In fact the regulation of actomyosin formation occurs at the myosin of the thick filament in a very different fashion from that described earlier. The myosin is now activated and can form actomyosin complexes and produce force and shortening in the usual fashion. This Phosphatase dephosphorylates the myosin site and returns it to the inactive state, resulting in relaxation. There are three general physiological characteristics that apply across all categories of smooth muscle. They are capable of slow sustained contractions maintained with a minimum energy expenditure.
Motor innervation is exclusively via the autonomic nervous system.
This activity spreads throughout the muscle as if it were a single unit, hence the name unitary smooth muscle. In this sense it is analogous to cardiac muscle in that it behaves as a syncytium. In addition unitary muscle responds to stretch with an active contraction. Examples of organs containing unitary smooth muscle are the G.I. tract, the uterus, and the ureter. Multi-unit smooth muscle does not contract spontaneously, contraction must be initiated by neuronal activation through a neuromuscular junction.