Central Respiratory Neuron

The precise organization of the central respiratory neurons is still a matter of contention. Although there may be respiratory pacemaker cells in which spontaneous changes in transmembrane potential occur, in the intact system, the respiratory rhythm depends on interconnections between different respiratory neurons.
Because breathing is preserved in anesthetized animals even after removal of the brain rostral to the pons, it is believed that the neurons on which respiratory rhythm critically depends are located in the bulbopontine region. Many investigators believe that the essential features of the respiratory rhythm remain even after separation of the pons from the medulla, and that the central pattern generator must be anatomically located within the confines of the medulla. There is evidence, however, that pontine neurons, particularly the complex composed of the nucleus parabrachialis medialis (NPBM) and the Kölliker-Fuse nucleus (KFN), as well as nuclei in the tegmentum (magnocellular and gigantocellular nuclei), significantly modify breathing.
In addition to these pontine and medullary respiratory neuronal aggregates, neurons with activity that is modulated by respiration can be found all through the brain stem intermixed with nonrespiratory neurons. It also has been shown that when breathing is stimulated, respiratory modulation of the activity of these neurons decreases according to level of anesthesia and sleep state.
A number of neurons whose firing patterns demonstrate a respiratory modulation but whose phase relationships with phrenic motor activity and with one another differ have been identified in the brain stem. Some of these neurons project to the spinal cord (bulbospinal) and are therefore true premotor cells. The remainder have axons that project to other parts of the brain (propriobulbar). Only the function of the bulbospinal neurons has been determined with any degree of certainty. It is generally believed, however, that the propriobulbar cells actively inhibit or excite other neurons involved in the respiratory cycle. The precise function of these propriobulbar neurons remains under investigation, although it is generally agreed that they are organized into networks whose complicated interactions determine the level of excitation of the bulbospinal neurons and produce respiratory phase switching.