Introduction to Breathing
- Breathing relies on altering pressure within the thoracic cavity.
- The primary muscle involved is the diaphragm.
- Diaphragm contraction expands the thoracic cavity, creating a pressure difference that draws air in (inspiration).
- Passive recoil of the rib cage returns the cavity to its original size, expelling air (expiration).
- This basic process is known as eupnea and occurs during quiet rest.
Exercise and Breathing
- Physical activity increases CO2 production.
- Elevated CO2 levels are detected by the brain.
- In response, abdominal muscles contract to actively compress the thoracic cavity, forcefully expelling air (expiration).
- This process helps to eliminate excess CO2.
Neural Control of Breathing
- Motor neurons controlling the diaphragm are located in the cervical spinal cord (C3-C5).
- These neurons receive rhythmic signals from a central pattern generator in the medulla.
- The medulla generates the basic breathing rhythm.
- Damage to the cervical spinal cord (above C3) can result in impaired breathing and reliance on assisted ventilation.
- CO2 detection occurs further forward in the brain and triggers signals to abdominal muscles for active expiration.
Conclusion
- Breathing is an essential, largely unconscious process.
- The brain plays a crucial role in regulating breathing through the medulla and spinal cord.
- Spinal cord injuries can significantly impact breathing ability.