Thick Filament

A thick filament is one of the two types of protein filaments that, together form cylindrical structures call myofibrils which extend along the length of muscle fibres. The other type of protein filament that is found in myofibrils is called a thin filament.

Thick filaments are formed from a proteins called myosin grouped in bundles as shown below.

Above: Labelled diagram of a thick filament

The myosin molecules are arranged in a bipolar structure within thick filaments. Their protruding club-like heads point towards the ends of the thick filaments while their shafts lie towards the middle. Therefore each thick filament has a central, bare, zone and an array of protruding heads of opposite polarity at each end.

Thick filaments are typically 130 nm long and 12 to 15 nm in diameter. (There are 1,000,000,000 nm in a metre, or 1,000,000 nm in one mm.)

Thick filaments self-assemble in vitro under the right ionic conditions.


See more aboutalso the structures of muscle filaments.


This section consists of short summaries about the structures that form the muscles of the body. This list is not exhaustive but is intended to be appropriate for students of A-Level Human Biology, ITEC courses in massage and related subjects, and other courses in health sciences. For more general information about muscles see the pages about:

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