vöðvatrefjur
Vöðvatrefjur, also known as muscle fibers, are the fundamental cellular units of muscle tissue in vertebrates and invertebrates. These elongated cells are specialized for contraction, enabling movement. In skeletal muscle, vöðvatrefjur are long, multinucleated cells that appear striated under a microscope due to the organized arrangement of contractile proteins actin and myosin. Smooth muscle fibers are typically spindle-shaped, uninucleated, and lack striations, found in the walls of internal organs. Cardiac muscle fibers, found in the heart, are branched, striated, and generally uninucleated, connected by intercalated discs.
The contraction of vöðvatrefjur is triggered by a nerve impulse or hormonal signals. This signal initiates