The key components for muscle contraction are the protein filaments Myosin and Actin. These filaments are found within the myofibrils which are an arrangement of separate units (sarcomeres) connected end on to form long strands.
This arrangement is shown in the diagrams below.
A muscle cell contains many parallel myofibrils and the sarcomere typically repeats every 2.3 μm along the fibril axis in relaxed muscle.
This diagram shows sarcomeres and myofibril bands
The thick filaments (15nm diameter) found in the H-zone consist primarily of myosin. the thin filaments (9nm diameter) found in the I-band consist of actin as well as tropomyosin and the troponin complex.
Last updated by Andrew Robinson 26th May 2004