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Sarcoplasm is the
cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
of a
muscle cell A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a mus ...
. It is comparable to the cytoplasm of other cells, but it contains unusually large amounts of
glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one of ...
(a polymer of glucose),
myoglobin Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compared to hemoglobin, myoglob ...
, a red-colored protein necessary for binding oxygen molecules that diffuse into muscle fibers, and
mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...
.Roberts, Michael D.; Haun, Cody T.; Vann, Christopher G.; Osburn, Shelby C.; Young, Kaelin C. (2020). "Sarcoplasmic Hypertrophy in Skeletal Muscle: A Scientific "Unicorn" or Resistance Training Adaptation?". Frontiers in Physiology. 11. . . . . The
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
ion concentration in sarcoplasma is also a special element of the muscle fiber; it is the means by which
muscle contraction Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such a ...
s 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. A decrease in Ca2+ in the sarcoplasm subsequently ceases filament sliding.Shahinpoor, Mohsen (2013). Muscular Biomimicry. Elsevier. pp. 139–160. . The sarcoplasm also aids in pH and ion balance within muscle cells. It contains mostly
myofibrils A myofibril (also known as a muscle fibril or sarcostyle) is a basic rod-like organelle of a muscle cell. Skeletal muscles are composed of long, tubular cells known as muscle fibers, and these cells contain many chains of myofibrils. Each myofi ...
(which are composed of
sarcomere A sarcomere (Greek σάρξ ''sarx'' "flesh", μέρος ''meros'' "part") is the smallest functional unit of striated muscle tissue. It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells (called mus ...
s), but its contents are otherwise comparable to those of the cytoplasm of other cells. It has a
Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles i ...
near the
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
,
mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...
just inside the cell membrane (
sarcolemma The sarcolemma (''sarco'' (from ''sarx'') from Greek; flesh, and ''lemma'' from Greek; sheath) also called the myolemma, is the cell membrane surrounding a skeletal muscle fiber or a cardiomyocyte. It consists of a lipid bilayer and a thin oute ...
), and a
smooth endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ...
(specialized for muscle function and called the
sarcoplasmic reticulum The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca2+). Calcium ion levels are ke ...
). 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
muscle tissue Muscle tissue (or muscular tissue) is soft tissue that makes up the different types of muscles in most animals, and give the ability of muscles to contract. Muscle tissue is formed during embryonic development, in a process known as myogenesis. ...
.


References


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Merriam-Webster Dictionary


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