Respiratory mechanism is controlled by central nervous system. Respiratory movements are under the control of Medulla oblongata, which is the breathing centre. In fact, breathing is controlled by pneumotoxic and apneustic centres in pons varolii and expiratory and inspiratory centres in Medulla oblongata. Medullary respiratory centre is constantly under direct chemical control. The respiratory centre leads to faster breathing on account of arterial blood entering the respiratory centre. It is also to be noted that impulse for voluntary forced breathing starts in cerebral hemisphere. Cerebellum contains centres for involuntary muscular coordination. Hypothalamus regulate body temperature, called, thermostat of the body. Pericardium is the membrane surrounding the heart, known as pericardial sac.