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Muscles are made up of hundreds of thousands of muscle cells (also called muscle fibres). These muscle cells act together to perform the functions of the specific muscle they are part of.
Unlike other tissue, muscle cells contain myofibrils – these are shaped like long cylinders and extend along the full length of the muscle fibre/cell.
Each myofibril consists of two types of protein filaments called thick filaments and thin filaments. The thick filaments and the thin filaments within myofibrils overlap, and the sections where they overlap and occur together are called sarcomeres. When muscle contraction occurs, the thin filaments and the thick filaments slide past each other.