Sarcolemma

The sarcolemma is the specialized plasma membrane surrounding a muscle fiber. It encloses the cell, conducts electrical signals, and connects with structures that carry signals into its interior.

Action potential: A rapid, transient change in a cell’s membrane voltage that can propagate as an electrical signal. An action potential travels along the sarcolemma to initiate excitation of the muscle fiber.
Plasma membrane: A selectively permeable lipid bilayer that encloses a cell and regulates exchange with its surroundings. The sarcolemma is the muscle-specific form of this general cellular boundary.
Duchenne muscular dystrophy: An X-linked genetic disorder causing progressive muscle weakness, usually due to absent functional dystrophin. Dystrophin loss destabilizes the muscle-fiber membrane during repeated contraction.
Basal lamina: A thin extracellular matrix layer that supports cells and separates them from surrounding tissue. It lies outside the sarcolemma and helps organize the muscle fiber’s extracellular interface.
Transverse tubule: An inward extension of the cell membrane that carries electrical signals deep into a muscle fiber. These sarcolemmal invaginations bring excitation close to the contractile machinery.
Phospholipid bilayer: A double layer of phospholipid molecules that forms the basic structure of cell membranes. This bilayer provides the structural foundation of the sarcolemma.
Dystrophin: A large cytoskeletal protein that links the muscle-cell interior to a protein complex at the membrane. It helps reinforce the sarcolemma against mechanical stress.
Costamere: A protein assembly that links a muscle fiber’s internal cytoskeleton to the extracellular matrix at the sarcolemma. Costameres anchor the membrane and transmit force laterally from contracting structures.
Excitation–contraction coupling: The process linking an electrical change in a muscle cell to the calcium signals that trigger contraction. It connects sarcolemmal excitation to the intracellular events that produce contraction.
Ion channel: A membrane protein that allows selected ions to cross a biological membrane. Ion channels in the sarcolemma create and shape muscle-fiber electrical signals.

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