Anatomical Location and Formation
The spinal ganglion is located on the dorsal root (radix posterior / dorsalis) of the spinal cord, which consists predominantly of afferent (sensory) nerve fibers.
The dorsal root joins the ventral (motor) root lateral to the spinal ganglion. This junction forms the mixed trunk of the spinal nerve (truncus nervi spinalis), containing both sensory and motor fibers.
Histological Structure
Microscopic examination using hematoxylin and eosin (H&E) staining reveals pseudounipolar neurons within the spinal ganglion.
Each such neuron features:
- Peripheral process — extends toward sensory receptors.
- Central process — enters the spinal cord as part of the dorsal root.
Involved Pathways
Cells of the spinal ganglion act as the first-order neuron (I) for ascending sensory tracts and reflex arcs:
- Anterior spinothalamic tract (tractus spinothalamicus anterior) — conducts crude touch and pressure sensation. Signals originate from peritrichial nerve endings and tactile corpuscles.
- Lateral spinothalamic tract (tractus spinothalamicus lateralis) — conducts pain and temperature sensation.
- Spinocerebellar tracts — the anterior tract of Gowers and the posterior direct tract; they convey unconscious proprioception from muscle and tendon receptors to the cerebellum.
- Simple somatic reflex arc — the ganglion serves as the afferent limb of tendon reflexes, including the knee-jerk reflex. Signals from muscle spindles travel via the ganglion to motor neurons in the anterior horns.
Fiber Distribution Upon Entering the Spinal Cord
The central processes of ganglion cells divide into two groups upon entering the spinal cord:
- Medial group — thick, heavily myelinated fibers. They enter the dorsal funiculus and bifurcate in a T-shape. Ascending branches form the gracile and cuneate fasciculi, ascending to the medulla oblongata. Descending branches synapse with cells in the posterior columns of lower segments. In the thoracic and cervical regions, this bundle appears comma-shaped; in the lumbar region, it forms an oval field.
- Lateral group — thin, lightly myelinated fibers. They project toward the posteromarginal nucleus and then enter the posterior column to synapse with its cells.
Clinical Significance and Topography
- Lesion Syndrome: Damage at the level of the spinal ganglion or dorsal root results in the loss of all sensory modalities in a peripheral distribution pattern.
- Intervertebral Foramen Stenosis: During degenerative spine changes, including decreased intervertebral disc height, the superior articular process of the underlying vertebra may encroach upon the intervertebral foramen. This leads to foraminal narrowing and compression/deformation of the spinal ganglion.