Figure 14 Three sets of peripheral nerves are involved in penile erection: two are autonomic and one is somatic. Parasympathetic nerves stem from the second to the fourth sacral segments (S2–S4), whereas sympathetic nerves have their preganglionic cell bodies in the intermediolateral cell columns of the thoracolumbar (T10–L2) segments. Somatic fibers travel in the pudendal nerves and their cell bodies are situated in the S2–S4 segments