Explain how skeletal muscle contraction is stimulated

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A nerve impulse travelling down a motor neurone causes the release of acetylcholine from the synpatic knob into the synaptic cleft. This then diffuses across the synaptic cleft down its concentration gradient and binds to complementary receptors on the sarcolemma. This binding causes the opening of ion channels associated with the acetylcholine receptor, leading to an influx of positive ions and a depolarisation of the sarcolemma which spreads along to invaginations of the membrane known as T tubules. These structures are in close conjunction with sarcoplasmic reticulum, and the depolarisation causes subsequent calcium ion release from the sarcoplasmic reticulum. Calcium ions diffuse through the sarcoplasm and bind to tropinin, intiating the sliding of the myosin and actin filaments and the contraction of skeletal muscle. 

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