AP PSYCHOLOGY

Detailed explanation-1: -Smooth muscle, found in the walls of the hollow internal organs such as blood vessels, the gastrointestinal tract, bladder, and uterus, is under control of the autonomic nervous system. Smooth muscle cannot be controlled consciously and thus acts involuntarily.

Detailed explanation-2: -(i) Muscles of iris and ciliary body are smooth muscles of mesodermal origin. (ii) Slow and sustained involuntary contraction of smooth muscles are called spasms. (iii) Quiescent mononucleate myogenic cells of skeletal muscles are called pericytes.

Detailed explanation-3: -Because there are no striations when viewed under a microscope, involuntary muscles are also known as smooth muscles or non-striated muscles. Complete answer: Smooth muscles can be found in the oesophagus, stomach, intestine, blood vessels, iris of the eye, and dermis of the skin.

Detailed explanation-4: -Smooth muscle cells are spindle shaped, have a single, centrally located nucleus, and lack striations. They are called involuntary muscles. Cardiac muscle has branching fibers, one nucleus per cell, striations, and intercalated disks. Its contraction is not under voluntary control.