Smooth Muscle

Smooth muscle cells do not exhibit striations, due to a less orderly myofilament arrangement. It occurs as bundles or sheets, with elongated fusiform cells with finaled tapered ends. They range in length from 20μm small blood vessel walls to 200μm in the gut wall. May be as large as 500μm in the uterine wall during pregnancy. Interconnected by gap junctions.

• Nuclei are in the center of the cell, often having a corkscrew appearance in longitudinal sections (due to contraction during fixation - corkscrew nucleus aids in distinguishing muscle cells from fibroblasts). Obliquely arranged actin filaments are visible in the cytoplasm called dense bodies.
• Smooth muscle is found in the muscles of the iris, viscera, skin of the scrotum, vascular system, arrector pili muscles of the skin, and dartos muscles. It is also the intrinsic muscle of the gut, blood vessels, genitourinary tract, respiratory tract, and other hollow or tubular organs.