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acetylcholine binds ligand-gated Na+ channels on the sarcolema (those ligand-gated Na+ channels are called licotenic receptors)
This produces a massive influx of sodium and a massive EPSP
This triggers an action potential across the entire sarcolema (the plasma membrane) that travels dwon the T-tubules and stimulates/triggers the release of calcium from terminal cisternae of the sarcoplasmic reticulum.
That Ca2+ will bind to troponin, causing a conformational change
Troponin is attached to tropomyosiin; and because tropon is attached to tropomyosin, this causes displacement of tropomysoin, thus revealing binding sites on actin
Myosin heads bind to the binding site and pull actin toward the midline, thus shortening the sarcomere and the entire muscle
Ca2+ contraction is terminated when Ca2+ is pumped back into the SR. ATP is required in two places for three reasons
- Three reasons:
- 1) For Ca2+ pumps (needs to pump Ca2+ back into SR; carried out by calciumase)
- 2) has to bind to myosin head before myosin will separate from the actin
- 3) when the ATP is hydrolyzed, the myosin goes into high-energy configuration adn grabs another fiber
Contraction.. (he didn't give it to us yet)
he didn't give it to us yet
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