General Topography of Autonomic Nervous System

The central autonomic components include regions of the cerebral cortex, diencephalon, and brainstem. In the cerebral cortex, autonomic areas include the frontal premotor areas, telencephalic cortex in the hippocampus, insular cortex, anterior cingulate gyrus, and anteromedial prefrontal cortex. The central nucleus of the amygdala and the bed nucleus of the stria terminalis are known as the extended amygdala and modulate the autonomic responses to emotions.

The hypothalamus integrates autonomic and endocrine responses and includes nuclei in three functional zones: periventricular, lateral, and medial. Nuclei in the periventricular region control biologic rhythms; the suprachiasmatic nucleus, the pacemaker for the circadian rhythms, and the paraventricular nuclei are involved in endocrine responses by modulating the anterior pituitary. The lateral hypothalamic nuclei are involved in arousal and behavior, whereas the medial hypothalamic area, including the medial preoptic region, is involved in homeostatic functions such as thermoregulation. The periaqueductal gray nuclei of the midbrain integrate autonomic and behavioral response to nociceptive environmental stimuli. The parabrachial nucleus of the pons and the nucleus of tractus solitarius in the medulla are the principal relay nuclei in the control of cardiovascular, respiratory, and visceral function in response to environmental stimuli. The reticular formation of the anterolateral medulla contains the primary premotor neurons that control the respiratory motor neurons of the brainstem and cervical spinal cord as well as the sympathetic neurons in the intermediolateral column of the thoracic spinal cord.

These higher and lower levels of representation are interconnected by ascending and descending tracts, or pathways. For example, efferent autonomic inputs originating in the frontal premotor cortical areas descend through fasciculi, usually via synaptic relays in the thalamus, hypothalamus, and reticular formation, and end in certain cranial nerve nuclei and thus influence involuntary muscles, blood vessels, and exocrine and endocrine glands supplied by them. Other fibers descend still farther and form synapses with neurons in the intermediolateral columns in the thoracic and upper two lumbar spinal cord segments, and with neurons in the gray matter of the second to fourth sacral cord segments.

Afferents to the central autonomic area is conveyed by cranial and spinal pathways. Afferent innervation from baroreceptors, chemoreceptors, and pulmonary and gastrointestinal autonomic receptors is conveyed by the vagus and glossopharyngeal nerves to the nucleus of the tractus solitarius. The information is relayed from this nucleus to the more rostral autonomic centers; visceral input and taste are relayed to the anteromedial nucleus of thalamus and then to the insular cortex. Humoral signals are relayed to the central autonomic areas by the circumventricular organs that lack a blood-brain barrier, such as the subfornical organ, the lamina terminalis in the third ventricle, and the area postrema.

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