Action Potential in the synaptic knob of the pre-synaptic neurone causes voltage-gated calcium channels to open. Calcium ions diffuse into the synaptic knob.
Calcium ions cause synaptic vesicles of the neurotransmitter acetylcholine to fuse with the pre-synaptic membrane and release the neurotransmitter into the cleft (exocytosis)
Acetylcholine diffuses across the cleft and binds with receptors on the Na+ ion channels in the post-synpatic sarcolemma membrane. The channels open
Na ions diffuse across the postsynaptic membrane into the sarcolemma. this gnrates an excitory postsynpatic potential and if a threshold level is reached, itcauses a wave of depolarisation.
The wave of depolarisation travels down the tubules (T system) and depolarisation then causes the sarcoplasmic reticulum to release Ca2+ ions
The Ca 2+ ions then bind with the muscle fibres and stimulate a contraction
Acetylcholine is quikcly broken down by acetylcholinase so that contraction only occurs when impulses are continuous
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