Figure 1.

Anatomical organization of the autonomous nervous system. The autonomous nervous system is organized in three anatomical and biochemical distinct systems. (1) The sympathetic nervous system has its preganglionic cell bodies in the thoraco-lumbar region (sympathetic trunk). The pregangliotic sympathetic neurons synapses with the postgangionic neuron in the sympathetic trunk, whereas the long postganglionic neuron (red) innervates the respective part of the gastro-intestinal tract. (2) The cell bodies of the parasympathetic nervous system are located in the brainstem and the pelvic sacral nerves. The vagal nerve includes preganglionic fibers from parasympathetic nervous system (green) that innervates the gastro-intestinal tract and ends just before the splenic flexure of the transverse colon (also known as Cannon's point). After Cannon's point, the colon is innervated by the pelvic sacral plexus. The postganglionic neuron is localized in immediate proximity to the target organ. (3) The enteric nervous system is located within intestinal tissues (Auerbach plexus, Meissner plexus) and has a characteristic architecture (details see Figure 2).