Sarcolemma Definition

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.

Skeletal muscle

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 which work in unison to control the contents of the cell. As 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 reflects the various evolutionary needs of the species over time.

Related Biology Terms

  • Cell Membrane – A double layer of phospholipids which surrounds.
  • Basement Membrane – The lowest layer of the epithelium, made from a number of proteins and polysaccharides.
  • Action Potential – An electrical impulse created by the rapid diffusion of ions across a cell membrane.
  • Motor Neuron – Specialized nerves which carry signals exclusively to muscle cells.

Quiz

1. Why do animals need a specialized cell membrane, or sarcolemma, surrounding their muscle cells?
A. The sarcolemma can stretch and contract well
B. The sarcolemma simply provides more oxygen to the cell
C. The sarcolemma properly balances many ions, nutrients, and oxygen

Answer to Question #1
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