Why are voluntary muscles called striated muscles?

Voluntary muscles are called striated muscles because of their microscopic appearance. Under a microscope, these muscles exhibit a striped or striated pattern. This striation is caused by the arrangement of contractile proteins within the muscle fibers.

Striated muscles are composed of long, multinucleated fibers, each containing bundles of contractile proteins called myofibrils. These myofibrils are further composed of repeating units called sarcomeres. Within the sarcomere, there are alternating bands of light and dark regions, giving the muscle fibers a striped appearance. These bands are created by the overlapping arrangement of the two main types of contractile proteins: actin (thin filaments) and myosin (thick filaments).

The precise alignment and interaction of actin and myosin filaments during muscle contraction give rise to the striated pattern observed microscopically. The striations are particularly prominent in skeletal muscles, which are under voluntary control, hence the term "voluntary muscles" being synonymous with "striated muscles." However, it's worth noting that not all striated muscles are under voluntary control; for instance, cardiac muscle, found in the heart, is also striated but operates involuntarily.