Fig. 1

Involuntary control of breathing: Structures: 1. Anterior portion of the insular cortex; 2. Hypothalamus; 3. Stem centers: pneumotaxic center of the pons and ventral and dorsal respiratory groups of the pontobulbars (nucleus ambiguus and solitary nucleus, respectively), locus coeruleus; 4. Intermediolateral column of the spinal cord; 5. Superior cervical ganglion; 6. Bronchioalveolar receptors and accessory muscles of respiration. Control mechanism: The peripheral chemoreceptors of the carotid bulbs and aortic arch innervated by the glossopharyngeal nerve (activated by hypoxia, increased CO₂, decreased arterial pH or hypoperfusion), project to the nucleus of the solitary tract, and this, together with the locus coeruleus, are central sensors of CO₂ concentrations. These afferent nuclei plus the efferent nuclei in the ventral and dorsal pontobulbar groups have descending pathways to the intermediolateral column of the spinal cord, which contains sympathetic preganglionic neurons, in turn making efference through the superior cervical ganglion to the bronchi, alveoli, and accessory muscles of respiration. The structures of the indicated stem and the lateral intermediate column of the spinal cord receive superior control from the insula and hypothalamus, with sympathetic and parasympathetic autonomic control, which, when altered by central lesions, lead to the alteration of the predominantly sympathetic respiratory cycle. Created by authors