The primary function of muscles is to facilitate movement and provide support to the body. Muscles contract and relax in response to signals from the nervous system, enabling voluntary movements like walking, running, and lifting, as well as involuntary actions such as breathing and digestion. There are three types of muscles: skeletal, cardiac, and smooth, each serving specific functions. Skeletal muscles help move bones, cardiac muscles make up the heart, and smooth muscles control movements in organs. Additionally, muscles play a role in maintaining posture and generating heat, contributing to overall bodily functions.