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Understanding the Control of Breathing
Dec 9, 2024
Lecture on Control of Breathing
Introduction
Follow-up to lectures on ventilation and exercise.
Previous topics covered:
Ventilation increases with exercise intensity and CO2 production.
Reasons for ventilation increase: metabolic, mechanical.
Ventilation kinetics: Phase 1 (cardio-dynamic), Phase 2, Phase 3.
Focus of this lecture: control of breathing.
Voluntary Control of Ventilation
Unique to respiratory system compared to cardiovascular system.
Can control:
Breath-holding.
Ventilation amplitude and frequency.
Ventilation Mechanics at Rest vs. Exercise
At rest
:
Active inspiration (diaphragm contraction).
Passive expiration (elastic recoil).
During exercise
:
Both inspiration and expiration are active.
Accessory muscles (intercostal, sternocleidomastoid, abs) involved.
Expiratory centers controlled by inspiratory centers.
Respiratory Centers
Located in the brainstem: medulla and pons.
Medulla's role:
Evaluating and prioritizing neural signals.
Interaction between voluntary and physiological needs (e.g., holding breath vs. need to breathe due to CO2 levels).
Pons' role:
Fine-tuning and modifying breathing patterns during activities.
Chemoreceptors
Central Chemoreceptors
:
Located in the brain.
Sensitive to CO2 and H+ ions (pH changes).
Major feedback for ventilation control (~70%).
Peripheral Chemoreceptors
:
Located in carotid bodies and aortic bodies.
Sensitive mainly to oxygen levels.
Can modulate response based on CO2 and H+.
Contribute ~20% to ventilation control.
Other Receptors Influencing Ventilation
Mechanoreceptors
: in muscles, sensitive to tension/stretch.
Temperature receptors
: in hypothalamus.
Pulmonary receptors
: include stretch receptors, involved in reflexes like the Hering-Breuer reflex.
Summary of Breathing Control
Integration of signals from central and peripheral chemoreceptors and other receptors.
Pons and Medulla
:
Work together to regulate breathing via inspiratory and expiratory centers.
Pons influences medulla for fine-tuning ventilation based on metabolic demands.
Feedback loops from all parts of the body to respiratory centers.
Conclusion
Overview of control of ventilation and its complexity.
Upcoming lectures will focus on specific chemoreceptors (central and peripheral) and their roles during exercise.
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