Neural Control of Respiration

The medullary respiratory center in the medulla oblongata and the pontine respiratory group in the pons are the two primary respiratory centers. The medullary center contains the dorsal respiratory group (DRG) and ventral respiratory group (VRG), which work together to regulate breathing. The pontine respiratory group fine-tunes breathing rhythms during vocalization, sleep, and exercise by transmitting impulses to the medullary center.

The dorsal respiratory group sends impulses via the phrenic and intercostal nerves to the diaphragm and external intercostal muscles, causing them to contract and induce inhalation. These impulses are released in bursts, starting weakly and escalating in strength for about two seconds. After this period, DRG activity ceases, allowing the muscles to relax and exhalation to occur passively.

The pre-Bötzinger complex, a cluster of neurons within the ventral respiratory group, generates the breathing rhythm by regulating the rate at which dorsal respiratory group neurons fire action potentials. This specialized neural network is integral to establishing and maintaining the basic rhythm of breathing during normal, quiet respiration.

The ventral respiratory group becomes particularly active during forceful breathing, such as during exercise or playing wind instruments. Its neurons control both forceful inhalation and exhalation by regulating the accessory breathing muscles. This allows the body to increase ventilation intensity beyond normal quiet breathing patterns.

The pontine respiratory group transmits impulses to the ventral respiratory group of the medulla, modifying and fine-tuning the breathing rhythms produced by the medullary center. This interaction allows the pontine group to adjust breathing patterns during specific activities like vocalization, sleep, and exercise, demonstrating hierarchical neural control of respiration.

The dorsal respiratory group becomes inactive after approximately two seconds of firing, allowing the diaphragm and external intercostal muscles to relax. This inactivity permits passive recoil of the lungs and thoracic wall, resulting in exhalation. The ventral respiratory group's pre-Bötzinger complex regulates this timing to establish the rhythmic breathing cycle.

The respiratory centers adjust breathing through hierarchical control: the medullary center generates basic rhythm, the pontine respiratory group fine-tunes patterns during vocalization and sleep, and the ventral respiratory group activates accessory muscles during exercise. This coordinated response to chemical factors affecting respiration centers allows the body to meet varying oxygen and carbon dioxide demands across different activities.