Physiology of skeletal muscle contraction Flashcards Preview

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Flashcards in Physiology of skeletal muscle contraction Deck (94):
1

What binds to troponin C in skeletal muscles?

4 Ca2+

2

What binds to troponin C in the heart muscle?

3 Ca2+

3

What happens to troponin after calcium binds?

Changes conformation

4

What does a conformational change in troponin (TnC) lead to?

Shuts off TnI
tropomyosin-troponin leaves F-actin groove
Unmasks the myosin binding site on actin

5

What happens to the next myosin that binds?

Next myosin head makes cross bridges (cycling) to actin
Myosin breaks down ATP
Myosin pulls thin filaments

6

What is total TnI used as a marker of?

Total muscle breakdown

7

What is cardiac TnI used as a marker of?

Myocardial infarction

8

What is cross bridge cycling?

Molecular cycle of actin-myosin interaction
Mechanism of contraction at a molecular level

9

What does contraction through cross bridge cycling depend on?

Binding of myosin heads to thin filaments (actin) at specific binding sites

10

Describe the resting state of a sarcomere

Myosin heads are blocked from binding to actin by tropomyosin, which occupies the specific binding sites ( F actin double helical groove)

11

What can increase the force generated?

Increased overlap of thick and thin filaments

12

When does the greatest force generation occur?

When sarcomere is at optimal length

13

Describe the process of cross bridge cycling in terms of te 4 reactions

Myosin releases actin
Myosin head cleaves ATP
Myosin binds actin
Power stroke

14

Where is creatine found?

Muscle fibres

15

What is creatine phosphorylated to?

Creatine phosphate

16

How is energy stored in muscle?

Stored as creatine phosphate in muscle fibres

17

Describe what happens to ATP during cross bridge cycling

ATP is hydrolysed to ADP + Pi , creatine phosphate donates high energy phosphate to ADP restoring it to ATP

18

How are ATP levels in muscle kept stable?

Buffering and regeneration

19

Which enzyme catalyses the reaction of ATP during cross bridge cycling?

Creatine kinase or Creatine phosphokinase (CK, CPK) in both directions

20

What is creatine?

Small molecule that accepts high energy phosphate bonds from ATP

21

What is plasma creatine phosphokinase a marker of?

Muscle destruction

22

What is creatinine a diagnostic marker of?

Kidney function

23

What is creatinine?

Breakdown product of creatine

24

What are the two calcium gradients?

Extracellular vs cytosolic free calcium
SR vs cytosolic free calcium

25

What provides most of the calcium?

Efflux of calcium from the sarcoplasmic reticulum to cytoplasm

26

What does calcium entering the cell from the outside provide?

Only a small fraction of the calcium needed for muscle contraction

27

What does calcium trigger?

Contraction

28

Which neurotransmitter leads to depolarisation?

ACh

29

What does depolarisation cause?

Increase in calcium

30

Name the receptor where there is a net inward current

Active nicotinic AChR

31

How does depolarisation spread?

Through T tubules

32

What do local action potentials trigger?

Ca2+ efflux from terminal cisternae across sarcoplasmic reticulum into the fibre cytoplasm

33

Where is the ryanodine receptor found?

In the sarcoplasmic reticulum

34

What does the ryanodine receptor do?

Releases Ca2+ from SR

35

What is the ryanodine receptor triggered by?

Voltage sensor on Ca2+ channel

36

Where is SERCA found?

In sarcoplasmic reticulum

37

What does SERCA stand for?

Smooth endoplasmic reticulum calcium ATPase

38

What is the function of SERCA?

Pumps Ca2+ back into SR

39

What does SERCA require?

ATP

40

What causes a twitch?

Single action potential leading to calcium release from sarcoplasmic reticulum

41

What causes a twitch to end?

Ca2+ ions are rapidly pumped back into the SR

42

Describe the molecular basis of tetany

Frequent APs
Insufficient Ca2+ resequestration
Summation of contraction

43

Name the two types of muscle fibres

Slow twitch
Fast twitch

44

Describe the structure of slow twitch fibres

High myoglobin
Many mitochondria

45

Give the size, colour and property of slow twitch fibres

Red
Small diameter
Oxidative

46

Give the size, colour and property of fast twitch fibres

White
Large diameter
Non-oxidative

47

How do the two muscle fibre types differ?

Aerobic (slow fibres) vs anaerobic respiration
Faster calcium reuptake in fast fibres
Maximum tension produced in fast fibres
Fatigue resistance in slow fibres

48

Name the fibre types in order of slow to fast fibres

Type 1
Type IIA
Type IIX
Type IIB

49

What do muscles contain?

A mixture of fibre types

50

What does muscle composition depend on?

Muscle action

51

Give the composition of soleus

80% Type 1 (slow)
20% Type IIA

52

Give the composition of vastus lateralis

Mixture of type 1, IIA, IIX

53

Name the different groups of physical fitness

Inactive
Moderately active
Endurance athlete
Anaerobic athlete

54

What colour do type 1 fibres stain?

Dark

55

What colour do type II fibres stain?

Light

56

List the 3 types of coordination of contraction

Motor units
Tetany
Fusion of myocytes into long myofibres

57

Define motor unit

A single alpha motor neuron and all muscle fibres that it innervates

58

What do motor units function as?

A single contractile unit of skeletal muscle

59

What type are all muscle fibres in a single motor unit?

The same

60

Describe the synapses in large muscles responsible for powerful gross contractions

Single motor neuron may synapse on 1000 fibres

61

Describe the synapses in small muscles mediating precision movements

Single motor neuron may synapse with as few as 2 - 3 fibres

62

What determines the muscle fibre?

Type and function of lower motor neuron

63

Define isometric contraction

Generates a variable force while length of the muscle remains unchanged

64

Define isotonic contraction

Generates a constant force while the length of the muscle changes

65

Describe the types of force generation when picking up a glass

stage 1: isometric – force increases, joint does not move
Muscle Force < force of gravity –> force increases
biceps and brachioradialis generate force by isometric contraction as muscles have not yet shortened

stage 2: isotonic – force remains the same, arm moves
Glass moves upward in response to force
an isotonic contraction starts as the force generated by the muscles overcomes gravitational and inertial forces keeping glass on the table

glass starts to rise as the muscles shorten and the elbow bends and force generated by the muscle is constant as the glass is moving

66

What does muscle contraction not necessarily mean?

Muscle shortening

67

What is meant by concentric?

Force during contraction

68

Give an example of concentric force

Tossing a ball into the air

69

What is meant by eccentric?

Force during muscle elongation

70

Give an example of eccentric force

When braking
When the weight of the object is overwhelming - catching a ball

71

When can both types of force occur?

In one behaviour

72

What does proprioception control?

Force generation

73

What is proprioception based on?

Length and strength

74

Describe the size principle

As the initial isometric contraction occurs more and more motor units are recruited starting with smaller ones and progressively adding larger ones

Allows fine gradation of force for small movements

75

What does lower motor neuron disease cause?

Weakness
Muscle atrophy

76

What does upper motor neuron disease cause?

Spasticity, hypertonia

77

Describe the stretch reflex

Controls muscle length
Increases muscle force

78

What is westphal's sign?

Lack of patellar reflex

79

What is the function of the patellar reflex

Posture and balance

80

Name the fibres for sensation in the stretch reflex

Intrafusal fibres

81

Name the fibres for contraction in the stretch reflex

Extrafusal fibres

82

What does the muscle spindle fibre do?

Detects stretch

83

Give the location of the muscle spindle

Parallel to muscle fibres

84

What do the muscle spindles contain?

3-12 intrafusal fibres

85

What do gamma motor neurons do?

Increase sensitivity
Drive contraction of edge of intrafusal fibres

86

What are sensors from muscle spindles called?

Type 1a and Type 2

87

Where are sensors from muscle spindles found?

Wrap around the intrafusal fibres

88

What do sensors from muscle spindles do?

Detect stretch of central non-contacting region using stretch receptors

89

What is the function of the muscle spindle?

Like a thermostat that regulates the relationship between the muscle length and muscle contractility
ie. the relationship between neural drive and force generation

90

What can absence of the muscle spindle reflex suggest?

Receptor damage
Femoral nerve damage
Peripheral nerve disease eg. peripheral neuropathy

91

What can happen to the muscle spindle reflex in upper motor neuron disease

Can lead to hypertonia and spasticity
UMN inhibits normal descending inhibitory input to spinal interneurons
Spindle reflex can become over sensitive - can attempt to contract the muscle all the time

92

What is the function of the tendon reflex?

Protects from overloading
Decreases muscle force- dropping the load - sensor firing - decreased contraction

93

Describe the path of the tendon reflex

Sensor to spinal cord
Interneuron to motor neuron
Motor neuron inhibited
Motor neuron to muscle

94

What is the sensor of the tendon reflex?

Golgi tendon organ - detects tension
in series with muscle
in tendon - near border of muscle