The Nervous System and Breathing

Breathing is regulated by the autonomic nervous system, specifically the medulla oblongata. The nerve cells in this centre automatically send signals to the diaphragm and intercostal muscles, making them contract at regular intervals. Another section of the brain involved in regulating breathing is the pons which has two control centres, the Apneustic centre which helps stimulate inspiration and the Pneumotaxic centre which inhibits the Apneustic centre, allowing expiration. Between these respiratory centres a regular rhythm is established so that the average person breaths 15 times per minute.

Breathing can be affected by the pH level of the blood. Chemoreceptors send signals to the medulla and this determines the depth and rate of breathing. At low pH levels the medulla becomes stimulated and this results in an increase in breathing rate. When pH levels are high there is a decrease in breathing rate due to a lack of stimulation.

Most of the time breathing is automatic, however other parts of the brain can override the medulla and pons to make breathing a conscious effort, such as when swimmers hold their breath or when breathing is controlled while meditating.

References:

http://people.hofstra.edu/sina_y_rabbany/engg81/breathingcoordination.html

www.cdli.ca/~dpower/resp/control.htm