Question

Unstriated muscles are found in
A. Veins
B. Arteries
C. Uterus
D. All of the above

Answer 1

Hint: Unstriated muscles consist of long and narrow cells having a single centrally placed nucleus. The cells are spindle-shaped and have no branches. They are generally smooth muscles that line almost all internal organs except the heart. They are involuntarily controlled. The contractions are automatic.

Complete answer: The unstriated muscles are smooth muscles that are present as the inner lining of almost all internal organs except for the heart. The cells that make up the unstriated muscle are long and narrow having no striations. The cells are unbranched and so give a smooth appearance. The spindle-shaped cells make up the layers or sheets that contract without conscious control. These muscles work involuntarily. They are capable of slow rhythmic contractions. The unstriated muscles are made up of cross-bridges between actin and myosin filaments. These filaments are very thin and are arranged randomly giving a smooth appearance with no striations. This means that unstriated muscles lack stripes. The contractility of the digestive tract, urinary bladder, reproductive system, airways, and blood vessels are attributed to the contractions derived by unstriated muscles. The autonomous nervous system controls their working. Due to this reason, they are also called involuntary muscles. Also, they store less amount of glycogen as they have a lesser amount of mitochondria present in them as compared to striated muscles. Thus, veins, arteries, and uterus, all consist of unstriated muscles that line them and help in their contraction.
Hence, the correct answer is option D.

Note: Unstriated muscle cells are seen as irregular in shape due to poorly developed contractile elements. The cells are although long but are not cylindrical. They are always uni-nucleated. They have poorly developed sarcoplasmic reticulum in them. Unlike striated muscles, the unstriated muscles are not joined by tendons.