Regulation of Breathing

Medullary rhythmicity center, pneumotaxic and apneustic centers of the pons, central and peripheral chemoreceptors, and proprioceptor stimulation.

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Regulation of Breathing

Respiratory Center Overview

The respiratory center is located in the medulla oblongata and pons of the brainstem. It is organized into three major neuron groups that coordinate the rhythm and depth of breathing.

Medullary Rhythmicity Center

Located in the medulla oblongata, this center controls the basic rhythm of breathing.

Inspiratory Area: Sends nerve impulses for approximately 2 seconds to the muscles of inhalation — the diaphragm (via the phrenic nerve, C3–C5) and the external intercostals. At the end of 2 seconds, impulses stop and passive exhalation occurs.

Expiratory Area: Remains inactive during quiet breathing. During forceful breathing, the inspiratory area activates the expiratory area, which stimulates the internal intercostals and abdominal muscles to contract, producing forceful exhalation.

Pneumotaxic Center (Upper Pons)

Helps coordinate the transition from inhalation to exhalation. It sends inhibitory signals to turn off the inspiratory area before the lungs become overfilled. This shortens inhalation duration. Greater pneumotaxic activity results in more rapid breathing.

Apneustic Center (Lower Pons)

Sends stimulatory impulses to the inspiratory area, prolonging inhalation and producing long, deep breaths. The pneumotaxic area can override apneustic signals to prevent overinflation.

Cortical Influence

The cerebral cortex can voluntarily alter the breathing pattern, allowing breath holding, speaking, and singing. However, breath holding is limited by rising CO₂ and H⁺ levels, which eventually override voluntary control — or fainting causes breathing to resume automatically.

Chemoreceptor Regulation

The respiratory system maintains CO₂ and O₂ levels via chemoreceptors. The hydrolysis equation underlies CO₂ transport: CO₂ + H₂O ↔ H₂CO₃ ↔ HCO₃⁻ + H⁺.

Central Chemoreceptors: Located in or near the medulla, they respond to H⁺ concentration or PCO₂ in the cerebrospinal fluid (CSF).

Peripheral Chemoreceptors: Located in the aortic arch and carotid bodies (oval nodules in the common carotid arteries). They respond to changes in PO₂, PCO₂, and [H⁺] in the blood. Oxygen deficiency triggers increased rate and depth of breathing.

Proprioceptor Stimulation

At the onset of exercise, proprioceptors in muscles, tendons, joints, and the inner ear stimulate the inspiratory area, increasing the rate and depth of breathing. This response occurs before any chemoreceptor changes take place.