Ap Biology Muscle Cells

Muscle Cell at rest:
As the muscle cell is at rest it has a resting potential of -90mV.
The K+ is all located inside the cell, the Na+ is located outside of the cell and the Ca2+ is located inside the sarcoplasmic reticulum. All leak channels and pumps are closed at this point.

Muscle Cell stimulated by Acetylcholine:
A motor neuron releases Acetylcholine which diffuses toward the muscle cell across the neuromuscular junction. As the Acetylcholine binds to a receptor on the muscle cell membrane, it signals the sodium leak channel to open. This causes a localized depolarization to occur.
Soon after this causes the Na+ voltage gated channels to open spreading a wave of depolarization across the membrane and cell.le Cell at rest:
As the muscle cell is at rest it has a resting potential of -90mV.
The K+ is all located inside the cell, the Na+ is located outside of the cell and the Ca2+ is located inside the sarcoplasmic reticulum. All leak channels and pumps are closed at this point.

Muscle Cell starting to Repolarize and Relax then completely repolarized and at rest
When muscle cells begin to repolarize, first the acetychloine is removed from the receptors on the cells. This in turn causes the receptor mediated Na+ leak channels to close. Voltage gated potassium leak channels open as a result. As K+ ions begin coming into the cytoplasm to repolarize. When the membrane potential reaches a specific level, the voltage gated potassium leak channels close as well. The sodium potassium pump works throughtout this process, by pumping Na+ ions out and K+ ions into the cells (using ATP, by a process called active transport).Ca2+ ions are pumped back into the SR by means of active transport. The membrane potential is then restored to the resting potential of -95mv.