Sarcomere

Muscles are responsible for making movements through muscle contractions. Muscles consist of many different fibers, which consist of myofibrills. Myofibrills in turn consist of many sarcomeres in series. A sarcomere is the smallest functional unit in a muscle and is the structure that makes the muscle contraction possible.

A sarcomere consists of thin actin filaments and thick myosine filaments, which can slide past each other when the sarcomere contracts. The actin filaments are connected to the z-lines which form the connections between the sarcomeres in series. The myosin filaments are in the middle of the sarcomere in the center of several actin filaments. Each myosin filament has myosinheads portruding from the filament, which can bind to special binding places on the actin filaments. Through this interaction between actin and myosin filaments, sarcomeres are able to exert force.

When a contraction is started, the myosin heads are activated and form so called cross-bridges by binding at the binding places at the actin filaments. After forming the cross-bridge, the myosinhead pulls at the actin filament, and the filaments slide past each other, shortening the sarcomere. After this, the myosinhead unbinds and returns to its original position, ready to form another crossbridge with the next binding place.Muscle structure

References:

-Wilmore, J.H., Costill, D.L., Kenney, W.L. (2008). Structure and function of exercising muscle. Physiology of Sport and Exercise Fourth Edition. USA Human Kinetics.