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The unusual microscopic anatomy of a muscle cell gave rise to its terminology. The cytoplasm in a muscle cell is termed the sarcoplasm; the smooth endoplasmic reticulum of a muscle cell is termed the sarcoplasmic reticulum; and the cell membrane in a muscle cell is termed the sarcolemma. [9] The sarcolemma receives and conducts stimuli.
Skeletal muscle cells are the individual contractile cells within a muscle, and are often termed as muscle fibers. [3] A single muscle such as the biceps in a young adult male contains around 253,000 muscle fibers. [22] Skeletal muscle fibers are multinucleated with the nuclei often referred to as myonuclei.
A myofibril (also known as a muscle fibril or sarcostyle) [1] is a basic rod-like organelle of a muscle cell. [2] Skeletal muscles are composed of long, tubular cells known as muscle fibers, and these cells contain many chains of myofibrils. [3] Each myofibril has a diameter of 1–2 micrometres. [3]
The sarcoplasmic reticulum is a network of the tubules that extend throughout muscle cells, wrapping around (but not in direct contact with) the myofibrils (contractile units of the cell). Cardiac and skeletal muscle cells contain structures called transverse tubules (T-tubules), which are extensions of the cell membrane that travel into the ...
The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual actions in the body at individual times. In addition, the glomeruli of the kidneys contain smooth muscle-like cells called mesangial cells.
These satellite cells are the main source of most muscle cell formation postnatally, with embryonic myoblasts being responsible for prenatal muscle generation. A single satellite cell can proliferate and become a larger amount of muscle cells. [28] With the understanding that myosatellite cells are the progenitor of most skeletal muscle cells ...
The fibres of striated muscle have a cylindrical shape with blunt ends, whereas those in smooth muscle are spindle-like with tapered ends. Striated muscle tissue has more mitochondria than smooth muscle. Both smooth muscle cells and cardiac muscle cells have a single nucleus, and skeletal muscle cells have many nuclei. [6]
The protein tropomyosin covers the myosin-binding sites of the actin molecules in the muscle cell. For a muscle cell to contract, tropomyosin must be moved to uncover the binding sites on the actin. Calcium ions bind with troponin C molecules (which are dispersed throughout the tropomyosin protein) and alter the structure of the tropomyosin ...