What are the three main types of muscles?

The three main types of muscles are skeletal, smooth, and cardiac. Skeletal muscle is the type of muscle that connects to bones and is responsible for voluntary movements and locomotion. It is striated in appearance and can be controlled consciously. Smooth muscle, found in the walls of hollow organs such as the intestines and blood vessels, operates involuntarily and is non-striated, aiding in processes like digestion and regulation of blood flow. Cardiac muscle is specific to the heart and is also involuntary, striated, and has unique intercalated discs that allow for rapid communication between muscle cells to ensure effective heart contractions.

The other options contain elements that do not fit the classification of muscle types. Epithelial tissue is not a muscle type but rather a category of tissue that covers body surfaces and lines cavities. Additionally, the terms "visceral" and "multiunit" pertain to degrees of smooth muscle classification but do not represent distinct types of muscle on their own. Thus, the correct identification of the three main types of muscles is critical for understanding the different functions and characteristics within the muscular system.