Myoblast

A myoblast is a type of embryonic progenitor cell that gives rise to muscle cells (myocytes).

The muscle cells can be skeletal muscle, smooth muscle, and cardiac muscle.

Skeletal muscle fibers are made when myoblasts fuse together; muscle fibers therefore have multiple nuclei (each nucleus originating from a single myoblast). The fusion of myoblasts is specific to skeletal muscle (example: biceps) and not cardiac muscle or smooth muscle.

Within the muscle fiber (myocyte), there are bundles of myofibrils which are composed of a series of sarcomeres. Sarcomeres are the basic contractile units which consist of thin and thick filaments. Thin filaments are actin filaments and thick filaments consist of an arrangement of myosin proteins. The sarcomere does not contain organelles or a nucleus.

Myoblasts that do not form muscle fibers dedifferentiate back into satellite cells. These satellite cells remain adjacent to a muscle fiber, situated between the sarcolemma and the endomysium (the connective tissue investment that divides the muscle fascicles into individual fibers).