Smooth (Non-Striated) Muscles

Smooth or non-striated muscles occur in the form of sheets or layers rather than as discrete bundles. Each muscle cell is spindle-shaped (fusiform), unbranched, and carries a single nucleus at its centre. The sarcoplasm contains myofibrils built, as in other muscle, from the contractile proteins actin and myosin — but smooth muscle contains comparatively less myosin and more actin than skeletal muscle, and it shows no striations.

Smooth muscle undergoes slow, sustained, involuntary contractions, and is innervated by the autonomic nervous system rather than by voluntary motor nerves. …