Skip to content
Robotic Spine Universe

Learn · Structure

Spinal nerves and roots

The 31 pairs of mixed nerves that connect the cord to the body. How each forms from a sensory and a motor root, where it leaves the column, and how the nerves regroup into plexuses.

Updated 2026-10-022 sources

Depth:

Why it matters

Every sensation from the body below the head and every command to its muscles crosses a spinal nerve. Spinal nerves extend outward from the vertebral column to innervate the periphery [1].

What it is

There are 31 spinal nerves, named for the level of the cord at which each one emerges: eight cervical, twelve thoracic, five lumbar, five sacral and one coccygeal pair [1]. All of them carry both sensory and motor axons, which separate into two roots near the cord [1]:

  • the dorsal root, through which sensory axons enter the cord [1];
  • the ventral root, through which motor fibres, both somatic and autonomic, emerge [1].

The dorsal root ganglion is an enlargement of the dorsal root that holds the cell bodies of the sensory neurons [1].

How it works

Each nerve leaves the column through the intervertebral foramen at its level [1]:

  • C1 emerges between the occipital bone and the first cervical vertebra, C2 to C7 above the vertebra of the same number, and C8 between C7 and T1 [1];
  • each thoracic and lumbar nerve emerges between the vertebra of the same name and the next one down [1];
  • the sacral nerves emerge from the sacral foramina [1].

The nerves in the periphery are not straight continuations of the spinal nerves: their axons are reorganised, and axons from different spinal nerves come together in systemic nerves [1].

The reorganisation happens in plexuses [1]:

  • The cervical plexus, from C1 to C5, supplies the back of the head and neck and gives the phrenic nerve to the diaphragm [1].
  • Through the brachial plexus, spinal nerves C4 to T1 give rise to the nerves of the arm, including the radial, ulnar and median nerves [1].
  • Thoracic nerves T2 to T11 do not join a plexus; they become the intercostal nerves between the ribs [1].
  • The lumbar plexus gives the femoral nerve, and the sacral plexus, from L4 to S4, gives the sciatic nerve, a combination of the tibial and fibular nerves [1].

When it does not behave

A herniated disc can compress a spinal nerve where it leaves through the intervertebral foramen, causing pain or weakness in the regions that nerve supplies [2]. Sciatica is the result of compression or irritation of the sciatic nerve or of any spinal nerve that forms it [1].

Common misconceptions

Misconception: Each nerve in the arm comes from a single spinal nerve.

The arm's nerves form in the brachial plexus, where axons from spinal nerves C4 to T1 are regrouped [1].

Check yourself

How many pairs of spinal nerves are there?

31: eight cervical, twelve thoracic, five lumbar, five sacral and one coccygeal [1].

Which root carries motor fibres out of the cord?

The ventral root [1].

Read next

References

  1. Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, et al.. 13.4 The Peripheral Nervous System. Anatomy and Physiology 2e. OpenStax. 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/13-4-the-peripheral-nervous-system
  2. Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, et al.. 7.3 The Vertebral Column. Anatomy and Physiology 2e. OpenStax. 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/7-3-the-vertebral-column

For learning only. This page does not diagnose, predict outcomes or recommend treatment. Corrections are welcome: how to suggest one.