Figure 1.

The central sympathetic nervous system [SNS] is located in the medulla and modulated by the hypothalamus. The motor outflow of the SNS is formed by two sets of neurons connected in tandem, the pre-ganglionic neurons originating in the brain stem or the spinal cord, and the post-ganglionic neurons located in the sympathetic ganglia. The main neurotransmitter of the SNS pre-ganglionic neurons is acetylcholine, while the main neurotransmitter of most SNS post-ganglionic neurons is norepinephrine. SNS activity is decreased (–) by the arterial baroreceptor reflex and the cardiopulmonary reflex and augmented (+) by the cardiac SNS afferent reflex (CSAR) and the arterial chemoreceptor reflex. H = hypothalamus; M = medulla. With permission from ref. [1].