Enkephalin primarily contracts which type of muscle?

Enkephalins are neuropeptides that play a significant role in modulating pain and creating feelings of well-being. They primarily act on the body's opiate receptors in the central nervous system and the peripheral nervous system. When it comes to muscle contraction, enkephalins have a notable effect on smooth muscle.

Smooth muscle is found in various structures throughout the body, including the walls of blood vessels, the gastrointestinal tract, and other internal organs. Enkephalins are involved in processes such as vasodilation and gut motility, suggesting their role in inhibiting smooth muscle contraction under certain conditions. Therefore, enkephalins primarily act on smooth muscle rather than skeletal or cardiac muscle types.

While skeletal muscle is under voluntary control, and cardiac muscle is specialized for rhythmic contraction, the action of enkephalins is more aligned with the involuntary regulation of smooth muscle activity, making this the correct choice.