Neuromuscular junction activation. Animation showing the process by which the neuromuscular junction, a synapse between a nerve fibre and a muscle fibre, is activated. The nerve ending is at left, with the muscle membrane (sarcolemma) at right. The process is driven by calcium ions (red). The animation starts with the arrival of a nerve impulse (glow), temporarily changing the membrane potential from positive to negative. This triggers an influx of calcium through a voltage-gated ion channel (lower left). The calcium ions bind to a vesicle (pink) containing the neurotransmitter acetylcholine (ACh, orange and purple). The vesicle releases ACh through the terminal nerve membrane (neurolemma) into the synaptic gap. ACh then binds to a channel (yellow) on the post-synaptic muscle cell membrane (sarcolemma) and triggers an influx of sodium ions (blue). The resulting action potential (glow) triggers further calcium channels (orange and green). The final effect is to trigger ion channels in the sarcoplasmic reticulum (oval) which releases yet more calcium ions that cause muscle contraction. For this animation without labels, see K004/2045.
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