9.4 Control of Breathing

Notes

Breathing is controlled by respiratory centers in the medulla oblongata (sets the basic rhythm) and pons (smooths the rhythm).

• The main stimulus is the level of carbon dioxide (as it affects pH) in the blood and brain fluid, detected by chemoreceptors. Rising CO2 lowers pH and increases the breathing rate and depth. Low oxygen can also stimulate breathing, but it is a weaker stimulus unless it falls dramatically.
• Voluntary control by the cerebral cortex is limited: you cannot hold your breath until you die, since rising CO2 forces breathing.
• Hyperventilation blows off CO2, raising pH, and may cause dizziness. Hypoventilation raises CO2.
• During exercise ventilation increases to match higher metabolism.
• Example: breathing into a bag can raise CO2 and help calm hyperventilation.