Dynamics of smooth muscle contraction

Smooth muscle can economically maintain tonus for a long time and in many organs, its purpose is to maintain organ dimensions. It is however relatively slow and also inefficient as far as mechanical work is concerned. Smooth muscle is found in the majority of organs in the human body. It is characterized by an abundant functional diversity associated with many regulatory systems in combination with, most likely, a common intracellular contractile apparatus. The regulatory systems involve different neurotransmitters, hormones, ions, metabolites, and responses mediated by other associated cells and nerves. In the urinary bladder a special kind of smooth muscle has evolved in which the maintenance of tonus is less important than the generation of mechanical work necessary to evacuate mine. In the major palt of its cycle, the filling phase, the muscle is in the relaxed state, and it only develops force for a relatively short period during micturition. In this way the function of it closely resembles that of skeletal muscle.