Sarkolemma

Sarkolemma, also known as the sarcolemma, is the plasma membrane that encloses a skeletal or cardiac muscle fiber. It forms the boundary between the intracellular sarcoplasm and the extracellular space, and interfaces with the surrounding endomysium. The term derives from Greek roots meaning flesh and skin or sheath.

Structurally, the sarcolemma is a phospholipid bilayer containing integral and peripheral proteins, ion channels, receptors, and transporters. At the neuromuscular junction, it hosts acetylcholine receptors that mediate signal transmission from motor neurons. The membrane extends into the cell interior through transverse tubules (T-tubules), which propagate action potentials from the surface into the depth of the fiber to trigger contraction. The sarcolemma is also anchored to the cytoskeleton and extracellular matrix via costameres, including the dystrophin-glycoprotein complex, which helps maintain membrane integrity during muscle activity.

Functionally, the sarcolemma maintains ion gradients and electrical excitability through channels and pumps, and couples depolarization to calcium release from the sarcoplasmic reticulum via interactions between voltage sensors on the T-tubules and calcium-release channels. It participates in membrane repair, signaling, and metabolic exchange with surrounding tissue, helping coordinate muscle contraction and homeostasis.

Clinical significance, defects in sarcolemmal proteins such as dystrophin can compromise membrane integrity and lead to muscular dystrophies. Membrane instability or injury can contribute to muscle fiber degeneration, impaired function, and inflammatory responses.