Muscle contraction, physiology

A. Horowitz, C. B. Menice, R. Laporte, and K. G. Morgan Mechanisms of smooth muscle contraction. Physiological Reviews 76,967 (1996). 

Biological functions of Ca(Il) ion are numerous but maybe classified ia one of three categories the formation of soHd skeletal material such as bone, teeth, and shell the stabilizing of proteia conformational stmcture and the most varied, the abiUty of Ca(Il) to trigger certain physiological activities such as muscle contraction and the release of hormones (qv). 

Smooth muscle contractions are subject to the actions of hormones and related agents. As shown in Figure 17.32, binding of the hormone epinephrine to smooth muscle receptors activates an intracellular adenylyl cyclase reaction that produces cyclic AMP (cAMP). The cAMP serves to activate a protein kinase that phosphorylates the myosin light chain kinase. The phosphorylated MLCK has a lower affinity for the Ca -calmodulin complex and thus is physiologically inactive. Reversal of this inactivation occurs via myosin light chain kinase phosphatase. 

The Ca2+-binding subunit TN-C is homologous to calmodulin with four EF-hands. In contrast to calmodulin, which is ubiquitously expressed in multicellular eukaryotic organisms and interacts with many targets, troponin specifically regulates muscle contraction. There are some structural differences between Troponin C in skeletal and cardiac muscles reflecting their physiological differences. 

Bigland-Ritchie, B. (1981). EMG and fatigue of human voluntary and stimulated contractions. In Human Muscle Fatigue Physiological Mechanisms (Porter, R. Whelan, J., eds.), pp. 130-156. Pitman, London. 

Papanek, P.E., Exercise physiology and the bioenergetics of muscle contraction, in Physiology Secrets, Raff, H., Ed., Hanley and Belfus, Inc., Philadelphia, 1999, chap. 8. 

Another reductionist fallacy is the claim that a biochemical process can cause a physiological process. As pointed out by Rose (1998) a biochemical reaction such as the interaction between actin and myosin is not the cause of a physiological event such as muscle contraction. The biochemical process does not precede muscle contraction and therefore cannot cause it ... 

Like nitric oxide, the discovery of the eicosanoid signalling molecules was a significant event in twentieth century physiology, due largely to research led by Sir John Vane (Nobel Prize 1982). The diverse actions of the eicosanoids include roles in muscle contraction, blood coagulation, salt and fluid homeostasis, inflammatory responses and pain sensitivity. 

Muscle spindles are composed of nuclear bag (dynamic) and chain (static) fibres known as intrafusal fibres and these are innervated by y motor neurones. Extrafusal fibres make up the muscle bulk and are innervated by a motor neurones. Stimulation of the muscle spindle leads to increased skeletal muscle contraction, which opposes the initial stretch and maintains the length of the fibre. This feedback loop oscillates at 10 Hz, which is the frequency of a physiological tremor. 

Calcium is the principal extracellular electrolyte regulated by PTH, calcitonin, and D3. Extracellular calcium is a critical component of signal transduction across the plasma membrane, which regulates a wide spectrum of physiological events including muscle contraction, secretion of neurotransmitters and hormones, and the ac-... 

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