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Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle. Most smooth muscle is of the single-unit type, and is found in the walls of most internal organs (viscera); and lines blood vessels (except large elastic arteries), the urinary tract , and the digestive tract .
The majority of this type of muscle tissue is found in the digestive and urinary systems where it acts by propelling forward food, chyme, and feces in the former and urine in the latter. Other places smooth muscle can be found are within the uterus, where it helps facilitate birth, and the eye, where the pupillary sphincter controls pupil size. [3]
The muscular system is an organ system consisting of skeletal, smooth, and cardiac muscle. It permits movement of the body, maintains posture, and circulates blood throughout the body. [ 1 ] The muscular systems in vertebrates are controlled through the nervous system although some muscles (such as the cardiac muscle ) can be completely autonomous.
Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the voluntary muscular system [ 1 ] and typically are attached by tendons to bones of a skeleton .
Cardiac muscle tissue is found only in the walls of the heart as myocardium, and it is an involuntary muscle controlled by the autonomic nervous system. Cardiac muscle tissue is striated like skeletal muscle, containing sarcomeres in highly regular arrangements of bundles.
Unlike skeletal and cardiac muscle tissue, smooth muscle tissue is not striated since there are no sarcomeres present. Skeletal muscles are attached to some component of the skeleton, and smooth muscle is found in hollow structures such as the walls of intestines or blood vessels. The fibres of striated muscle have a cylindrical shape with ...
In the skin, smooth muscle cells such as those of the arrector pili cause hair to stand erect in response to cold temperature or fear. [19] Smooth muscle cells are spindle-shaped with wide middles, and tapering ends. They have a single nucleus and range from 30 to 200 micrometers in length. This is thousands of times shorter than skeletal ...
In the upper esophagus, part of the externa is skeletal muscle, rather than smooth muscle. In the vas deferens of the spermatic cord, there are three layers: inner longitudinal, middle circular, and outer longitudinal. In the ureter, the smooth muscle orientation is opposite that of the GI tract. There is an inner longitudinal and an outer ...