Explain the events leading up to a skeletal muscle twitch, starting with the arrival of neurotransmitter in the neuromuscular junction.
What will be an ideal response?
Acetylcholine binds to its receptor (nicotinic cholinergic) on the skeletal muscle cell membrane. This increases in flux of cations across the membrane of which the influx of Na is greater than the efflux of K, which causes the membrane to depolarize (end-plate potential). This depolarization activates the voltage gated Na channels responsible for an action potential and the action potential travels along the sarcolemma. In addition to the sarcolemma, the action potential travels along the T-tubule causing change in the L-type Ca channel (dihydropyridine receptor) that is linked to a ryanodine receptor in the sarcoplasmic reticulum. This opens the ryanodine receptor causing calcium to diffuse out of the sarcoplasmic reticulum. The calcium binds to troponin and moves the tropomyosin out of the way such that a high force crossbridge can form between actin and myosin. The myosin head is then able to undergo its power stroke and force is generated.
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