What is the Difference Between Sarcolemma and Endomysium

The main difference between sarcolemma and endomysium is that sarcolemma is the plasma membrane of the muscle fiber whereas endomysium is a thin sleeve of fibrous connective tissue over the muscle fiber.

Sarcolemma and endomysium are two components of a skeletal muscle. Skeletal muscle is an organ in the vertebrate muscular system, attached to the bones through tendons. The structural components of the skeletal muscle include epimysium, perimysium, endomysium, muscle fiber, and blood vessels.

Key Areas Covered

1. What is Sarcolemma
   • Definition, Structure, Function
2. What is Endomysium
   • Definition, Structure, Function
3. Similarities Between Sarcolemma and Endomysium
   • Outline of Common Features
4. Difference Between Sarcolemma and Endomysium
   • Comparison of Key Differences

Key Terms

Endomysium, Sarcolemma

What is Sarcolemma

Sarcolemma or myolemma is the cell membrane of the muscle fiber and the sarcoplasm is the cell membrane of the cytoplasm of the muscle fiber. It contains a lipid bilayer and a thin outer coat of polysaccharide (glycocalyx), contacting the basement membrane. The basement membrane contains numerous thin collagen fibrils and specialized proteins such as laminin that provide a scaffold to which the muscle fiber can adhere. Moreover, transmembrane proteins in the plasma membrane connect the actin skeleton of the muscle cell to the basement membrane and to the exterior of the cell. At each end of the muscle fiber, the surface layer of the sarcolemma fuses with a tendon fiber, and the tendon fibers, in turn, collect into bundles to form the muscle tendons that adhere to bones.

Figure 1: Sarcolemma

Furthermore, the main function of the sarcolemma is similar to the function of the plasma membrane of all eukaryotic cells, which is to act as a barrier between the extracellular and intracellular compartments. Therefore, sarcolemma separates the muscle cell from its surroundings. Also, the sarcolemma is selectively permeable to water through aquaporin channels. It contains membrane proteins that work as ion channels, creating ion gradients. In addition, co-transporters of sarcolemma generate electrical gradients including action potentials.  

What is Endomysium

Endomysium is the wispy layer of areolar connective tissue that ensheaths each individual muscle fiber or muscle cell. It overlies the muscle fiber’s cell membrane: the sarcolemma. Moreover, it is the deepest and smallest component of muscle connective tissue.  It also contains capillaries and nerves. However, the main function of the endomysium is to provide an appropriate chemical environment for the excitation and the subsequent contraction of the muscle fiber. During this process, calcium, sodium, and potassium ions exchange through the sarcolemma of the muscle cell.

Figure 2: Enodmysium

Moreover, endomysium combines with the perimysium and epimysium, creating the collagen fibers of the tendons. The major protein of the endomysium is collagen and mainly type I and type III collagen components occur in the endomysium while type IV and V occur in minor amounts.

Similarities Between Sarcolemma and Endomysium

• Sarcolemma and endomysium are two components of the skeletal muscle structure.
• Moreover, their main function is to help the muscle with the movements of the body parts.

Difference Between Sarcolemma and Endomysium

Definition

Sarcolemma refers to the plasma membrane of the muscle cell and is surrounded by basement membrane and endomysial connective tissue while endomysium refers to a delicate network of connective tissue, which surrounds individual muscle fibers and contains the vessels and nerves that supply the muscle fibers as well as the proteoglycan matrix for ion flux and metabolic exchange.

Structure

Usually, sarcolemma contains two lipid membranes and glycocalyx contacting the basement membrane, while endomysium contains the wispy layer of areolar connective tissue.

Occurrence

The sarcolemma is the plasma membrane of the muscle cell while endomysium overlies the sarcolemma.

Function

The main function of sarcolemma is to act as a selectively permeable barrier while the main function of endomysium is to provide an appropriate chemical environment for the excitation and the subsequent contraction of the muscle fiber.

Conclusion

In brief, sarcolemma and endomysium are two components of the skeletal muscle. The sarcolemma is the plasma membrane of the muscle cell while the endomysium is the overlying connective tissue layer of the sarcolemma. In addition, sarcolemma serves as the selectively permeable barrier of the muscle cell, but the main function of the endomysium is to provide the appropriate chemical environment for the contraction of muscles. Therefore, the main difference between sarcolemma and endomysium is their structure and function.

References:

1. Wikimedia Foundation. (2022, September 4). Sarcolemma. Wikipedia. Retrieved September 5, 2022.
2. Wikimedia Foundation. (2021, July 4). Endomysium. Wikipedia. Retrieved September 5, 2022.

Image Courtesy:

1. “Blausen 0801 SkeletalMuscle ” By BruceBlaus – Own Work (CC By 3.0) via Commons Wikimedia
2. “Illu muscle structure ” By Arcadian  (Public Domain) via Commons Wikimedia