The mechanism of breathing is controlled by nerve cells in the parts of the brainstem known as the medulla oblongata and the pons varioli. Together these nerve cells are often referred to as the respiratory centre, although there is no clearly defined group of cells that can be identified as controlling respiration.

These cells send impulses down the spinal cord and then via the phrenic nerve to the diaphragm and via the intercostal nerves to the muscles of the rib cage.

An inbuilt rhythmical pattern of activity maintains regular movements of the muscles that control breathing. This pattern can be altered by pain, exercise and conscious effort.

During exercise, nerve impulses from exercising limbs are transmitted to the brainstem and cause an increase in the rate and depth of breathing.