The physiological control of respiration originates from neurons in the medulla and pons. The medulla signals the muscles involved in breathing, and the pons control the breathing rate. Together, these respiratory centers regulate the involuntary control of respiration, whereas the cerebral cortex allows voluntary control of breathing. The most vital respiratory stimulant is carbon dioxide. It causes an increase in respiratory depth and rate. Chemoreceptors monitor arterial blood for changes in the pH and partial pressure of carbon dioxide and oxygen and communicate to the medulla to send nerve impulses to respiratory muscles. From the spinal cord, the phrenic, vagus, and posterior thoracic nerves signal the ascending respiratory pathway to stimulate the diaphragm and intercostal muscles. The function of these muscles involves facilitating ventilation by inducing volume and pressure alterations within the respiratory system. As a result, this conscious effort of ventilation aids in eliminating excess carbon dioxide while simultaneously boosting oxygen levels within the body.