Breathing is the process of inhaling and exhaling air. Also called respiration, it involves the intake of air into the lungs through the nostrils and supplying oxygen to the tissues and the release of carbon dioxide. The neurological process of breathing is controlled by the brain in the medulla and the physical process is facilitated by the intercostal muscles of the chest cavity. Breathing happens as air from the higher pressure travels to an area of lower pressure. When the intercostal muscles between the ribs and the diaphragm contract, the ribcage expands thereby creating a low pressure in the lungs. Air from outside at this point enters the lungs and inhalation happens. While exhaling, the muscles of the intercostal muscles and the diaphragm relax and the ribcage contracts leading to a high pressure in the lungs. Now, air leaves the lungs leading to exhalation. In the process of breathing, oxygen enters the alveoli (air sacs present in the lungs) and enters the capillaries. The oxygen binds itself to hemoglobin in the capillaries and are carried to the heart to be supplied to each part of the body. The carbon dioxide from the tissues and cells of the body is exhaled out of the lungs. The rate at which a person inhales and exhales is called the respiration rate. It is measured per minute. Abnormal respiratory rate signifies respiratory disorders.