Sarcoplasm is the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

of a

muscle cell A muscle cell, also known as a myocyte, is a mature contractile Cell (biology), cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal muscle, skeletal, smooth muscle, smooth, and Cardiac muscle, cardiac ...

. 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. It is the main storage form of glucose in the human body. Glycogen functions as one of three regularly used forms ...

(a polymer of glucose),

myoglobin Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle, skeletal Muscle, muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compar ...

, a red-colored protein necessary for binding oxygen molecules that diffuse into

muscle fiber A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). A skeletal muscle cell is long and threadl ...

s, 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 us ...

.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; it has 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 to it ...

ion concentration in sarcoplasm is also a special element of the muscle fiber; it is the means by which

muscle contraction Muscle contraction is the activation of Tension (physics), 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 musc ...

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. The 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 myofibr ...

(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 striated muscle, Skeletal muscles are composed of tubular ...

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 Cell (biology), cells. Part of the endomembrane system in the cytoplasm, it protein targeting, packages proteins ...

near the nucleus,

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 fibre or a cardiomyocyte. It consists of a lipid bilayer and a thin ...

), and a smooth endoplasmic reticulum (specialized for muscle function and called the sarcoplasmic reticulum). 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 is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to contract. ...

. While some authors argue that the proteins and other molecules within the sarcoplasmic reticulum lumen technically belong to the sarcoplasm. These molecules are not part of the sarcoplasmic reticulum membrane itself but reside within the enclosed sarcoplasmic reticulum space. In that sense, one could say the sarcoplasmic reticulum has a type of specialized sarcoplasm.

References

External links

Merriam-Webster Dictionary

{{Authority control Cell anatomy