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Skeletal muscles are composed of tubular muscle cells (called muscle fibers or myofibers) which are formed during embryonic myogenesis. Muscle fibers contain numerous tubular myofibrils . Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as alternating dark and light bands.
Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle. Most smooth muscle is of the single-unit type, and is found in the walls of most internal organs (viscera); and lines blood vessels (except large elastic arteries), the urinary tract , and the digestive tract .
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]
Smooth muscle cells are so-called because they have neither myofibrils nor sarcomeres and therefore no striations. They are found in the walls of hollow organs , including the stomach , intestines , bladder and uterus , in the walls of blood vessels , and in the tracts of the respiratory , urinary , and reproductive systems .
Striated muscle tissue is a muscle tissue that features repeating functional units called sarcomeres. The presence of sarcomeres manifests as a series of bands visible along the muscle fibers, which is responsible for the striated appearance observed in microscopic images of this tissue.
Finally, the muscle fibers that form later arise from satellite cells. [3] Two genes significant in muscle fusion are Mef2 and the twist transcription factor. Studies have shown knockouts for Mef2C in mice lead to muscle defects in cardiac and smooth muscle development, particularly in fusion. [13] The twist gene plays a role in muscle ...
Although smooth muscles do not form regular arrays of thick and thin filaments like the sarcomeres of striated muscles, contraction is still due to the same sliding filament mechanism controlled by myosin crossbridges interacting with actin filaments. The thin filament of smooth muscle is made of actin, tropomyosin, caldesmon, and calmodulin ...
The costamere is a structural-functional component of striated muscle cells [1] which connects the sarcomere of the muscle to the cell membrane (i.e. the sarcolemma). [2] Costameres are sub-sarcolemmal protein assemblies circumferentially aligned in register with the Z-disk of peripheral myofibrils.