Exercise Phys (11) : Structure and regulation of skeletal muscle Flashcards Preview

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Flashcards in Exercise Phys (11) : Structure and regulation of skeletal muscle Deck (10)
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1
Q

Structural components of skeletal muscle spindle?

A

Made from sarcomere functional unit of striated muscle

A band

  • myosin filaments
  • M band (myosin filaments attach here)

I band
- actin thin filaments

Z line/disk
(thin filaments attach here)

2
Q

Thick filaments are formed from what?

A

Myosin II molecules

regulatory light chain, alkali light chain, heads of myosin heavy chain, alpha helix tail region

3
Q

Thin filaments are formed from what?

A

Actin

Troponin complex
Tropomyosin
Myosin binding site

4
Q

What is the function of titin and where is it found?

A

Titin forms arrays of fine filaments that stabilise the myosin filament positions - extends from Z disk to M line

Very large molecule

Provides increased force when muscle is stretched, resists over-stretching

5
Q

Describe the pathway of muscle contraction as an action potential arrives at a muscle cell

A

Action potential arrives at muscle cell, depolarises sarcolemma -> depolarises T-tubules, open voltage-gated DHPR Ca2+ channels

  • > mechanical coupling of DHPR to RYR triggers the release of Ca2+ from storage in sarcoplasmic reticulum via RYR ca2+ channels
  • > Ca2+ binds to troponin, causes conformational change, tropomyosin pulled away from myosin binding sites
  • > myosin heads binds and initiates cross bridge cycling
  • > As long as Ca++ ions remain in the sarcoplasm, and as long as ATP is available to drive the cross-bridge cycling + pulling of actin strands by myosin, the muscle fiber will continue to shorten to an anatomical limit
6
Q

How is cross bridge cycling terminated?

A

Ca2+ is pumped back into SR via SERCA

7
Q

Types of muscle fibre? Uses?

A
Type I (slow twitch) ~ 50% muscle fibres in average musc
- peak tension in 110ms

Type II

  • IIa (fatigue resistant) ~25%
  • IIx (fast fatigue) ~25%
  • peak tension 50ms
8
Q

Main differences between type I and type II fibres?

A

Speed of myosin ATPase
- faster myosin ATPase in type II -> faster contraction

SR
- type II have more developed SR -> 3-5 times faster calcium release

Motor units
- type II larger motor units (>300 fibres)

9
Q

Metabolic activity of each type of fibre?

A

Type I
- slow oxidative

Type IIa
- fast oxidative/glycolytic

Type IIx
- glycolytic

10
Q

Muscle fibre roles during exercise?

A

I -> high aerobic endurance, used in low intensity aerobic exercise, daily activities

II
a -> fatigue resistant, used in ~ 1600m
x -> fast fatigue, used in ~100m

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