Smooth Muscle – Tutorial

Please read Unit 4 – Introduction to Muscle Tissue prior to completing the activities in this chapter.

Introduction to Smooth Muscle

Smooth muscle tissue consists of small, spindle-shaped (kayak-shaped) cells with a single, centrally located nucleus.  Unlike cardiac and skeletal muscle cells, smooth muscle cells do not exhibit striations since their actin and myosin (thin and thick) protein filaments are not organized as sarcomeres.  Smooth muscle cells are under involuntary (autonomic) control and usually organized into functional sheets, layers, or bands of hundreds to thousands of cells in the walls of blood vessels and tube-like organs of the digestive, reproductive, urinary, and lower respiratory tracts.   Smooth muscle provides mechanical support for the walls of tube-like organs and controls important functions such as peristalsis, dilation/constriction, and regulation of sphincter activity.  Smooth muscle cells also comprise arrector pili muscles in the dermis of skin and are found in the iris and ciliary body of the eye.

Smooth muscle is typically arranged in longitudinal and circular layers in the walls of visceral tube-like organs which produce peristaltic contractions capable of moving contents along the lumen of the digestive, reproductive, and urinary tracts.  Circular bands of smooth muscle in the walls of blood vessels and bronchioles of the respiratory tract regulate lumen diameter by relaxing to dilate and contracting to constrict.  Although contraction of individual smooth muscle cells in the iris of the eye and walls of large arteries is stimulated directly by neurons, contraction of smooth muscle in most other locations is stimulated by action potentials that spread from cell to cell through gap junctions along functional layers or sheets of thousands of adjacent smooth muscle cells.  Waves of spreading smooth muscle contractions are responsible for peristalsis of tube-like visceral organs.  It should also be noted that smooth muscle cells can contract or relax in response to a variety of non-neurological stimuli such as excessive stretching, hormonal stimulation, stimulation by inflammatory chemicals, or changes in local temperature and/or concentration of O₂ and CO₂.

Tutorial:  Use the image slider below to learn more about the characteristics of smooth muscle tissue. 

Microscopy:  Use the image slider below to learn how to use a microscope to study smooth muscle tissue on a microscope slide of the small intestine.

Tutorial:  Use the hotspot image below to learn more about the characteristics of smooth muscle tissue. 

Tutorial:  Use the image slider below to study numerous examples of smooth muscle tissue.