Figure 25-6. Comparisons of three main types of neurally mediated syncope. Syncope is associated with profound decline in blood pressure and in diastolic cerebral blood flow velocity (CBFv). The heart rate and blood pressure responses differentiate each type of syncope while CBFv responses are similar among all syncope types. Heart rate declines before blood pressure in cardiovagal syncope, the heart rate decline is absent in the vasodepressor syncope and heart rate and blood pressure decline simultaneously in mixed syncope. CBFv shows typical vasodilation pattern in all types of syncope that is characterized by decline in diastolic and increase in systolic CBFv. The diastolic CBFv is equal or close to zero during syncope. (Modified and with permission from Novak P: Cerebral blood flow, heart rate, and blood pressure patterns during the tilt test in common orthostatic syndromes. Neurosci J 2016:6127340, 2016 (epub).) + or –+ or –+ or –VisualAuditoryTactileOlfactoryGustatoryMemoryImaginative“PSYCHICSTIMULATION”LimbiclobeThoraco-lumbarerectioncenterSacralerectioncenterS2, 3, 4VasodilationIncreased blood flowthrough penisERECTIONNervierigentesPudendalnerve“REFLEXOGENICSTIMULATION”Exteroceptivee.g., tactile stim.of genitaliaInteroceptivebowelbladder
Figure 25-7. The pathways involved in human penile erection. See text for details. (Reproduced by permission from Weiss.)
PRGVIIN. ambiguusN. ambiguusPre-BotzingerRostralRostral VRGCaudalVRGIX, XN. tractussolitariusDRGDRGXII
Figure 25-8. The location of the main centers of respiratory control in the brainstem as currently envisioned from animal experiments and limited human pathology. There are three paired groups of nuclei: (1) The dorsal respiratory group (DRG), containing mainly inspiratory neurons, located in a subnucleus of the nucleus of the tractus solitarius; (2) a ventral respiratory group (VRG), situated near the nucleus ambiguus and containing in its caudal part neurons that fire predominantly during expiration and in its rostral part neurons that are synchronous with inspiration—the latter structure merges rostrally with the Botzinger complex, which is located just behind the facial nucleus and contains neurons that are active mostly during expiration; and (3) a pontine pair of nuclei (PRG), one of which fires in the transition between inspiration and expiration and the other between expiration and inspiration. The intrinsic rhythmicity of the entire system probably depends on interactions between all these regions, but the “pre-Botzinger” area in the rostral ventromedial medulla may play a special role in generating the respiratory rhythm. (Adapted by permission from Duffin et al.)
Chapter  25    Disorders of the Autonomic Nervous System, Respiration, and Swallowing
The Hypothalamus and
The hypothalamus plays three roles in the actions of the nervous system. First, it serves as the “head ganglion” of the autonomic nervous system, as described in the preceding chapter; second, it is a circadian and seasonal clock for behavioral and sleep–wake functions, as considered in Chap. 18 on sleep; third, it provides neural control of the endocrine system, as discussed in this chapter. The hypothalamus integrates these systems with one another as well as with neocortical, limbic, and spinal networks. Ultimately, the hypothalamus maintains complex homeostatic functions and participates in the substructure of emotion and affective behavior.