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Sacral Parasympathetic Nervous System

Pars sacralis systematis nervosi parasympathici

For medical students2 min readUpdated 2026-10-10

The sacral part of the parasympathetic nervous system is a crucial caudal center of autonomic regulation. It provides neural control over the pelvic organs, the distal parts of the alimentary tract, and internal reproductive organs.

Center localizationSpinal cord gray matter (lateral horns), segments S2–S4
Main pathwaysPelvic splanchnic nerves (*nn. splanchnici pelvici*)
Special functionVasodilator fibers for the corpora cavernosa

Central Apparatus of the Sacral Division

The center of the sacral parasympathetic nervous system is strictly localized within the spinal cord. The autonomic neurons that give rise to parasympathetic pathways lie in the gray matter, specifically in its lateral horns.

Topographically, this center spans the sacral spinal cord segments from the second to the fourth (S2–S4). Clusters of these neuronal cell bodies form the sacral parasympathetic nuclei, designated in anatomical nomenclature as nuclei parasympathici sacrales. Impulses directed to the target organs of the caudal half of the body originate precisely from here.

Peripheral Pathways and Fibers

From the nuclei located in the lateral horns of segments S2–S4, preganglionic fibers emerge. They leave the central nervous system and travel to the periphery as part of specific nerve trunks — the pelvic splanchnic nerves (nn. splanchnici pelvici). Historically in literature, these nerves may also be found under the name nn. erigentes.

The further path of the pelvic parasympathetic fibers, running within nn. splanchnici pelvici, proceeds in two main directions:

Target Organs and Parasympathetic Plexuses

Fibers of the sacral parasympathetic center innervate a strictly defined pool of internal organs. Their area of responsibility includes:

  1. Urinary bladder.
  2. Distal segments of the large intestine.
  3. Internal reproductive organs.

It is worth noting separately that vasodilator fibers innervating the blood vessels of the corpora cavernosa belong to this same functional group.

In the pelvic cavity, a complex network of autonomic ganglia and nerve cords is formed. The pelvic parasympathetic plexuses are not formed in isolation: both branches of nn. splanchnici pelvici and sympathetic fibers participate in their formation. As a result, a mixed autonomic network is created.

The base and largest collector is the inferior hypogastric plexus (plexus hypogastricus inferior). Organ-specific plexuses form from it and its associated structures:

Mnemonic

To remember the sacral center segments (S2–S4) and their function, use the rule: "S2, S3, S4 — keeps the pelvic floor off the floor" (S2–S4 innervate the pelvic organs).

Frequently asked questions

In which part of the spinal cord is the center of the sacral parasympathetic division located?

The center is located in the gray matter of the spinal cord, specifically in its lateral horns at the level of segments S2–S4.

What are the nerves called through which preganglionic fibers travel?

Preganglionic fibers exit within the pelvic splanchnic nerves, which are called nn. splanchnici pelvici in Latin (or nn. erigentes).

With which fibers do *nn. splanchnici pelvici* merge when forming the pelvic plexuses?

Pelvic parasympathetic fibers form the pelvic plexuses with the participation of sympathetic fibers.

To which ganglia do the parasympathetic fibers in the organ walls head?

The fibers head toward the intramural ganglia of the pelvic organs, as well as to the inferior hypogastric plexus.

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