Also found in: Dictionary
filament (fil′ă-mĕnt) [L. filamentum, threading]
1. A fine thread.
2. A threadlike coil of tungsten found in the x-ray tube that is the source of electrons.
A filament forming the central axis of the flagellum of a spermatozoon.
intermediate filament Abbreviation: IF
Slender proteins found in all eukaryotic cells, measuring about 8 to 12 nm in diameter. Intermediate filaments are composed of proteins including desmin, keratins, lamins, and vimentin and together with microtubules and microfilaments form the cytoskeleton. Some malignant cells can be identified by the specific proteins in their intermediate filaments.
Myosin, seen microscopically.
Actin, seen microscopically.
thick filaments The myosin filaments in muscle cells.
Figure 1: The nervous system.
myofibrils longitudinally oriented cytoplasmic components of skeletal and cardiac muscle fibres, which are the loci of force-generation when the muscle is activated. Each myofibril extends the whole length of the fibre though it is typically only ∼1 μm diameter; thus a fibre of 100 μm diameter has several thousand fibrils in its cross-section. In turn, each fibril is composed of numerous parallel filaments of myofibrillar proteins, chiefly myosin in thick filaments and chiefly actin in thin filaments, alternating and partially overlapping along the length of each myofibril, and so giving rise to the cross-banding pattern of the lengthwise repeating sarcomeres; these are aligned side by side across the fibre, giving it (under appropriate histological stains or optical imaging techniques) the striated appearance characteristic of these two classes of muscle. Interaction between the two proteins, myosin and actin, at the cross-bridges results in the generation of active force during muscle contraction. See also sarcoplasmic reticulum; Figure 1.
myosin one of the two main myofibrillar proteins in the myofibrils of a muscle fibre. A dimeric molecule comprising two identical monomers. Each monomer consists of a long chain ('light meromyosin, LMM') which readily associates with the chains of other myosin molecules to form the thick filaments, and a more globular component ('heavy meromyosin, HMM'), itself further divisible into two subunits, S2 and S1. The latter are the myosin head-groups, embodying an ATPase and an actin-binding site; it is these that interact with actin in the thin filaments when the muscle is activated, to form the force-generating (actin-myosin) cross-bridges. This whole monomer constitutes one myosin heavy chain (MHC). However, associated with the head-groups are two myosin light chains (MLC), of uncertain function. (Since myosin is not the only constituent of thick filaments, the term 'myosin filament' is a misnomer and better avoided). See also muscle contraction, sliding filament theory.