myofibrillerne

Myofibrils are the fundamental contractile units of muscle cells, also known as muscle fibers. These long, cylindrical organelles are packed tightly within the sarcoplasm of a muscle cell and are responsible for generating the force that allows muscles to contract and move the body. Each myofibril is composed of a series of repeating subunits called sarcomeres.

Sarcomeres are the smallest functional units of a myofibril and are characterized by their highly organized arrangement of protein filaments. The two main types of protein filaments involved are actin and myosin. Actin filaments are thin and extend from the edges of the sarcomere towards the center, while myosin filaments are thicker and are located in the center, overlapping with the actin filaments. The alternating arrangement of these filaments, along with associated proteins like troponin and tropomyosin, creates the characteristic striated appearance of skeletal muscle tissue.

The process of muscle contraction, known as the sliding filament theory, involves the myosin filaments pulling the actin filaments towards the center of the sarcomere. This sliding action shortens the sarcomere, and since myofibrils are made up of thousands of sarcomeres arranged in series, the overall shortening of the myofibril and thus the muscle fiber occurs. This mechanical event, triggered by a nerve impulse and the release of calcium ions, is the basis of all voluntary and involuntary muscle movements.