Congenital Myopathies

How Ion Channels Regulate Muscle Contraction

Acetylcholine leaves the nerve fiber and docks on receptors in the muscle membrane, causing that area of the muscle fiber to become slightly more positive (“depolarized”).

Sodium channels open in response to this small depolarization, permitting a huge flow of positively charged sodium ions to enter the muscle fiber. The depolarization is greatly amplified, and a brief electrical impulse (“action potential”) spreads throughout the fiber.

Depolarization of the muscle fiber is sensed by calcium channels and triggers the release of calcium ions from internal storage areas. This flood of released internal calcium is the chemical signal that causes the thick and thin filaments of the muscle fiber to slide past each another (contract).