Myofibrils consist of two types of protein filaments, called thin filaments and thick filaments. Troponin molecules, together with tropomyosin and actin molecules, form the thin filaments which have a helix structure - as shown in the diagram below.
Above: Diagram of troponin molecules within a thin filament
Troponin acts in combination with tropomyosin to control muscle contraction.
- During muscle relaxation, troponin holds tropomyosin in position covering myosin-binding sites on actin proteins. (The protein myosin is part of the thick filaments of muscle fibres.)
- During muscle contraction calcium ions (Ca2+) bind to troponin, changing the shape of the troponin-tropomyosin complex and therefore uncovering the myosin-binding sites on the protein actin - which is part of the thick filaments of muscle fibres.
See more about the types of muscle contraction.
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:
This section is about the
anatomical structures of muscles.
- Anterior Muscles
- Posterior Muscles
- Facial Muscles
- Muscle Terminology (Definitions)
- 1. Structure of Muscle
- 2. Structure of Muscle Cells
- 3. Muscle Filaments
- 4. Sliding Filament Theory
- 5. Neuromuscular Junction
- 6. Actions at Neuromuscular Junction
- Types of Muscle Contractions
- Muscular Disorders
- Effects of exercise on muscles