The sliding filament theory describes the process by which muscles contract.

Muscle fibres are made up of myofibrils. Myofibrils comprise of sarcomeres, containing actin and myosin.

1.) A nerve impulse arrives at the neuromuscular junction, releasing acetylcholine.Depolarisation continues down the t-tubules, causing Ca2+ release.

2.) Ca2+ binds to troponin, altering the shape of troponin, causing tropomyosin to move off actin binding sites. Myosin heads are now able to bind to the exposed actin binding sites, forming a cross-bridge.

3.) Hydrolysis of ATP releases energy, allowing myosin to 'cock' its head,pulling actin to create an overlap. This is muscular contraction (shortening).

4.) ATP binds to myosin heads, causing the cross-bridge to be broken.Once the ATP is hydrolysed it can bind to another actin binding site, further down actin. Allowing contraction to continue.

5.) When ATP and Ca2+ are depleted in the muscle contraction terminates. Actin binding sites are covered again with tropomyosin

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