1. Axon 2. Motor end plate 3. Muscular fiber 4. Myofibril
Myofibrils, also called contractile elements, are part of the cytoskeleton. They are made up of long threaded protein chains of the proteins myosin and actin. These protein chains are also called actin and myosin filaments due to their wire form.
In combination with actin filaments, they have several functions in the movements of cells; In this way, calcium ions stimulate the myosin spoons to attach to a parallel actin filament, thus sliding the filaments apart. This principle is widely used in muscle fibers, in the removal of vesicles within the cell and in the cleavage of animal cells during mitosis and meiosis.
Light-microscopic views show a relaxed myofibril alternately dark bands called the A tires and light tires called I tires. The A tires mainly contain myosin, the I tires on the other hand contain mainly actin. Each I band is divided into two by a disk of proteins. This disk is called the Z-line. The tires of all myofibrils lie parallel to each other, giving the muscles the striped appearance. The thin actin filaments partially extend into the thick myosin filaments on both sides of the A band. If the muscle is at rest, this will not be all the way to the middle of the A-band. As a result, the A-band in the middle is slightly lighter than on both sides of the center. This band has been named H-band. The part of Z-line to Z-line, between which twice a part I-band and a whole A-band is called a sarcomaer. Numerous myofibrils together form a muscle fiber.
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