes are a positive feedback mechanism by which the muscle resists the passive change in muscle length to maintain optimum length - true/false

A

False - stretch reflex is a NEGATIVE feedback mechanism by which the muscle resists the passive change in muscle length to maintain optimal length.

48
Q

The stretch reflex helps to maintain posture while standing/walking (choose one)

A

Walking

49
Q

The sensory receptor in the stretch reflex is ________ activated by ________

A

The sensory receptor in the stretch reflex is muscle spindle activated by muscle stretch

50
Q

Stretching the muscle increases/decreases firing in the afferent/efferent neurones.

A

Increases and afferent

51
Q

Afferent neurones in the stretch reflex synapse in the ____ ____ with alpha/beta/gamma ______ neurones.

A

Afferent neurones in the stretch reflex synapse in the Spinal cord with alpha/beta/gamma motor neurones.

52
Q

Activation of the stretch reflex results in contraction/relaxation of the stretched muscle

A

Contraction

53
Q

In the stretch reflex, contraction/relaxation of antagonist muscles happens simultaneously with contraction/relaxation of the stretched muscle

A

relaxation of the antagonist

Contraction of the stretched muscle

54
Q

Fibres in muscle spindles are known as extrafusal/intrafusal fibres. Fibres not part of muscle spindles are known as extrafusal/intrafusal fibres

A

Intrafusal fibres - muscle spindle

Extrafusal fibres - not muscle spindles

55
Q

Muscle spindles are found within the ________ of the muscle and run parallel/anti-parallel/perpendicular to the muscle fibres

A

Within the belly of the muscle and run parallel to the muscle fibres

56
Q

Muscle spindles have sensory nerve endings known as ________

A

Annulospiral fibres

57
Q

Discharge from annulospiral fibres decreases when muscle is stretched - true/false

A

False - discharge from annulospiral fibres increases when muscle is stretched.

58
Q

the afferent/efferent neurone supplying the muscle spindle is the alpha/beta/gamma motor neurone

A

efferent - gamma neurone

59
Q

What is the function of the gamma motor neurone?

A

It adjusts the tension in the spindle to maintain sensitivity to stretch when the muscle is contracting.

MSK (7 decks)

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