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Physiology > Muscle physiology > Flashcards

Muscle physiology Flashcards

1
Q

Which of the three muscle types have pacemaker cells?

A 
Cardiac m
Smooth m (in single-unit muscle)
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2
Q

List the three muscle types in order of increasing speed of contraction.

A

Smooth, cardiac, skeletal

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3
Q

Which of the three muscle types have T tubules?

A

Skeletal and cardiac

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4
Q

What are muscle fascicles?

A

Groups of muscle fibres, surrounded by perimysium

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5
Q

Name four scaffold proteins in muscle fibres.

A

Desmin, titin, obscurin, nebulin

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6
Q

What is the function of desmin?

A

Intermediate filament that:
Forms scaffolds between Z lines
Allows side-side organisation and large force generation
Connects mitochondria and the nucleus to the Z-disks and
Binds the myofibrils to the sarcolemma

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7
Q

What is titin?

A 
Scaffold protein that: 
Stabilises the myofibril
Anchors the thick filament to the Z disk
Acts as a tension sensor, allowing an appropriate response. 
Largest protein in the body.
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8
Q

What is obscurin?

A

Connects the myofibril to the sarcoplasmic reticulum, allowing communication

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9
Q

What is nebulin?

A

Scaffold protein with own kinase activity; interacts with desmin to determine Z disk width and stabilise actin filaments.

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10
Q

How long does the creatine store in muscle lasts?

A

10 seconds

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11
Q

How long does the glycogen store in muscle last?

A

From 10 seconds to a few minutes

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12
Q

Can the amount of time the glycogen supply in muscle is used for be altered by training?

A

By a small amount

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13
Q

For how long can muscle use oxidative, aerobic pathway?

A

Hours

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14
Q

What is the colour difference between fast and slow twitch muscles?

A

Fast twitch- pale

Slow twitch - dark due to myoglobin

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15
Q

Do larger diameter motor neurons lead to more rapid or slower contraction?

A

Rapid

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16
Q

Do sarcomeres shorten in length during muscle contraction?

A

Yes

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17
Q

Describe the positioning of the sliding filaments at rest.

A

Some overlap

Myosin heads are cocked, with is ATP-dependent

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18
Q

Describe thick filaments

A

Polypeptides made of 2 large heavy chains and 4 light chains with two globular heads containing an ATP binding site each, with a long tail.

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19
Q

What is tension in a muscle fibre and therefore, produced force, proportional to?

A

Number of cross-bridges between thick and thin filaments

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20
Q

What are the two roles of ATP in cross-bridge cycling?

A

Hydrolysis of ATP is required for the power-stroke

ATP binding is required for release of filament binding

21
Q

What is the role of Ca2+ in cross-bridge cycling?

A

Binds to troponin to change orientation of tropomyosin to expose myosin binding sites.

22
Q

How does the actin-myosin motility assay work?

A

Line up myosin heads, and run and actin filament through in the presence of Ca2+

23
Q

Where is the major supply of Ca2+ in skeletal muscle from?

A

Sarcoplasmic reticulum

24
Q

Where is the major supply of Ca2+ in cardiac muscle from?

A

Extracellular

25
Q

What type of transport is used to transport Ca2+ into sarcoplasmic reticulum following contraction?

A

Active transport via pumping.

26
Q

Which proteins allow vesicle binding to the axon membrane to allow ACh release?

A

SNARE proteins - SNAP-25 and vesicle-associated membrane protein (VAMP)

27
Q

Which botulinum toxin drug targets which SNARE protein?

A

Botox - SNAP-25

Discort - VAMP

28
Q

What is the target of organophosphate pesticides?

A

Acetylcholinesterase

29
Q

Compare isotonic and isometric contraction.

A

Isotonic - constant tension, muscle changes length

Isometric - constant length, no work done

30
Q

In a contraction cycle, which size muscles are recruited first?

A

Smallest

31
Q

What causes a plateau in the force of muscle contraction?

A

The maximum number of fibres recruited

32
Q

Describe tetanus

A

Constant contraction due to temporal summation of stimuli

33
Q

In which fibres are sarcomeres most disrupted?

A

Fast glycolytic fibres

34
Q

Which speed order are motor units recruited during contraction?

A

Slow (S), then medium fast resistant (FR), then rapid fast fatiguing (RR).

35
Q

Muscle fibres that are the thickest and fastest are of which type?

A

Fast glycolytic

36
Q

What is the importance of phosphocreatine?

A

Serves as an ATP reservoir via activity of creatine kinase

37
Q

What are the effects of exercise on blood glucose levels?

A

GLUT4 transporters increase in muscle, increasing capacity for muscle to transport glucose, decreasing blood glucose levels.
Citrate synthase increases in muscle
Treatment of metabolic disease

38
Q

What is the brief mechanism of GLUT4 upregulation with exercise?

A

Ca2+ causes CaMKI upregulation
ATP depletion increases AMPK
Together, these cause GLUT4 upregulation

39
Q

When do fast twitch fibres develop?

A

Adolescence. Prior to this, there is little to no anaerobic activity, and it should not be used.

40
Q

How does the relative number of muscle fibre types change in puberty?

A

Before puberty, most muscle fibres are of oxidative capacity. Following puberty, there is an increase in muscle mass, proportion of fast-twitch fibres and glycolytic and CrP storage capacity.

41
Q

What are the two phenomenons that occur in muscle with age?

A

Sarcopenia - loss of skeletal muscle fibres

Dynapenia - loss of strength

42
Q

Are age-related sarcopenia and dynapenia modifiable?

A

Yes, with exercise to an extent

43
Q

What is the effect of mTOR activity on protein synthesis?

A

Increases protein synthesis

44
Q

What are negative regulators of mTOR?

A

Hypoxia, corticosteroids, alcohol
Mechanical unloading
Low energy intake

45
Q

What are the positive regulators of mTOR?

A

Growth factor
Mechanical stress
Amino acids

46
Q

Name two factors that determine whether muscle regeneration or muscle degeneration dominates in muscle injury?

A

Age, extent of injury

47
Q

Expression of which gene causes a satellite cell to divide into a satellite cell?

A

Caveolin 1

48
Q

Which circulating molecules regulate levels of satellite differentiation?

A

Androgens, NO, IL-6, immune responses.

Physiology (5 decks)

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