Sarcolemma

Sarcolemma

The sarcolemma is the fine transparent tubular sheath that envelops the fibers of skeletal muscles. It consists of a plasma membrane and an outer coat made up of a polysaccharide substance that is rich in collagen and glycoproteins. The sarcolemma plays a crucial role in the contraction of skeletal muscles by conducting electrical impulses from the nervous system to the muscle fibers.

Structure

The sarcolemma is a specialized cell membrane which surrounds striated muscle fiber cells. It is similar in structure to the plasma membrane of other cells but has additional layers of polysaccharide and collagen. These additional layers provide the sarcolemma with its unique properties, including its ability to conduct electrical impulses and its role in muscle contraction.

Function

The primary function of the sarcolemma is to conduct electrical impulses from the nervous system to the muscle fibers. These impulses trigger the release of calcium ions from the sarcoplasmic reticulum, a specialized form of endoplasmic reticulum in muscle cells. The calcium ions then interact with the contractile proteins within the muscle fibers, leading to muscle contraction.

The sarcolemma also plays a role in maintaining the structural integrity of the muscle fibers. It provides a barrier between the muscle fibers and the surrounding extracellular fluid, helping to maintain the correct ionic balance within the muscle cells.

Clinical significance

Damage to the sarcolemma can lead to a number of muscle disorders. For example, in muscular dystrophy, a genetic disorder that causes progressive muscle weakness, the sarcolemma is often damaged or dysfunctional. This can lead to an increase in the permeability of the sarcolemma, allowing substances that are normally kept out of the muscle cells to enter, leading to cell damage and death.

See also

• Muscle fiber
• Sarcoplasmic reticulum
• Muscular dystrophy

References

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