Ventral respiratory group

The respiratory center is located in the medulla oblongata and pons, in the brainstem. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal respiratory group, and the ventral respiratory group. In the pons, the pontine respiratory group includes two areas known as the pneumotaxic centre and the apneustic centre. The respiratory centre is responsible for generating and maintaining the rhythm of respiration, and also of adjusting this in homeostatic response to physiological changes. The respiratory center receives input from chemoreceptors, mechanoreceptors, the cerebral cortex, and the hypothalamus in order to regulate the rate and depth of breathing. Input is stimulated by altered levels of oxygen, carbon dioxide, and blood pH, by hormonal changes relating to stress, and anxiety from the hypothalamus, and also by signals from the cerebral cortex to give a conscious control of respiration. Injury to respiratory groups can cause various breathing disorders that may require mechanical ventilation, and is usually associated with a poor prognosis. The respiratory centre is divided into three major groups, two in the medulla and one in the pons. The two groups in the medulla are the dorsal respiratory group and the ventral respiratory group. In the pons, the pontine respiratory group is made up of two areas – the pneumotaxic centre and the apneustic centre. The dorsal and ventral medullary groups control the basic rhythm of respiration. The groups are paired with one on each side of the brainstem. The dorsal respiratory group (DRG) has the most fundamental role in the control of respiration, initiating inspiration (inhalation). The DRG is a collection of neurons forming an elongated mass that extends most of the length of the dorsal medulla. They are near to the central canal of the spinal cord, and just behind the ventral group. They set and maintain the rate of respiration. Most of the neurons are located in the nucleus of the solitary tract. Other important neurons are found in the adjacent areas including the reticular substance of the medulla. The solitary nucleus is the end-point for sensory information arriving from the pontine respiratory group, and from two cranial nerves – the vagus nerve, and the glossopharyngeal nerve. The solitary nucleus sends signals to the respiratory center from peripheral chemoreceptors, baroreceptors, and other types of receptors in the lungs in particular the stretch receptors. The dorsal respiratory group is thus seen as an integrating center that gives output to the ventral respiratory group to modify the breathing rhythm. In the medulla, the ventral respiratory group (VRG) consists of four groups of neurons that make up the exhalation (expiratory) area of respiratory control. This area is in the ventrolateral part of medulla, about 5 mm anterior and lateral to the dorsal respiratory group. The neurons involved include those in the nucleus ambiguus, the nucleus retroambiguus, and the interneurons in the pre-Bötzinger complex. The VRG contains both inspiratory and expiratory neurons. In quiet, restful breathing, the ventral respiratory group of neurons are inactive. They become active in forceful breathing. The VRG sends inhibitory impulses to the apneustic center.