Dorsal Horn of the Spinal Cord: Gateway for Sensory Input

The dorsal (posterior) horn of the spinal cord gray matter receives primary afferent sensory fibers via the dorsal roots. It is the first central relay for somatic sensation.

Organization (Rexed Laminae I–VI)

• Lamina I (marginal zone): Nociception, temperature (Aδ, C fibers); projects to thalamus (spinothalamic).
• Lamina II (substantia gelatinosa): Modulates nociception; interneurons (GABA, glycine, opioids); gate control.
• Lamina III–IV: Light touch, pressure (Aβ fibers).
• Lamina V–VI: Wide dynamic range (WDR) neurons (convergent nociceptive + non-nociceptive); deep pressure, visceral input; project to thalamus and cerebellum.

Afferent Pathway

1. Peripheral receptor → dorsal root ganglion (pseudounipolar neuron cell body).
2. Central process → dorsal root → dorsal horn (synapse or ascend in dorsal column).
3. Second-order neurons cross (spinothalamic) or ascend ipsilaterally (dorsal column-medial lemniscus).

Clinical Relevance

• Dorsal column lesion → loss of vibration, proprioception, fine touch (ipsilateral).
• Spinothalamic lesion → loss of pain/temperature (contralateral, 1–2 levels below).
• Syringomyelia: central cavity → crossing spinothalamic fibers → cape distribution sensory loss.
• Gate control theory: Aβ input inhibits lamina II → TENS, rubbing reduce pain.