szarkolemma

The sarcolemma is the outer membrane of a muscle fiber, also known as a muscle cell. It is a selectively permeable lipid bilayer that encloses the sarcoplasm, which is the cytoplasm of a muscle cell. The sarcolemma plays a crucial role in muscle contraction by transmitting nerve impulses and generating electrical potentials.

Upon receiving a signal from a motor neuron at the neuromuscular junction, the sarcolemma depolarizes. This electrical excitation propagates along the sarcolemma and into the interior of the muscle fiber via invaginations called transverse tubules, or T-tubules. These T-tubules are continuous with the sarcolemma and allow the electrical signal to reach the sarcoplasmic reticulum, a specialized endoplasmic reticulum that stores calcium ions.

The depolarization of the sarcolemma triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm. These calcium ions then bind to regulatory proteins within the muscle fiber, initiating a cascade of events that leads to muscle contraction. Following contraction, the sarcolemma actively pumps calcium ions back into the sarcoplasmic reticulum, allowing the muscle fiber to relax. The sarcolemma also contains various proteins, including ion channels, receptors, and structural proteins, which contribute to its functions and help maintain the integrity of the muscle fiber.