The sarcolemma is a specialized cell membrane which surrounds striated muscle fiber cells. Sometimes called the myolemma, the sarcolemma is similar to a typical plasma membrane but has specialized functions for the muscle cell. The sarcolemma also contains an extracellular matrix consisting of various polysaccharides which allows the cell to anchor into the tissues that build and support muscle fibers. Typically, the sarcolemma connects the basement membrane which surrounds all connective tissues, or to other muscle cells, creating a very strong fiber which can contract together.
Function of the Sarcolemma
The sarcolemma has several unique features which function in providing muscle cells with both the structure and resources to function. The sarcolemma is very large, compared to some cell membranes, and must be constantly maintained to cover the many myofibrils which make up a muscle cell. The sarcolemma of one cell will attach through extracellular connections to the cell next to it, eventually leading to tendons which attach the muscles to the bones. Through contracting against these levers, muscle cells generate movement in a body.
Due to the high demand of energy needed by these contractions, the sarcolemma is specially formed with channels that carry materials into and out of the cell. As seen the picture below, these small entry points form channels throughout muscle cells which can carry glucose, nutrients, and ions to the many mitochondria present in the cells. These many channels also help restore the membrane potential disturbed when a motor neuron gives a muscle a signal to contract. The sarcolemma, in response to the signal sent by the neuron will generate an action potential down its length, telling the proteins inside the cell to contract.
Besides the specialized functions required by the high energy demand of muscle tissue, the sarcolemma functions as a normal cellular membrane. It contains a number of embedded proteins that work in unison to control the contents of the cell. As with all cell membranes, the sarcolemma is formed from phospholipids, which affects the flow of water, ions, and other molecules. The sarcolemma of different species may have many different proteins and compositions, which reflect the various evolutionary needs of the species over time.