Muscular system: It is system that consists of skeletal, smooth and cardiac muscles. It plays an important role in maintaining posture, controlling body movement, and blood circulation throughout the body. The muscular system in vertebrates is controlled by the nervous system but certain muscles such as the cardiac muscle can be completely autonomous There are three different types of muscles namely- skeletal muscles or striated muscles, cardiac or heart muscles, and smooth or non-striated muscles. Muscles provide strength, balance, posture, controls movement and heat for the body to keep it warm. Skeletal muscles or voluntary muscles can be controlled by conscious thought. For example voluntary movement of hands, legs etc. There are approximately 639 skeletal muscles in the human body. Smooth muscles are directly controlled by the autonomic nervous system and are involuntary, which means that they are incapable of being moved by conscious thought. Functions such as heart beat and breathing, which are capable of being willingly controlled through a limited extent are involuntary muscles but are not smooth muscles. Heart muscles are different from skeletal muscles because the muscle fibers are laterally connected to each other. Heart muscles are controlled by the sinus node influenced by the autonomic nervous system.