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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 .
Three distinct types of muscle (L to R): Smooth (non-striated) muscle in internal organs, cardiac or heart muscle, and skeletal muscle. There are three distinct types of muscle: skeletal muscle, cardiac or heart muscle, and smooth (non-striated) muscle. Muscles provide strength, balance, posture, movement, and heat for the body to keep warm. [3]
Smooth muscle tissue is non-striated and involuntary. Smooth muscle is found within the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and the arrector pili in the skin that control the erection of body hair.
The study of microscopic anatomy (or histology) can be aided by practical experience examining histological preparations (or slides) under a microscope; and in addition, medical and dental students generally also learn anatomy with practical experience of dissection and inspection of cadavers (dead human bodies).
The unusual microscopic anatomy of a muscle cell gave rise to its terminology. The cytoplasm in a muscle cell is termed the sarcoplasm; the smooth endoplasmic reticulum of a muscle cell is termed the sarcoplasmic reticulum; and the cell membrane in a muscle cell is termed the sarcolemma. [9]
Only skeletal and smooth muscles are part of the musculoskeletal system and only the muscles can move the body. Cardiac muscles are found in the heart and are used only to circulate blood; like the smooth muscles, these muscles are not under conscious control. Skeletal muscles are attached to bones and arranged in opposing groups around joints. [8]
Skeletal muscle is also an endocrine organ. [9] [10] [11] Under different physiological conditions, subsets of 654 different proteins as well as lipids, amino acids, metabolites and small RNAs are found in the secretome of skeletal muscles. [12] Skeletal muscles are substantially composed of multinucleated contractile muscle fibers (myocytes).
Striated muscle tissue is a muscle tissue that features repeating functional units called sarcomeres. The presence of sarcomeres manifests as a series of bands visible along the muscle fibers, which is responsible for the striated appearance observed in microscopic images of this tissue. There are two types of striated muscle: