Muscle tissue is one of the four main tissue types in the human body. It comprises cells with the remarkable ability to contract to perform various physiological functions. Muscles are of three types — skeletal, cardiac, and smooth muscles. Skeletal muscles are striated and are indirectly attached to bones. They can be voluntarily controlled to move body parts, such as the arms or legs. These muscles also help maintain body posture. For instance, the neck muscles aid in holding the head upright. Cardiac muscles are found exclusively in the heart. Although striated, they function involuntarily and are autorhythmic — meaning they are not entirely dependent on neural signals for contractions. This rhythmic contraction functions to pump blood through the cardiovascular system. The third type, smooth muscles, are found lining the hollow visceral organs and blood vessels. They are non-striated, involuntary muscles that control the passage of substances through the body, for instance, the movement of food through the esophagus. Additionally, all muscles, especially skeletal muscles, contribute significantly to maintaining normal body temperature by generating heat during contractions.