How does an action potential initiate a muscle contraction?
The nerve generates an action potential and it arrives at the axon terminal where it causes a change in the voltage of the axon terminal membrane, thereby causing the calcium channels to open. This allows calcium ions to enter the axon terminal which causes the release of ACh (acetylcholine). As the ACh is released it attaches to the motor end plate and the calcium ions are pumped out of the axon terminal. Next, the chemically regulated ion channels on the motor end plate open and an influx of sodium ions, and efflux of potassium ions occurs. This causes a depolarization of the motor end plate. The ACh diffuses from the motor end plate and the ion channels close. The depolarization of the motor end plate then moves along the sarcolemma and down theT-tubules. This depolarization of the T-tubules causes the terminal cisternae to release calcium ions into the cytosol of the muscle cell. The calcium binds with troponin and causes the tropomyosin complex to shift, thereby exposing the myosi
