saroplasma

Saroplasma is a term sometimes used to denote the cytoplasm of a muscle cell or muscle fiber. In modern anatomical usage, the preferred term is sarcoplasm. It is the intracellular medium bounded by the cell membrane (sarcolemma) and contains the cytosol along with specialized organelles and inclusions.

The sarcoplasm houses the cellular machinery needed for muscle function. It contains myofibrils, which are chains of sarcomeres the basic contractile units of muscle, as well as mitochondria, the energy-producing organelles. A network of sarcoplasmic reticulum surrounds the myofibrils and plays a key role in calcium storage and release. The sarcoplasm also contains energy reserves such as glycogen granules and, in many fibers, the pigment myoglobin, which helps store and transport oxygen. Ribosomes and enzymes involved in glycolysis and oxidative metabolism are present to support rapid energy production during muscle activity.

Functionally, the sarcoplasm participates in excitation–contraction coupling. An action potential travels along the sarcolemma and into the transverse tubules, triggering calcium release from the sarcoplasmic reticulum into the sarcoplasm. The sudden rise in intracellular calcium initiates cross-bridge cycling between actin and myosin, leading to contraction. After contraction, calcium is pumped back into the sarcoplasmic reticulum, enabling relaxation and readying the muscle for subsequent activity.

Historically, saroplasma is sometimes encountered as an alternate spelling of sarcoplasm or as an older term for the muscle cytoplasm. The modern term sarcoplasm is standard in physiology and anatomy.