myosin

(noun)

An albuminous body present in dead muscle formed in the process of coagulation which takes place in rigor mortis.

Related Terms

  • actin
  • sarcomere

Examples of myosin in the following topics:

  • Rigor Mortis

    • Physiologically, rigor mortis is caused a release of calcium facilitating crossbridges in the sarcomeres; the coupling between myosin and actin cannot be broken, creating a constant state of muscle contraction until enzymatic decomposition eventually removes the crossbridges.
    • Diffusion of the calcium through the pumps occurs, facilitation binding of myosin and actin filaments.
    • As part of the process of decomposition, the myosin heads are degraded by the enzymes, allowing the muscle contraction to release and the body to relax.
    • Diagram showing Actin-Myosin filaments in Smooth muscle.
    • When activated they slide over the myosin bundles causing shortening of the cell walls.
  • Microscopic Anatomy

    • The two most important proteins within sarcomeres are myosin, which forms a thick, flexible filament, and actin, which forms the thin, more rigid filament.
    • Myosin has a long, fibrous tail and a globular head, which binds to actin.
    • The myosin head also binds to ATP, which is the source of energy for muscle movement.
    • Together, myosin and actin form myofibrils, the repeating molecular structure of sarcomeres.
    • When ATP binds to myosin, it seperates from the actin of the myofibril, which causes a contraction.
  • Mechanism and Contraction Events of Cardiac Muscle Fibers

    • In the sliding filament model, myosin filaments slide along actin filaments to shorten or lengthen the muscle fiber for contraction and relaxation.
    • This removal of the troponin complex frees the actin to be bound by myosin and initiates contraction.
    • The myosin head binds to ATP and pulls the actin filaments toward the center of the sarcomere, contracting the muscle.
    • This animation shows myosin filaments (red) sliding along the actin filaments (pink) to contract a muscle cell.
  • Short-Term Chemical Control

    • The mechanism that leads to vasoconstriction results from the increased concentration of calcium (Ca2+ ions) and phosphorylated myosin within vascular smooth muscle cells.
    • The rise in intracellular calcium complexes with calmodulin, which in turn activates myosin light chain kinase.
    • This enzyme is responsible for phosphorylating the light chain of myosin to stimulate cross bridge cycling.
    • As with vasoconstriction vasodilation is modulated by calcium ion concentration and myosin phosphorylation within vascular smooth muscle cells.
    • Dephosphorylation by myosin light-chain phosphatase and induction of calcium symportersand antiporters that pump calcium ions out of the intracellular compartment both contribute to smooth muscle cell relaxation and therefore vasodilation.
  • Overview of Motor Integration

  • Force of Muscle Contraction

    • When a sarcomere contracts, myosin heads attach to actin to form cross-bridges.
    • Simply put,  the tension generated in skeletal muscle is a function of the magnitude of overlap between actin and myosin myofilaments.
    • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
  • Myocardial Thickness and Function

    • Two of the important proteins found in sarcomeres are myosin, which forms the thick filament, and actin, which forms the thin filament.
    • Myosin has a long, fibrous tail and a globular head, which binds to actin.
    • The myosin head also binds to ATP, which is the source of energy for cellular metabolism, and is required for the cardiomyocytes to sustain themselves and function normally.
    • Together, myosin and actin form myofibril filaments, which are the elongated, contractile threads found in muscle tissue.
  • Velocity and Duration of Muscle Contraction

    • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
  • Myocarditis and Endocarditis

    • Streptococcal M protein and coxsackievirus B have regions (epitopes) that are immunologically similar to cardiac myosin.
    • After the virus is gone, the immune system may attack cardiac myosin.
  • Exercise-Induced Muscle Damage

    • Delayed onset muscle soreness is caused by structural damage to the Z disk and myosin and actin filaments.
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