Respiratory Rhythm Centre

The respiratory center is located in the brainstem’s medulla oblongata and pons. The respiratory center is composed of three major respiratory groups of neurons, two of which are located in the medulla and one of which is located in the pons. The dorsal respiratory group is located in the medulla, while the ventral respiratory group is located in the cortex. The pontine respiratory group is divided into two areas in the pons: the pneumotaxic center and the apneustic center

The respiratory centre is in charge of generating and maintaining the respiratory rhythm, as well as adjusting it in homeostatic response to physiological changes. To regulate the rate and depth of breathing, the respiratory centre receives input from chemoreceptors, mechanoreceptors, the cerebral cortex, and the hypothalamus. The input is stimulated by changes in oxygen, carbon dioxide, and blood pH, by hypothalamic hormonal changes associated with stress and anxiety, and by signals from the cerebral cortex that provide conscious control of respiration. Injury to the respiratory groups can result in a variety of breathing disorders, some of which require mechanical ventilation, and is frequently associated with a poor prognosis.

Respiratory groups in the respiratory center and their influence

Respiratory groups

In the medulla and pons, the respiratory center is divided into three major groups. The dorsal and ventral respiratory groups are found  in the medulla. The pneumotaxic and apneustic centers of the pontine respiratory group are located in the pons. The basic rhythm of respiration is controlled by the ventral  and dorsal  ventral medullary groups. On either side of the brain stem, two groups are paired.

Dorsal respiratory group

The DRG plays a crucial role in kicking off inspiration (inhalation). There are many neurons in the DRG which form an elongated mass that covers a large portion of the dorsal medulla. Both of these groups are located close to the spinal cord’s central canal. They control and regulate the rate at which a person breathes. The solitary tract’s nucleus contains most of the neurons. The reticular substance of the medulla contains other important neurons. The pontine respiratory group and two cranial nerves – the vagus nerve and the glossopharyngeal nerve – send sensory information to the solitary nucleus. The solitary nucleus receives signals from peripheral chemoreceptors, baroreceptors, and other pulmonary receptors, particularly stretch receptors. To modify breathing rhythm, the dorsal respiratory group acts as an integrating center.

The dorsal respiratory group’s solitary tract nucleus and the ventral respiratory group’s ambiguous nucleus are shown in their positions on the medulla oblongata.

Ventral respiratory group

The ventral respiratory group (VRG) is made up of four groups of neurons that control exhalation (expiration). This area is 5 mm anterior and lateral to the dorsal respiratory group in the medulla. The nucleus ambiguus, retroambiguus, and pre-Bötzinger complex interneurons are involved. Virtually all VRG neurons are inspiratory. This group of neurons is active during forceful breathing and inactive during quiet, restful breathing. VRG inhibits apneustic centers.

Pontine respiratory group

The pontine respiratory group (PRG) comprises the pneumotaxic and apneustic centers located in the pontine tegmentum of the pons. These are connected to one another and to the solitary nucleus.

i. Pneumotaxic center

Pneumotaxic centers are located in the pons’s upper portion. The sub parabrachial nucleus and the medial Para brachial nucleus are its nuclei. [8] Both the rate and pattern of breathing are regulated by the pneumotaxic center. The pneumotaxic center is thought to act as an antagonist to the apneustic center (which results in abnormal breathing during inhalation), inhibiting inhalation cyclically. The pneumotaxic center is in charge of limiting inspiration and acting as an inspiratory shut-off switch (IOS). It effectively decreases the tidal volume and regulates the respiratory rate by limiting the burst of action potentials in the phrenic nerve. Without the center, the depth of respiration increases and the respiratory rate decreases.

ii. Apneustic center

The apneustic center in the lower pons appears to promote inhalation by continuously stimulating neurons in the medulla oblongata. The apneustic center communicates with the dorsal group in the medulla to delay the switch off,’ the inspiratory off switch (IOS) signal from the pneumotaxic Centre’s inspiratory ramp. It regulates the rate of breathing by sending positive impulses to the neurons responsible for inhalation. The pulmonary stretch receptors, as well as the pneumotaxic center, inhibit the apneustic center. Additionally, it sends an inhibiting impulse to the pneumotaxic center.

Respiratory rhythm

Breathing is the repetitive process of inhaling air and exhaling waste products from the lungs. The oxygen derived from the air is a constant, ongoing requirement for an organism to survive. This requirement persists during sleep, which means that this process must be automatic and integrated into the autonomic nervous system. The inhalation is followed by the exhalation, completing the respiratory cycle. The respiratory cycle is divided into three phases: inspiration, subsequent inspiration or passive expiration, and late or active expiration. 

The respiratory rate is expressed in cycles per minute. The dorsal respiratory group in the medulla controls the respiratory rate, and these neurons are primarily concentrated in the solitary nucleus that extends the length of the medulla. 

The fundamental rhythm of respiration is eupnea, or quiet, restful breathing. Quiet breathing requires only the dorsal group of muscles, which activates the diaphragm, and the external intercostal muscles to contract. Exhalation is a passive process that relies on the lungs’ elastic recoil. When the metabolic demand for oxygen increases, inspiration becomes more vigorous and the ventral group of neurons is activated, resulting in vigorous exhalation. Dyspnea is the polar opposite of eupnea.

Conclusion 

These are in the medulla oblongata and the pons. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. The ventral respiratory group is located in the cortex. The pontine respiratory group is divided into two parts: pneumotaxic and apneustic. The respiratory center generates, maintains, and adjusts the respiratory rhythm in homeostatic response to physiological changes. This center receives input from chemoreceptors, mechanoreceptors, the cortex, and the hypothalamus. Changes in oxygen, carbon dioxide, and blood pH, as well as signals from the cerebral cortex that provide conscious control of respiration, all stimulate the input. Respiratory group injury can cause a variety of breathing disorders, some requiring mechanical ventilation, and has a poor prognosis. This center is divided into three parts in the medulla and pons. The medulla has dorsal and ventral respiratory groups. The pons houses the pontine respiratory group’s pneumotaxic and apneustic centers. The dorsal and ventral medullary groups control the basic respiration rhythm. Each side of the brain stem has two groups.