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Musculoskeletal system > Muscle cell physiology > Flashcards

Muscle cell physiology Flashcards

1
Q

What are the three types of muscle cell?

A

Skeletal, cardiac, smooth

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2
Q

Morphology of skeletal muscle

A

Long and cylindrical

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3
Q

Morphology of cardiac muscle

A

Branched

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4
Q

Morphology of smooth muscle

A

Spindle/fusiform

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5
Q

Nuclei distribution of skeletal muscle

A

Multiple, located peripherally

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6
Q

Nuclei distribution of cardiac muscle

A

1/2 located centrally

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7
Q

Nuclei distribution of smooth muscle

A

One located centrally

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8
Q

Does skeletal muscle have a sarcomere?

A

Yes - striated pattern

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9
Q

Does cardiac muscle have a sarcomere?

A

Yes - striated pattern

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10
Q

Does smooth muscle have a sarcomere?

A

No

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11
Q

Does skeletal muscle have T-tubules?

A

Yes, forms triad with sarcoplasmic reticulum

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12
Q

Does cardiac muscle have T-tubules?

A

Yes, forms diad with sarcoplasmic reticulum

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13
Q

Does smooth muscle have T-tubules?

A

No - caveolae

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14
Q

Does skeletal muscle have electrical coupling of cells?

A

No

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15
Q

Does cardiac muscle have electrical coupling of cells?

A

Yes - intercalated disks with gap junctions

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16
Q

Does smooth muscle have electrical coupling of cells?

A

Yes - gap junctions

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17
Q

Can skeletal muscle regenerate?

A

Yes - satellite cells

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18
Q

Can cardiac muscle regenerate?

A

No

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19
Q

Can smooth muscle regenerate?

A

Yes

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20
Q

Does mitosis take place in skeletal muscle?

A

No

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21
Q

Does mitosis take place in cardiac muscle?

A

No

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22
Q

Does mitosis take place in smooth muscle?

A

Yes

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23
Q

Does skeletal muscle have extracellular calcium for contraction?

A

No

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24
Q

Does cardiac muscle have extracellular calcium for contraction?

A

Yes

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25
Q

Does smooth muscle have extracellular calcium for contraction?

A

Yes

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26
Q

Regulation of cross-bridge formation in skeletal muscle

A

Ca 2+ binds to troponin

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27
Q

Regulation of cross-bridge formation in cardiac muscle

A

Ca 2+ binds to troponin

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28
Q

Regulation of cross-bridge formation in smooth muscle

A

Ca2+ calmodulin activation of myosin kinase and phosphorylation of myosin

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29
Q

Control of contraction in skeletal muscle

A

Motor neurons

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30
Q

Control of contraction in cardiac muscle

A

Autonomic nerves - beta-adrenergenic agonists

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31
Q

Control of contraction in smooth muscle

A

Autonomic nerves - hormones

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32
Q

Is there summation of twitches by increased stimulus frequency in skeletal muscle?

A

Yes

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33
Q

Is there summation of twitches by increased stimulus frequency in cardiac muscle?

A

No

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34
Q

Is there summation of twitches by increased stimulus frequency in smooth muscle?

A

Yes

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35
Q

Does tension vary with filament overlap in skeletal muscle?

A

Yes

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36
Q

Does tension vary with filament overlap in cardiac muscle?

A

Yes

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37
Q

Does tension vary with filament overlap in cardiac muscle?

A

Yes

38
Q

How long are muscle fibres?

A

Up to 30cm

39
Q

Diameter of muscle fibres

A

10-100 micrometres

40
Q

What are the smaller units of muscle fibres?

A

Myofibrils

41
Q

What is the sarcolemma?

A

Specialised plasma membrane

42
Q

What is the sarcoplasm?

A

Contains glycosomes and myoglobin

43
Q

What are myofibrils?

A

Composed of overlapping thick filaments (myosin) and thin filaments (actin)

44
Q

Why do myofibrils appear striated?

A

A bands are dark (thick and thin filaments)

I bands are light (thin only)

45
Q

What is the sarcomere?

A

Repeating contractile unite between myofibrils

Extend between z-lines

46
Q

Why are the nuclei of muscle fibres peripherally located?

A

The inside is full of myofibrils

47
Q

From smallest to biggest, place fibre, myofibrils and fascicles

A

Fascicles - fibre - myofibrils

48
Q

What are T-tubules?

A

Holes between myofibrils which go to centre and form triad with sarcoplasmic reticulum (t-tubule with SR either side)

49
Q

Where is calcium stored in the SR?

A

Lateral sacks

50
Q

Why are muscles able to generate lots of ATP?

A

Lots of myoglobin and mitochondria

51
Q

How are muscles stimulated to contract?

A

Impulse travels along t-tubules and activates receptors on SR to release calcium into myofibrils

52
Q

How many heads do thick filaments have and what do they do?

A

2 heads - one for ATP and another for actin

53
Q

How many actin filaments do the thin filaments have and what are they?

A

Troponin and tropomyosin

54
Q

What does tropomyosin do initially?

A

Blocks myosin binding site on actin

55
Q

What are the 3 types of troponin?

A 
Troponin C (calcium binds)
Troponin I (inhibitory)
Troponin T (binds to tropomyosin)
56
Q

What happens to troponin C and I when calcium is released by the SR?

A

Calcium binds to troponin C which forces a change in troponin I to release tropomyosin

57
Q

What is a myosin bridge?

A

Myosin head bound to actin

58
Q

What is the cross-bridge lining?

A

Calcium dependent, ATP driven attachment, bending and release of myosin across bridges from myosin binding sites which moves actin filaments towards sarcomere

59
Q

Describe excitation-contraction coupling

A

Electrical impulse conducted along sarcolemma from NMJ
T-tubules direct signal to deep within SR
Direct mechanical coupling between DHPR and RyR
Calcium released from lateral sacks of SR (via RyR) binds to troponin on actin filaments, imitating cross-bridge cycling and muscle contraction
Calcium driven back into SR by ATP-driven pumps

60
Q

What does DHPR stand for?

A

Dihydropyridine receptor

61
Q

What does RyR stand for?

A

Ryanodine receptor

62
Q

Describe the four stages of muscle contraction

A

1) Myosin ATPase splits ATP into ADP and Pi but both remain bound to cross-bridges as stored energy
Myosin active site on actin concealed by tropomyosin and inhibited by actin binding to inhibitory region of troponin
2) Calcium released from SR upon excitation binds to troponin
Triggers conformational change in filament
Troponin I inhibitory region detaches from actin and tropomyosin moves away from myosin binding site
Myosin cross bridges attach to actin filaments
3) ADP and Pi release energy to generate power stroke
Myosin and actin filaments slide across each other and sarcomeres contract

63
Q

Where is calcium stored?

A

Sacs in sarcoplasmic reticulum

64
Q

What is a triad?

A

T-tubule surrounded by two layers of SR

65
Q

What is the terminal cisternae?

A

Flat section of the SR

66
Q

Which band is the dark band?

A

A

67
Q

Which band is the light band?

A

I

68
Q

What is the m-line?

A

Tails of the thick filament wrap around each other

69
Q

Where are z-disks found?

A

End of sarcomere

70
Q

How does information travel across the neuromuscular junction?

A

Reaches terminal bouton of motor neuron
Action potential opens voltage gated ion channels when calcium moves in (depolarisation)
Calcium moving in leads to vesicles of ACh fusing with membrane and releasing ACh into cleft
ACh binds to receptors on motor endplate (motor neurone directly innervates muscle fibres)
Nicotinic ACh receptor is the sodium channel gated by ACh
ACh binds to receptor and opens the pore, letting sodium in
Generates new action potential
More channels that open, more sodium moves in
Leads to EPP

71
Q

How is an electrical impulse switched off?

A

ACh broken down by AChesterase to form choline and acetate
Choline re-uptaken by co-transport with sodium into motor neurone
Repackaged with acetyl to from CoA into vesicles to start again

72
Q

What is the excitation-contraction coupling process?

A

Wave of depolarisation along sarcolemma as sodium channels open and sodium enters
Travels down T-tubules (invaginations of sarcolemma)
Opens voltage gated channels (L-type calcium channel) on DHPR
Voltage gated channel changes on depolarisation and opens RyR receptor
Calcium moves into sarcoplasm
Calcium binds to troponin C to initiate muscle contraction

73
Q

What kind of molecule is RyR?

A

Ligand gated calcium channel

74
Q

How do you switch off excitation-contraction coupling?

A

SERCA pumps calcium into SR using ATP

Calcium gets ‘mopped up’ by calsequetrin which overcomes repulsion between charges to hold calcium together

75
Q

How are muscles stimulated to contract?

A

Calcium binds to troponin C
ATP broken into ADP and Pi which bind to myosin head
Myosin head is ‘cocked’
Calcium binding to TnC switches on thin filament
Conformational change to thin filament - Tm moves, switches filament on
Myosin croc-bridges form with binding site on actin
Conformational change occurs in myosin head to create power stroke
Releases ADP and Pi
ATP binds to myosin ATPase
Cross bridge (myosin head) detaches from actin
ATP hydrolysed to ADP and Pi - binds to myosin head
Myosin head is ‘re-cocked’

76
Q

What happens to z-lines the muscles contract?

A

Move inwards

77
Q

What happens to sarcomeres when muscles contract?

A

Shorten and thicken

78
Q

What happens to A-bands and I-bands when muscles contract?

A

A-bands retain width

I-bands get thinner

79
Q

How is ATP used in muscle contraction?

A

When bound to myosin, it is hydrolysed to ADP and Pi
Once bound, the ADP and Pi are released
Myosin has no ATP
ATP made in sarcoplasm and reattaches to myosin

80
Q

How is energy supplied to the SERCA pump?

A

Creatine phosphate - immediate source of ATP and phosphate
Oxidative phosphorylation - main soured when O2 present
Glycolysis - main source when no O2

81
Q

What are the two types of muscle fibres based on speed of contraction?

A 
Slow fibres (type I)
Fast fibres (type II)
82
Q

What are slow oxidative fibres for?

A

Fatigue resistant, endurance

83
Q

What are fast oxidative fibres for?

A

Sprinting, moderately fatigue resistant

84
Q

What are fast glycolytic fibres used for?

A

Rapid powerful movements but fatigue quickly

85
Q

What is a muscle spasm?

A

Sudden and involuntary transient muscle contraction

86
Q

What is muscle cramp?

A

Involuntary, tetanic muscle contraction

87
Q

What is muscle atrophy?

A

Wasting/decrease in size of muscle due to disease

88
Q

What is muscle strain?

A

Muscle pain and inflammation caused by overuse

89
Q

What is a muscle sprain?

A

Treating of ligaments around a joint due to excessive joint movement

90
Q

Characteristics of slow oxidative fibres

A

Many mitochondria, dense capillary supply, high myoglobin content, thin, low myosin ATPase

91
Q

Characteristics of fast glycolytic fibres

A

Few mitochondria, few capillaries, high glycogen content, large diameter, high myosin ATPase activity

92
Q

Which stain is used to see muscles?

A

Myosin ATPase

Musculoskeletal system (24 decks)

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