has_participant has participant muscle contraction smooth muscle contraction visceral muscle contraction GO:0006939 biological_process A process in which force is generated within smooth muscle tissue, resulting in a change in muscle geometry. Force generation involves a chemo-mechanical energy conversion step that is carried out by the actin/myosin complex activity, which generates force through ATP hydrolysis. Smooth muscle differs from striated muscle in the much higher actin/myosin ratio, the absence of conspicuous sarcomeres and the ability to contract to a much smaller fraction of its resting length. muscarinic acetylcholine receptor M3 (human) 5-hydroxytryptamine receptor 2A (human) 5-hydroxytryptamine receptor 7 (human) alpha-1A adrenergic receptor (human) 5-hydroxytryptamine receptor 2B (human)