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Lumbar, Sacral and Coccygeal Nerves

Nervi lumbales, sacrales et coccygeus

For medical students2 min readUpdated 2026-10-10

The lumbar, sacral, and coccygeal nerves connect the nervous system to the lower half of the body. Like other spinal nerves, they feature a precise branching architecture where the anterior rami form the robust lumbosacral plexus, while the posterior rami supply the muscles and skin of the back.

Four BranchesEach nerve divides into meningeal, communicating, posterior (dorsal), and anterior (ventral) rami.
PlexusesThe anterior rami combine to form the common lumbosacral plexus.
Gluteal SkinInnervated by lateral branches originating from segments L₁–L₃.

General Branching Pattern of Spinal Nerves

The lumbar, sacral, and coccygeal nerves follow the general principles of spinal nerve anatomy. Upon exiting the intervertebral foramen, each trunk divides into four obligatory groups of branches:

  1. Meningeal branches (rr. meningei) — re-enter the vertebral canal.
  2. Communicating branches (rr. communicantes) — connect the somatic nervous system with the autonomic nervous system.
  3. Posterior rami (rr. dorsales) — travel posteriorly to the back of the trunk.
  4. Anterior rami (rr. ventrales) — travel anteriorly and are the largest, as they form the nerve plexuses.

The collection of all anterior rami from these segments forms a single, massive lumbosacral plexus (plexus lumbosacralis).

Anatomy of the Lumbar Nerves (L₁–L₅)

The lumbar spinal nerves (nn. lumbales) comprise five pairs. Their branches are highly specialized.

Posterior rami of the lumbar nerves (rr. dorsales nn. lumbalium) classically subdivide into two bundles:

Of particular interest are the lateral cutaneous branches arising from the upper three lumbar nerves (L₁–L₃). They pierce the muscle mass, penetrate the thoracolumbar fascia, and descend inferior to the iliac crest. Their ultimate target is the innervation of the skin of the gluteal region. In clinical anatomy, these structures are termed the superior cluneal nerves (nn. clunium superiores).

Important nuance: The posterior rami of the lower two lumbar segments (L₄ and L₅) have no cutaneous representation. They supply branches exclusively to the muscular structures of the back and lower back.

Formation of the Lumbar Plexus

While the posterior rami head toward the back, the anterior rami of the lumbar nerves (rr. ventrales nn. lumbalium) form plexuses.

The anterior rami of the first four lumbar nerves (L₁–L₄), joined by a minor contribution from the twelfth thoracic nerve (Th₁₂), unite to form the lumbar plexus (plexus lumbalis), which constitutes the upper tier of the overall lumbosacral plexus.

Mnemonic

To remember the origin of the superior cluneal nerves, use the rule "Upper buttocks equal the first three lumbars": the nn. clunium superiores arise strictly from the posterior rami of L1, L2, and L3.

Frequently asked questions

Which branches of the spinal nerves form the lumbosacral plexus?

The plexus is formed exclusively by the anterior rami (rr. ventrales) of the corresponding spinal nerves.

Do the L4 and L5 nerves participate in the sensory innervation of the back skin?

No, the posterior rami of the fourth and fifth lumbar nerves (L4–L5) do not innervate the skin; they provide motor fibers exclusively to muscles.

Which segments form the lumbar plexus (plexus lumbalis)?

The lumbar plexus is formed by the anterior rami of the first through fourth lumbar nerves (L1–L4), with a mandatory contribution from the twelfth thoracic nerve (Th12).

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