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Robotic Spine Universe

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Grey matter and Rexed laminae

The H-shaped core of the cord. Its horns sort sensory input, drive muscles and run autonomic outflow, and the dorsal horn is layered into laminae that receive different kinds of sensation.

Updated 2026-10-023 sources

Depth:

Why it matters

The grey matter is where the cord does its own processing: reflexes, the first stage of pain processing and the final motor neurons to every muscle below the head all live here [1, 2].

What it is

Grey matter is the tissue with many cell bodies and dendrites; white matter is the tissue with many axons, white because they are insulated by myelin [3]. In cross-section, the cord's grey matter looks like a bulbous capital H and is divided into horns [1]:

  • The posterior horn is responsible for sensory processing [1].
  • The anterior horn sends motor signals to the skeletal muscles; its multipolar motor neurons are among the largest neurons of the cord [1].
  • The lateral horn, found only in the thoracic, upper lumbar and sacral regions, holds autonomic motor neurons [1].

How it works

The dorsal horn is organised into distinct laminae, each associated with particular types of sensory information [2]:

  • High-threshold Aδ and C fibres, which carry pain, heat and itch, end mainly in laminae I and II [2].
  • Aβ and low-threshold Aδ fibres, which carry innocuous touch, project mainly to inner lamina II, III and IV [2].

Within the laminae, incoming fibres synapse on excitatory and inhibitory local interneurons and on projection neurons whose axons run up to the brain [2].

The motor neuron that makes the big toe contract is in the sacral cord; the axons of the anterior horn's motor neurons are the fibres that make skeletal muscle contract [1].

The superficial dorsal horn, laminae I and II, is probably the most studied part of the cord because of its role in processing pain [2]. On this site's cross-sections the laminae are drawn schematically; the atlas used has none of its own.

Common misconceptions

Misconception: The dorsal horn is one uniform relay.

It is layered: different kinds of fibres end in different laminae, and they meet interneurons of both signs as well as projection neurons [2].

Check yourself

Where do pain fibres mainly end in the dorsal horn?

In laminae I and II [2].

At which levels is there a lateral horn?

Thoracic, upper lumbar and sacral [1].

Read next

References

  1. Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, et al.. 13.2 The Central Nervous System. Anatomy and Physiology 2e. OpenStax. 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/13-2-the-central-nervous-system
  2. Rivera-Arconada I, Baccei ML, López-García JA, Bardoni R. An electrophysiologist’s guide to dorsal horn excitability and pain. Frontiers in Cellular Neuroscience. 2025;19. doi:10.3389/fncel.2025.1548252
  3. Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, et al.. 12.1 Basic Structure and Function of the Nervous System. Anatomy and Physiology 2e. OpenStax. 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/12-1-basic-structure-and-function-of-the-nervous-system

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