Spinal ganglion

Where is it located and how is it formed?

The spinal ganglion is located on the posterior root (radix posterior / dorsalis) of the spinal cord, which consists predominantly of afferent (sensory) nerve fibers.

The posterior root joins the anterior (motor) root laterally to the spinal ganglion. This fusion forms the mixed trunk of the spinal nerve (truncus nervi spinalis), containing both sensory and motor fibers.

Histological structure

Microscopic examination with hematoxylin and eosin staining reveals pseudounipolar neurons of the spinal ganglion.

Each such neuron has:

• Peripheral process — travels toward the receptors.
• Central process — enters the spinal cord as part of the posterior root.

What pathways does it participate in?

Cells of the spinal ganglion act as the first neuron (I) for ascending sensory tracts and reflex arcs:

• Anterior spinothalamic tract (tractus spinothalamicus anterior) — conducts tactile sensation (touch, pressure). Signals originate from peritrichial nerve endings and tactile corpuscles.
• Lateral spinothalamic tract (tractus spinothalamicus lateralis) — conducts pain and temperature sensitivity.
• Spinocerebellar tracts — the anterior tract of Gowers and the posterior direct tract; they conduct unconscious proprioceptive sensation from muscle and tendon receptors to the cerebellum.
• Simple somatic reflex arc — the ganglion serves as the afferent link for tendon reflexes, including the knee-jerk reflex. Signals from muscle spindles pass through the ganglion to motor neurons in the anterior horns.

How are fibers distributed upon entering the spinal cord?

The central processes of ganglion cells, upon entering the spinal cord, divide into two groups:

• Medial group — thick, heavily myelinated fibers. They enter the posterior funiculus and bifurcate in a T-shape. Ascending branches form the gracile and cuneate fasciculi, heading toward the medulla oblongata. Descending branches connect with cells of the posterior columns in lower segments. In the thoracic and cervical regions, this fasciculus resembles a comma shape, and in the lumbar region, an oval field.
• Lateral group — thin, lightly myelinated fibers. They travel toward the marginal nucleus and then pass into the posterior column, where they synapse with its cells.

Clinical significance and topography

• Syndrome of lesion: Damage at the level of the spinal ganglion or posterior root leads to the loss of all types of sensation in a peripheral pattern.
• Intervertebral foramen stenosis: In degenerative spinal conditions, including decreased intervertebral disc height, the superior articular process of the vertebra below may project into the intervertebral foramen. This leads to narrowing of the foramen and deformation of the spinal ganglion.

Class and exam questions

What else to study on this topic

• Posterior root of the spinal cord
• Spinothalamic tract
• Spinal nerve
• Simple somatic reflex arc

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.