3. Physiology
        3.10. Muscle
            3.10.1. Muscle structure
3.10.1.1. Skeletal muscle

Skeletal muscle

[Ref: WG21:Chp3]

Action potential

Muscle twitch

Starts 2ms after start of depolarisation, before repolarisation is complete

Excitation-contraction coupling

In resting muscle

Contraction

AP travels down nerve

--> Acetylcholine at neuromuscular junction (NMJ)

--> Acetylcholine binds to nicotinic acetylcholine receptors on muscle end-plate

--> Depolarisation of the end-plate

--> AP propagated over muscle membrane

--> AP travels along T-tubules

--> Triggers release of Ca2+ from terminal cisterns
* via dihydropyridine receptors

--> Ca2+ binds to troponin C

--> Weakens binding of troponin I to actin

--> Tropomyosin moves laterally

--> Binding site on actin (for myosin) exposed

When binding site on actin is exposed

--> Myosin head binds to actin

--> Myosin head bends and utilises one ATP

--> Sarcomere shortens by about 10nm

--> Myosin head detaches

Dihydropyridine receptor

Ending contraction

--> Sarcoplasmic reticulum actively transport Ca2+ back into its longitudinal portion
* by Ca-Mg ATPase pump

--> Ca2+ diffuse back into terminal cisterns

--> Ready for release when AP arrives

--> Once Ca2+ outside the reticulum dropped enough, contraction ceases 

NB:

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Created20050605
Reviewed20050605


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