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Arrival of the Action Potential at the Neuromuscular junction
Impulse (action potential) arrives at axon terminal
Ca++ ions rush in (as action potential activated Ca++ gates); Ca++ reacts with synaptic vesicles
Synaptic vesicles fuse with cell membrane of axon terminal
ACh (acetylcholine) released through a process known as exocytosis
ACh binds with motor end plate receptors: deplorization occurs as Na+ rushes into the muscle cell
Impulse travels through T-tubules which excite the sarcoplasmic reticulum (SR)
Ca++ ions release from the SR
Ca++ binds with troponin
Shift of tropomyosin, which makes the binding sites available for myosin S1 units to bind
With ATP present, ATPase splits (hyrolysis) ATP to ADP and Pi and Energy
Myosin S1 units can now bind to active sites on actin
Sliding action of actin over myosin called the Power Stroke
Impulse stops to muscle; calcium ions pumped back into SR by active transport (energy requiring) pumps
Tropomyosin returns over the active sites on actin and muscle action ceases
STUDENTS, PLEASE GO TO THIS LINK BELOW AND SCROLL DOWN TO CHALLENGE YOURSELF WITH A PRACTICE QUIZ ON THE SEQUENCE OF MUSCLE CONTRACTION
http://www.unm.edu/~lkravitz/Exercise%20Phys/muscle.html
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