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Flashcards in Muscle physiology Deck (48):
1

Which of the three muscle types have pacemaker cells?

Cardiac m
Smooth m (in single-unit muscle)

2

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

Smooth, cardiac, skeletal

3

Which of the three muscle types have T tubules?

Skeletal and cardiac

4

What are muscle fascicles?

Groups of muscle fibres, surrounded by perimysium

5

Name four scaffold proteins in muscle fibres.

Desmin, titin, obscurin, nebulin

6

What is the function of desmin?

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

7

What is titin?

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.

8

What is obscurin?

Connects the myofibril to the sarcoplasmic reticulum, allowing communication

9

What is nebulin?

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

10

How long does the creatine store in muscle lasts?

10 seconds

11

How long does the glycogen store in muscle last?

From 10 seconds to a few minutes

12

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

By a small amount

13

For how long can muscle use oxidative, aerobic pathway?

Hours

14

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

Fast twitch- pale
Slow twitch - dark due to myoglobin

15

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

Rapid

16

Do sarcomeres shorten in length during muscle contraction?

Yes

17

Describe the positioning of the sliding filaments at rest.

Some overlap
Myosin heads are cocked, with is ATP-dependent

18

Describe thick filaments

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.

19

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

Number of cross-bridges between thick and thin filaments

20

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

Hydrolysis of ATP is required for the power-stroke
ATP binding is required for release of filament binding

21

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

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

22

How does the actin-myosin motility assay work?

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

23

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

Sarcoplasmic reticulum

24

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

Extracellular

25

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

Active transport via pumping.

26

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

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

27

Which botulinum toxin drug targets which SNARE protein?

Botox - SNAP-25
Discort - VAMP

28

What is the target of organophosphate pesticides?

Acetylcholinesterase

29

Compare isotonic and isometric contraction.

Isotonic - constant tension, muscle changes length
Isometric - constant length, no work done

30

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

Smallest

31

What causes a plateau in the force of muscle contraction?

The maximum number of fibres recruited

32

Describe tetanus

Constant contraction due to temporal summation of stimuli

33

In which fibres are sarcomeres most disrupted?

Fast glycolytic fibres

34

Which speed order are motor units recruited during contraction?

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

35

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

Fast glycolytic

36

What is the importance of phosphocreatine?

Serves as an ATP reservoir via activity of creatine kinase

37

What are the effects of exercise on blood glucose levels?

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

What is the brief mechanism of GLUT4 upregulation with exercise?

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

39

When do fast twitch fibres develop?

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

40

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

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

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

Sarcopenia - loss of skeletal muscle fibres
Dynapenia - loss of strength

42

Are age-related sarcopenia and dynapenia modifiable?

Yes, with exercise to an extent

43

What is the effect of mTOR activity on protein synthesis?

Increases protein synthesis

44

What are negative regulators of mTOR?

Hypoxia, corticosteroids, alcohol
Mechanical unloading
Low energy intake

45

What are the positive regulators of mTOR?

Growth factor
Mechanical stress
Amino acids

46

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

Age, extent of injury

47

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

Caveolin 1

48

Which circulating molecules regulate levels of satellite differentiation?

Androgens, NO, IL-6, immune responses.