Overview
This lecture explains how the brain's respiratory center coordinates breathing by integrating chemical, mechanical, emotional, and voluntary signals, and controls key muscle groups involved in respiration.
Respiratory Center in the Brain
- Two main brain areas (respiratory centers) control how fast and deep we breathe.
- These centers coordinate by sharing information among neurons to regulate breathing appropriately for every situation.
- The respiratory center gathers input, decides, and then controls breathing actions.
Chemical Input: Chemoreceptors
- Central chemoreceptors, located in the brain, detect carbon dioxide (CO₂) and pH levels but not oxygen levels.
- Peripheral chemoreceptors (aortic body and carotid body) detect oxygen, CO₂, and pH and send signals to the brain.
- Carotid body signals travel via the glossopharyngeal nerve (cranial nerve IX).
- Aortic body signals travel via the vagus nerve (cranial nerve X).
Mechanical Input: Mechanoreceptors
- Mechanoreceptors detect pressure or stretch in the nose, lungs, and GI tract.
- Baroreceptors are a type of mechanoreceptor in blood vessels sensing blood pressure.
- Nose mechanoreceptors send signals through the trigeminal nerve (cranial nerve V).
- Lung and GI tract mechanoreceptors use the vagus nerve (cranial nerve X).
- Examples: Inhaled pollen triggers nose mechanoreceptors, while lung stretch receptors signal fullness to prompt exhalation.
Emotional and Voluntary Inputs
- Hypothalamus sends emotional state signals (anxiety, fear, pain) to the respiratory center, affecting breathing pattern.
- The cerebrum enables voluntary control of breathing, allowing actions like singing or yelling.
Output: Motor Control of Breathing Muscles
- The respiratory center sends motor signals to four main muscle groups:
- Diaphragm (C3–C5 spinal nerves)
- Intercostal muscles (T1–T11 spinal nerves)
- Abdominal muscles (T6–L1 spinal nerves)
- Accessory muscles in the neck (C1–C3 spinal nerves)
- These muscles collectively enable effective inhalation and exhalation.
Key Terms & Definitions
- Respiratory Center — brain region coordinating breathing rate and depth.
- Chemoreceptor — sensor detecting chemical changes, such as CO₂, oxygen, or pH.
- Central Chemoreceptor — chemoreceptor in the brain monitoring CO₂ and pH.
- Peripheral Chemoreceptor — chemoreceptors outside the brain monitoring oxygen, CO₂, and pH.
- Mechanoreceptor — sensor detecting mechanical changes like stretch or pressure.
- Baroreceptor — mechanoreceptor in blood vessels sensing blood pressure.
- Accessory Muscles — neck muscles aiding breathing during increased demand.
Action Items / Next Steps
- Review the roles of different nerves (V, IX, X) in transmitting sensory input to the respiratory center.
- Memorize spinal nerve origins for each respiratory muscle group.