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Functional Properties of Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
where x denotes distance of the actin binding site from the equilibrium position of the myosin head. Cross bridges are therefore formed at a maximum rate near x = 0. The rate constants k0, k1, and k2 now depend on x under the assumed isotonic conditions. Some forms of these dependencies have to be assumed in order to solve Equations 10.10 and 10.11, analytically or numerically. Once these solutions are obtained, various quantities pertaining to muscle behavior can be derived, such as the force generated; the total energy expended, which is the sum of the heat liberated and the mechanical work performed; and the F-ʋ relation.
Skeletal Muscle
Published in Charles Paul Lambert, Physiology and Nutrition for Amateur Wrestling, 2020
Skeletal muscle contraction involves many muscle proteins as well as sodium (Na+) and potassium (K+) and adenosine triphosphate (ATP), and vital ions such as magnesium (Mg2+) and calcium (Ca2+). The whole muscle contracts by way of individual sarcomere shortening. A sarcomere is Z-line to Z-line. After the ATP is broken down, the myosin head (thick filament head) cocks, and the release of Ca2+ from the sarcoplasmic reticulum upon electrical stimulation through the T-tubule system ensures that Ca2+ binds to troponin. Once the Ca2+ binds to troponin, tropomyosin moves away from the myosin head binding site on actin. The myosin head binds and muscle contraction ensues—myosin head moving actin. The ATP then binds to the myosin head again, is split and released from actin, Ca2+ is taken back up into the sarcoplasmic reticulum and relaxation ensues, or the process of shortening continues if Ca2+ is still in the local environment.
The cardiac myocyte: excitation and contraction
Published in Neil Herring, David J. Paterson, Levick's Introduction to Cardiovascular Physiology, 2018
Neil Herring, David J. Paterson
Each actin subunit has a binding site for a myosin head, but the binding sites are blocked at rest by the ribbon-like tropomyo-sin molecule. Tropomyosin is a 42 nm-long protein that lies in the groove of the F-actin double helix, and it overlies seven G-actin subunits. Each tropomyosin has a troponin complex attached to one end, composed of three units. Troponin C is a Ca2+-binding protein; troponin I is inhibitory; and troponin T binds the complex to tropomyosin.
Myosin light chain kinase regulates intestinal permeability of mucosal homeostasis in Crohn’s disease
Published in Expert Review of Clinical Immunology, 2020
Many studies have demonstrated how MLCK directly regulates the ability of the cytoskeleton to activate the TJ barrier [48,53,54]. Ca2+/calmodulin-dependent MLCK phosphorylates the myosin RLC and activates myosin in the smooth muscle. Then, ATPase in the myosin head is activated to hydrolyze ATP, thereby converting the chemical energy to mechanical forces and motion [55]. At the same time, actin assembles to form actin filaments. Then, the heavy chain motor domain of myosin reversibly binds to actin filaments, leading to cyclic interaction between actin and myosin. With hydrolyzation of ATP (the basis of energy) and assembly of actin (the basis of structure), interaction between MLCK and skeletal proteins contributes to the interplay and contraction of skeletal proteins, finally leading to contraction of the intestinal cells [39]. With contraction of the cytoskeleton, the paracellular pathways sealed by the TJ are activated to increase intestinal permeability. Additionally, Rho-associated kinase (ROCK) has a similar role in myosin phosphorylation and activation [56].
Cross-bridge mechanism of residual force enhancement after stretching in a skeletal muscle
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2018
We assume that a local potential Hlocal(n) in the weak- and strong-binding states is provided by adenosine tri-phosphate (ATP) hydrolysis by the myosin head and the force is active in an area of ±δ (<<La = 5.7 nm) which is in one actin molecule. The local potential moves side by side with the myosin head. The force from the local potential Hlocal from Equation (5) is 2.5 pN (Finer et al. 1994; Tyska et al. 1999) in both the weak- and strong-binding states in the simulation. The force from the local potential moves the myosin head along the actin filament.