title: The origin of concepts regarding contractility, its mechanism, and its control.
abstract: The function of the heart is to contract and relax rhythmically so as to propel blood, and the requirements for that function are variable, dependent on the activity of the body. Skeletal muscle also performs variable output tasks but does so by mobilizing a smaller or larger fraction of its motor units. The heart responds in all-or-none manner and must therefore have other means of achieving variable contractile strength. In the first part of this chapter, this will be discussed in a general way, considering mechanisms that heart and muscle have in common. In the second part, we shall then examine properties that are peculiar to the myocardium. The main message of the first part is primarily that much is now known about molecular processes of contraction and of excitation--contraction coupling and that these mechanisms, although subject to specialized modifications, are common to muscle and heart. Of the second part, the main feature is that the variability of excitation--contraction coupling is a major and essential characteristic of the myocardium.
mesh_terms: D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018260:Gelsolin; D006321:Heart / Q000502:physiology*; D006801:Humans; D008840:Microfilament Proteins; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D009218:Myosins / Q000378:metabolism
chemical_list: D000199:Actins; D002352:Carrier Proteins; D018260:Gelsolin; D008840:Microfilament Proteins; C016953:brevin; D000255:Adenosine Triphosphate; D009218:Myosins