Myofibril

A Muskelfibrille, also called myofibril is in the muscle ( muscle fibers), a functional unit at the level of Zellorganells, which enables the cell an active shortening ( contraction).

Muscle fibers form Muskelfibrillenbündel

Many muscle fibers are grouped within the muscle fiber by the intermediate filament desmin to fibrils, which are wound by a special expression of the endoplasmic reticulum, the sarcoplasmic reticulum.

A Muskelfibrille consists of sarcomeres

A Muskelfibrille consists of hundreds of series-connected units with the same internal structure, the sarcomeres. If one considers a Muskelfibrille with the light microscope, a typical cross-striation is visible, which is caused by the regular distribution of Muskelfilamente. The result is a typical band pattern.

The sarcomeres consist mainly of parallel arranged thick protein fibers, the myosin. Between the myosin filaments protrude the thinner actin filaments. The whole complex is stabilized by Titin, the largest protein of the human body. α - actinin is periodically fixed Anheftungsscheiben which give thin titin filaments. Are the myosin molecules between these threads. Their ends overlap with the ends of actin fibers.

The Muskelfibrille shortened by Filamentgleiten

In a contraction, calcium ions are released from the sarcoplasmic reticulum, which diffuse between the myosin and actin filaments. The calcium ion (Ca2 ) trigger interactions between the myosin and actin filaments, so that the actin filaments between the myosin filaments slide ( Gleitfilament mechanism of muscle contraction ). Thus, the single sarcomere and with this all muscle fibers of a muscle fiber shortens. The muscle fiber twitches. The shortening of many muscle fibers leads to forceful contraction of the muscle.