Which muscles act involuntarily?

(i) Striated muscles

(ii) Smooth muscles

(iii) Cardiac muscles

(iv) Skeletal muscles

Smooth muscles have no striations of light-dark bands and are usually found in alimentary canal, uterus, and iris of the eye. They are involuntary as they do not work according to our will. Cardiac muscles too are involuntary, present in the heart they contract and relax to pump blood.

Striated muscles and skeletal muscles have a dark and light band and are voluntary i.e. they move according to our will. They are cylindrical, un-branched and multinucleated.