stuff for biology coz well i blog more than i read emails !

Function

Smooth muscle thus subserves all internal, involuntary functions, except the movements of breathing and the beating of the heart. Many directly acting chemical agents affect its contraction, but most smooth muscle is also under the control of the autonomic nervous system; in some sites (notably most blood vessels) it is influenced only by the sympathetic component, and at others (for example in the gut and the iris) by dual, and sometimes opposite, effects of sympathetic and parasympathetic nerves.

As befits its many functions, smooth muscle at different sites is much more heterogeneous than skeletal or cardiac muscle. By creating diverse structural arrangements of smooth muscle and other associated cells, and at the same time varying the mechanisms that control contraction, evolution has achieved a remarkable diversity of smooth muscle-containing organs, each of which is designed to fill a unique functional niche.