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Module 204 MSK & Immune system > T2 L5 Physiology of skeletal muscle contraction > Flashcards

T2 L5 Physiology of skeletal muscle contraction Flashcards

1
Q

How many thin filaments are adjacent to 1 thick filament?

A

6

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2
Q

How many thick filaments are adjacent to 1 thin filament?

A

3

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3
Q

In the sarcomere, which bands become shorter during contraction?

A

H and I

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4
Q

What 3 proteins are on thin filaments?

A

F actin
Tropomyosin
Troponin

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5
Q

What ions travel across membrane during skeletal action potential?

A

Na+ goes in during depolarisation
k+ goes out during repolarisation
Ca2+ goes in during depolarisation

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6
Q

What process connects action potential to muscle contraction?

A

Excitation-contraction coupling

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7
Q

What microscopic structures anchor the thick and thin filaments?

A

Thick filaments are anchored by M band (minor proteins of thick filament)
Thin filaments are anchored to Z disc

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8
Q

What happens when calcium binds to troponin C?

A

Troponin C changes conformation which shuts off troponin I. Tropomyosin-troponin leaves F-actin groove which unmasks myosin binding site on actin

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9
Q

What is troponin C?

A

Calcium binding

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10
Q

What is troponin I?

A

Inhibitory

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11
Q

What is the marker for muscle breakdown?

A

Total troponin I

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12
Q

What is the marker for myocardial infarct?

A

Cardiac troponin I

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13
Q

What is cross-bridge cycling?

A

Molecular cycle of actin-myosin interaction

Mechanism of control at molecular level

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14
Q

What is F-actin?

A

Filamentous actin

Long polymer chain of actin

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15
Q

What is G-actin?

A

Globular actin

Single subunit

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16
Q

What are the 4 steps of cross bridge cycling?

A

1) Myosin releases actin
2) Myosin head cleaves ATP
3) Myosin binds actin
4) Power stroke

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17
Q

What is the effect of increased overlap of thin and thick filaments?

A

Increased force

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18
Q

Describe the creatine found in muscle fibres

A

Small, organic, nitrogen-containing molecule

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19
Q

What happens when creatine accepts high energy phosphate bonds from ATP?

A

Phosphorylated to creatine phosphate which stores energy in muscle

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20
Q

Why can’t energy be stored as excess ATP?

A

The ATP levels must be kept stable

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21
Q

What is creatine phosphokinase?

A

Also known as creatine kinase
Enzyme that adds a phosphate to creatine
Plasma marker of muscle destruction
Large molecule detected by antibodies

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22
Q

What is creatinine?

A

Breakdown of creatine - marker of kidney function

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23
Q

What are the 2 calcium gradients involved in contraction?

A

Extracellular vs cytosolic free Ca2+

Sarcoplasmic reticulum vs cytosolic free Ca2+

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24
Q

What is excitation contraction (EC) coupling?

A

Molecular mechanism for how depolarisation of plasma membrane leads to release of Ca2+ into cytoplasm following contraction

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25
Q

Describe the ryanodine receptor (RyR)

A

In sarcoplasmic reticulum membrane
Releases calcium from sarcoplasmic reticulum
RyR channels in terminal cistern of SR are in contact with L-type calcium channels in T-tubule membranes

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26
Q

What triggers the release of calcium through RyR?

A

Voltage sensor on Ca2+ channel

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27
Q

Describe SERCA

A

Smooth endoplasmic reticulum calcium ATPase
In SR membrane
Pumps Ca2+ back into sarcoplasmic reticulum using ATP

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28
Q

Describe L-type calcium channels

A

Most common calcium selective channel
Voltage gated so opens when cell is depolarised
In plasma membrane

29
Q

Describe how tetany occurs

A

Single AP –> sufficient Ca2+ released from SR –> twitch
Ca2+ pumped back into SR –> end of twitch
Frequent APs –> time interval between APs is shortened –> insufficient Ca2+ re-sequestered –> summation of contraction

30
Q

What are the 2 main types of muscle fibres?

A

Slow twitch - type 1

Fast twitch - type 2

31
Q

Describe slow twitch fibres

A

Red, oxidative, small diameter
High myoglobin
Many mitochondria
Postural or weight bearing muscles

32
Q

Describe fast twitch fibres

A

White, non oxidative, wide diameter
Lower myoglobin
Increased energy from glycolysis

33
Q

What are the differences between the muscle fibre types?

A

Aerobic (slow), anaerobic (fast)
Faster calcium re-uptake in fast twitch
Maximum tension produced in fast twitch
Fatigue resistance in slow twitch

34
Q

What does the fibre type distribution depend on?

A

Muscle action

35
Q

Describe the fibre type distribution in soleus muscle

A

80% type I (slow)

20% type IIA

36
Q

Describe the fibre type distribution in vastus lateralis

A

Mixture of type I, IIA, IIX

37
Q

Describe the characteristics of type I fibres

A 
Sub-name: slow-oxidative
ATP generation: aerobic
Contraction rate: slow
Fatigue resistance: high
Fibre diameter: small
Myoglobin: high
Mitochondria: many
Capillaries: many
Fuel for storage: triglycerides
38
Q

Describe the characteristics of type IIA

A 
Sub-name: fast oxidative-glyoclytic
ATP generation: aerobic / anaerobic
Contraction rate: fast
Fatigue resistance: intermediate
Fibre diameter: intermediate
Myoglobin: high
Mitochondria: many
Capillaries: many
Fuel for storage: creatine phosphate, glycogen
39
Q

Describe the characteristics of type IIB (IIX) fibres

A 
Sub-name: fast, glycolytic
ATP generation: anaerobic
Contraction rate: fastest
Fatigue resistance: low
Fibre diameter: high
Myoglobin: low 
Mitochondria: few
Capillaries: few
Fuel for storage: creatine phosphate, glycogen
40
Q

What are the 3 types of coordination?

A

Motor units
Tetany
Fusion of myocytes into long myofibres

41
Q

What is a motor unit?

A

Single alpha motor neuron and all the muscle fibres it innervates

42
Q

How many motor units in a peripheral muscle?

A

100-500

43
Q

How many muscle fibres per motor unit in a biceps branch?

A

500

44
Q

How many muscle fibres per motor unit in gastrocnemius?

A

2000

45
Q

What is the percentage of slow twitch in gastrocnemius in sprinters?

A

25%

46
Q

What is the percentage of slow twitch in gastrocnemius in marathoners?

A

93-99%

47
Q

How many muscle fibres per motor unit in extrinsic eye muscles?

A

9

48
Q

What determines the muscle fibre?

A

Type and function of lower motor neuron

49
Q

What is isometric?

A

Generates variable force while length of muscle remains unchanged

50
Q

What is isotonic?

A

Generates constant force while length of muscle changes

51
Q

Describe the steps for picking up a glass

A

Stage 1 - isometric

  • force increases, joint doesn’t move
  • muscle force < force of gravity –> force increases
  • biceps and brachioradialis generate force by isometric contractions as muscles haven’t yet shortened

Stage 2 - isotonic

  • force remains same, arm moves
  • glass moves upward in response to force
  • isotonic contraction starts as force generated by muscle exceeds gravitational and inertial forces keeping glass on table
52
Q

What is concentric?

A

Force during contraction e.g. tossing a ball into air

53
Q

What is eccentric?

A

negatives
Force during muscle elongation
Eg when braking or when weight of object is overwhelming such as when catching a ball

54
Q

Describe the recruitment size principle

A

As initial isometric contraction occurs:

  • more motor units are recruited (start with smaller ones and progressively add larger ones)
  • allows fine gradation of force for small movements
55
Q

Describe lower motor neurons

A

Signal starts in spinal cord and extends to effector muscles in periphery

56
Q

Describe the signs of lower motor neuron disease

A

Weakness

Muscle atrophy

57
Q

Describe upper motor neurons

A

Signal starts in brain and extends to spinal cord to synapse with lower motor neuron

58
Q

Describe upper motor neuron disease

A

Inhibits normal inhibitory input to spinal interneurons

Spindle becomes oversensitive and attempts to contract muscle all the time

59
Q

What are the signs of upper motor neuron disease?

A

Spasticity

hypertonia

60
Q

What does the stretch reflex do?

A

Controls muscle length

Increases muscle force

61
Q

What is Westphal’s sign and what causes it?

A 
Lack of patellar reflex
Damage to:
- femoral nerve
- receptor damage
- peripheral nerve disease e.g. peripheral neuropathy
-cerebellar damage
62
Q

Describe sensory intrafusal fibres

A

Skeletal muscle fibres that serve as specialised sensory organs (proprioceptors) that detect amount and rate of change in length of muscle
Constitute muscle spindle and don’t generate contractile force associated with muscles

63
Q

Describe contraction extrafusal fibres

A

Skeletal muscle fibres innervated by alpha motor neurons
Generate tension by contracting which allows skeletal movement
Attached to bone by fibrous tissue extensions

64
Q

What is the function of the patellar reflex?

A

Posture and balance

65
Q

What spinal cord level does flexion for patellar reflex occur?

A

L4

66
Q

Describe a muscle spindle

A

Consists of 3-12 intrafusal fibres

Gamma motor neurons to increase sensitivity

67
Q

Describe gamma motor neurons

A

Drive contraction of edge of intrafusal fibres
Sensory from muscle spindle:
- type 1a and type 2
- wrap around intrafusal fibre
- detect stretch of central non-contracting region using stretch receptors

68
Q

What is the function of the tendon reflex?

A

Prevents overloading
Decreases muscle force to drop load
- sensor fires to decrease contraction

69
Q

Describe the steps of the Golgi tendon reflex

A

1) Neuron from Golgi tendon organ fires
2) Motor neuron is inhibited
3) Muscle relaxes
4) Load is dropped

Module 204 MSK & Immune system (44 decks)

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