Overview
This lecture explains how breathing is involuntarily regulated by both the nervous and chemical systems, focusing on the roles of the brain, muscles, and chemoreceptors.
Structure of the Breathing System
- Lungs are located in the rib cage and attached to intercostal muscles.
- The diaphragm is a key muscle beneath the rib cage involved in breathing.
- Intercostal muscles and diaphragm contract and relax to enable inhalation and exhalation.
Neural Regulation of Breathing
- Breathing is both voluntary (can be controlled) and involuntary (happens automatically).
- The medulla oblongata and pons in the brain control involuntary breathing.
- The dorsal respiratory group (DRG) in the medulla sends constant nerve impulses to contract breathing muscles for inhalation.
- The DRG is always active and does not require other brain input for firing impulses.
- The pneumotaxic center in the pons switches off the DRG periodically to allow for exhalation.
- Pneumotaxic center switches off DRG 12–16 times per minute, maintaining a steady breathing rhythm.
Chemical Regulation of Breathing
- Exercise increases carbon dioxide (CO₂) in the blood, making it acidic (lowers pH).
- High CO₂ leads to increased hydrogen ions, increasing blood acidity.
- Chemoreceptors in the carotid artery and aortic arch (peripheral) detect high CO₂ or acidity in the blood.
- Central chemoreceptors near the medulla sense changes in cerebrospinal fluid chemistry.
- Chemoreceptors send signals to the pneumotaxic center to increase breathing rate and depth, supplying more oxygen as needed.
Summary
- Neural control: DRG (medulla) initiates inhalation; pneumotaxic center (pons) triggers exhalation.
- Chemical control: central and peripheral chemoreceptors detect blood/CSF acidity and adjust breathing via the pneumotaxic center.
Key Terms & Definitions
- Intercostal Muscles — muscles between the ribs helping in breathing.
- Diaphragm — large muscle under the lungs aiding in breathing.
- Dorsal Respiratory Group (DRG) — neuron group in medulla controlling inhalation.
- Pneumotaxic Center — neuron group in pons that stops inhalation to allow exhalation.
- Chemoreceptors — sensors detecting CO₂ or pH changes in blood/CSF.
- Central Chemoreceptors — located near medulla, sense CSF acidity.
- Peripheral Chemoreceptors — located in carotid artery and aortic arch, sense blood acidity.
Action Items / Next Steps
- Review the neural and chemical control pathways of breathing.
- Understand the functions of DRG, pneumotaxic center, and chemoreceptors.
- Prepare for questions about involuntary versus voluntary breathing control.