Pelvic splanchnic nerves

Pelvic splanchnic nerves or nervi erigentes are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the hindgut.

Structure
The pelvic splanchnic nerves arise as branches of spinal nerves S2-S4 (which are part of the sacral plexus). They travel to their side's corresponding inferior hypogastric plexus, located on the side of the rectum.

From there, they contribute to the innervation of the pelvic and genital organs. The nerves regulate the emptying of the urinary bladder and the rectum as well as sexual functions like erection.

They contain both preganglionic parasympathetic fibers as well as visceral afferent fibers.

The parasympathetic nervous system is referred to as the craniosacral outflow; the pelvic splanchnic nerves are the sacral component. They are in the same region as the sacral splanchnic nerves, which arise from the sympathetic trunk and provide sympathetic efferet fibers.

Proximal to the splenic flexure of the transverse colon, the gastrointestinal tract is supplied its parasympathetic fibers by the vagus nerve. Distal to the splenic flexure, the pelvic splanchnic nerves take over.