Grey matter of the spinal cord

Overview

Location

Central core of the cord, surrounding the central canal throughout its length. It is largest at the cervical and lumbosacral enlargements; lateral horns are present only from T1 to L2.

Parts & subdivisions

1. Posterior (dorsal) horn
   Laminae I–VI. Primary afferents terminate here and synapse on projection neurons (spinothalamic origin in I and V) and on interneurons. Nociceptors end mainly in laminae I–II, and large Aβ touch fibres in III–V.
2. Substantia gelatinosa (lamina II)
   A dense zone of small interneurons that modulates nociceptive input. It is rich in opioid receptors and enkephalinergic interneurons, and is the basis of Melzack–Wall gate control: Aβ input, for example rubbing a bruise, inhibits pain transmission.
3. Lateral horn (intermediolateral column, T1–L2)
   Contains the cell bodies of sympathetic preganglionic neurons. Their axons leave in the ventral roots and white rami communicantes. Damage at T1 can cause Horner syndrome.
4. Sacral parasympathetic nucleus (S2–S4)
   Occupies the equivalent position in sacral segments, but forms no visible horn. It is the origin of the pelvic splanchnic nerves to the bladder, distal colon and erectile tissue.
5. Clarke's nucleus (nucleus dorsalis, C8–L3)
   Lies on the medial base of the dorsal horn in lamina VII. It relays unconscious proprioception from the lower limb and trunk via the dorsal spinocerebellar tract.
6. Anterior (ventral) horn (lamina IX)
   Contains α motor neurons (to extrafusal muscle fibres) and γ motor neurons (to intrafusal spindle fibres). These are the lower motor neurons, the "final common pathway". They are arranged medial for axial muscles, lateral for limb muscles, and ventral for extensors versus dorsal for flexors.
7. Renshaw cells
   Glycinergic interneurons in the ventral horn. They are excited by recurrent collaterals of α motor neurons and inhibit the same and synergistic motor neurons (recurrent inhibition). Tetanus toxin blocks their transmitter release, producing spasms.
8. Grey commissure and lamina X
   Grey matter around the central canal, crossed by commissural fibres. Lamina X receives visceral afferents.

Anatomy

Arterial supply

Mostly the anterior spinal artery, through central (sulcal) branches that supply the anterior and lateral horns and the base of the posterior horn. Posterior spinal arteries supply the tip of the dorsal horn.

Histology

Neuronal cell bodies of very different sizes (α motor neurons up to ≈70 µm), dendrites, unmyelinated and thinly myelinated axons, protoplasmic astrocytes, microglia and capillaries. Nissl staining shows motor neurons with coarse Nissl bodies.

Development

The alar plate of the neural tube forms the dorsal (sensory) horn and the basal plate forms the ventral (motor) and lateral horns. They are separated by the sulcus limitans.

Function

• Receives and processes all somatic and visceral afferent input entering through the dorsal roots.
• Contains the lower motor neurons that drive skeletal muscle (final common pathway).
• Contains interneuronal networks for reflexes, reciprocal inhibition and central pattern generation.
• Gives rise to sympathetic (T1–L2) and sacral parasympathetic (S2–S4) preganglionic outflow.
• Modulates pain transmission (gate control, descending opioid and monoaminergic inhibition).

Clinical significance

Related structures