Microscopische anatomie van skeletspieren

Each skeletal muscle is composed of multiple bundles of elongated multinucleated muscle cells or muscle fibers.

These cells are enclosed by a plasma membrane commonly known as the sarcolemma.

The sarcolemma invaginates into the cytoplasm to form transverse or T-tubules, which ensure uniform transmission of a neural impulse across the cell.

The cytoplasm of the muscle cell, or the sarcoplasm, contains a large number of mitochondria, glycosomes containing glycolytic enzymes, and oxygen-binding proteins called myoglobin. These cellular components support high energy-demanding muscle cell activity.

The specialized smooth endoplasmic reticulum of the muscle cells, called the sarcoplasmic reticulum, mainly regulates the intracellular calcium levels, depending on the muscle activity.

It wraps around each myofibril — long fine contractile fibers that occupy most of the cell volume.

Each myofibril is further composed of smaller functional units called the sarcomeres, lined from end to end.