notes draft muscle contraction

At the neuromuscular junction, an axon terminal releases acetylcholine into the synapse where they then bind to acetylcholine receptors. The binding of the acetylcholine causes a graded potential or depolarization of the muscle. Once the voltage threshold is met, the voltage gated ion channels open and allow sodium to rush into the cell. This rush of sodium causes a depolarization, and an electric current flows down the plasma membrane of the cell. The electric current passes through the t-tubules of the sarcoplasmic reticulum. The t-tubule surrounds the sarcoplasmic reticulum and once depolarized, it opens calcium channels on the sarcoplasmic reticulum. The free calcium floods the area around the thick and thin filaments and causes a muscle contraction.