FIGURE 16-16 Stress-Activating System (A) Medial view showing that in the brainstem, cell bodies of noradrenergic (norepinephrine) neurons emanate from the locus coeruleus (top) and cell bodies of the serotonergic activating system emanate from the raphe nuclei (bottom). (B) When activated, the HPA axis affects mood, thinking, and indirectly, cortisol secretion by the adrenal glands. HPA deactivation begins when cortisol binds to hypothalamic receptors.