Sarcoplasm

Sarcoplasm is the <a href="/facts/Cytoplasm/Wa0sE6xf">cytoplasm</a> of a <a href="/facts/Muscle_cell/cP7Jea3q">muscle cell</a>. It is comparable to the cytoplasm of other cells, but it contains unusually large amounts of <a href="/facts/Glycogen/kWa8fPFE">glycogen</a> (a polymer of glucose), <a href="/facts/Myoglobin/n6h2yBCJ">myoglobin</a>, a red-colored protein necessary for binding oxygen molecules that diffuse into <a href="/facts/Myofibril/uGRRhxms">muscle fibers</a>, and <a href="/facts/Mitochondria/ErHqrdJ1">mitochondria</a>. The <a href="/facts/Calcium/hf252CC0">calcium</a> ion concentration in sarcoplasm is also a special element of the muscle fiber; it is the means by which <a href="/facts/Muscle_contraction/EbloCYfV">muscle contractions</a> take place and are regulated. The sarcoplasm plays a critical role in muscle contraction as an increase in Ca2+ concentration in the sarcoplasm begins the process of filament sliding. The decrease in Ca2+ in the sarcoplasm subsequently ceases filament sliding. The sarcoplasm also aids in pH and ion balance within muscle cells.
It contains mostly <a href="/facts/Myofibrils/uGRRhxms">myofibrils</a> (which are composed of <a href="/facts/Sarcomere/9jQ5DaTz">sarcomeres</a>), but its contents are otherwise comparable to those of the cytoplasm of other cells. It has a <a href="/facts/Golgi_apparatus/F91pGb3t">Golgi apparatus</a> near the <a href="/facts/Cell_nucleus/D7sFRa3c">nucleus</a>, <a href="/facts/Mitochondria/ErHqrdJ1">mitochondria</a> just inside the cell membrane (<a href="/facts/Sarcolemma/s62stjxE">sarcolemma</a>), and a <a href="/facts/Smooth_endoplasmic_reticulum/DVbLA7GE">smooth endoplasmic reticulum</a> (specialized for muscle function and called the <a href="/facts/Sarcoplasmic_reticulum/5tSqPRlk">sarcoplasmic reticulum</a>).
While sarcoplasm and myoplasm, viewed etymologically, might seem to be synonyms, they are not. Whereas sarcoplasm is a type of cytoplasm, myoplasm is the entire contractile portion of <a href="/facts/Muscle_tissue/lF2eqq8h">muscle tissue</a>.
While some authors argue that the proteins and other molecules within the <a href="/facts/Sarcoplasmic_reticulum/5tSqPRlk">sarcoplasmic reticulum</a> lumen technically belong to the sarcoplasm. These molecules are not part of the <a href="/facts/Sarcoplasmic_reticulum/5tSqPRlk">sarcoplasmic reticulum</a> membrane itself but reside within the enclosed sarcoplasmic reticulum space. In that sense, one could say the <a href="/facts/Sarcoplasmic_reticulum/5tSqPRlk">sarcoplasmic reticulum</a> has a type of specialized sarcoplasm.

Sarcoplasm open-in-new

Sarcoplasm