Figure 2.

Relationship between dorsal root afferents, sympathetic outflow, and the enteric nervous system. Dorsal root afferent neurons (red) pick up information in the gut, skin, muscle, and adipose tissue and conduct it to the dorsal horn (DH) of the spinal cord, where they synapse on spinal large projection neurons and small interneurons (brown) and project via collaterals rostro-caudally over several segments. Projection neurons ascend through anterolateral tracts (ALT) mainly contralaterally to supraspinal targets. Sensory information carried by DRG neurons can also be passed to enteric motor and inter neurons (light brown) in the myenteric plexus, to sympathetic postganglionic neurons in prevertebral ganglia (green) for short-loop reflex actions and possibly also to smooth muscle via axon reflexes. In addition to DRGs, the gut can also communicate to postganglionic sympathetic neurons and spinal cord (not shown) via intrinsic primary afferent neurons (IPANs, blue) and intestinofugal neurons (IF, blue) in the enteric nervous system. These sensory pathways are partly overlapping with the sympathetic nervous outflow system (green). Other abbreviations: bv, blood vessel; DRG, dorsal root ganglion; IML, intermediolateral column; cm, circular muscle; lm, longitudinal muscle mp, myenteric plexus; sma, submucosa; LH and VH, lateral and ventral horn, respectively.