Smooth muscle

Smooth muscle is muscle inside the body and not attached to bones. It is not under conscious control. Its function is to help the inner workings of the body.

Smooth muscle is found in the walls of blood vessels, vessels of the lymphatic system, the urinary bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, most ducts, and a number of other places such as the iris.

The smooth muscle looks different from the skeletal muscle, and works differently. It can squeeze slowly, and move in waves along a duct. Most types of smooth muscle squeeze gently for a long time, and use little energy. Some smooth muscle squeezes quickly and relaxes in phases.

Smooth Muscle Media

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  Smooth muscle tissue, highlighting the inner circular layer (nuclei then rest of cells in pink), outer longitudinal layer (nuclei then rest of cells), then the serous membrane facing the lumen of the peritoneal cavity

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  The dense bodies and intermediate filaments are networked through the sarcoplasm, which cause the muscle fiber to contract.

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  A series of axon-like swellings, called varicosities from autonomic neurons, loosely form motor units through the smooth muscle.

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  Diagram showing Actin-Myosin filaments in Smooth muscle. The actin fibers attach to the cell wall and to dense bodies in the cytoplasm. When activated they slide over the myosin bundles causing shortening of the cell walls