Scientists do not really know what the sarcolemma does. They do know that it is the membrane that encloses the muscle cell. It is semipermeable and about 100 Angstroms thick.Continue Reading
Because the sarcolemma is so thin, it is difficult to study. Scientists believe it is made out of the same lipoproteins that make up the structures of other animal cells.
They also know that the sarcolemma contains holes that lead to transverse tubules, or T-tubules. They do not open inside the muscle cell but go around it, rather like plumbing pipes, and open up in another area of the sarcolemma. The tubules' task is to transmit impulses from the sarcolemma to the sarcoplasmic reticulum.
This process plays a role in muscle contraction, because it allows calcium ions to be released into the sarcoplasmic reticulum. The sarcoplasmic reticulum stores these calcium ions and releases them into the sarcoplasm when a muscle is stimulated. The calcium ions work with proteins to cause a muscle to contract.
Sarcoplasm is simply the cytoplasm of a muscle cell. It is similar to the cytoplasm that makes up the interior of other cells but it has large stores of glycogen. Biological "pumps" allow a steady stream of calcium ions from the sarcoplasm into the sarcoplasmic reticulum.Learn more about Cells