Figure 1. Hierarchical organization of reflex control of autonomic outflow. A schematic diagram of the possible interconnections between the regions of the CNS known to be involved in the central nervous integration of cardiovascular control. Reproduced with permission from Jordan and Marshall (1995). Copyright Portland Press.

Figure 2. Medullary pathways underlying the baroreceptor reflex. Baroreceptor afferent fibres travelling in the carotid sinus and aortic nerves terminate in the NTS where information is processed. Interneurons project to the nucleus ambiguus to activate parasympathetic fibres that travel in the vagus to slow the heart and the ventrolateral medulla, where they activate ascending GABA-containing interneurons. These project to the RVLM to inhibit the spinally projecting neurons that excite sympathetic preganglionic neurons in the spinal cord. For clarity, the parasympathetic and sympathetic pathways are shown on opposite sides of the brain.

Figure 3. Schematic diagram indicating the respiratory and cardiovascular components of the alerting response and the changes in nerve activity that produce them. In the upper part of the figure, pink lines indicate influences on sympathetic outflow, green lines indicate influences on parasympathetic outflow, and orange lines show influences on somatic motor outflow; + and – indicate an increase and decrease in activity, respectively. HR, heart rate. Reproduced with permission from Jordan and Marshall (1995). Copyright Portland Press.

Figure 4. Schematic diagram illustrating the possible pathways responsible for auditory conditioning of fear responses. Auditory input reaches the thalamus (medial geniculate nucleus) and can evoke a fear response by a short pathway to the amygdala. However, to discriminate fully between similar auditory stimuli, cortical regions are involved, and to invoke spatial and contextual components of emotional responses requires the involvement of hippocampal pathways. Based on data taken from Le Doux, (2001).