The spinal cord contains 31 pairs of segmentally organized spinal nerves. Overall, from the spinal cord emerges eight cervical, twelve thoracic, five lumbar and five sacral spinal nerve pairs and a single coccygeal spinal nerve pair.

They exit the vertebral canal through the intervertebral foramina formed between two adjacent vertebrae. The spinal nerve is attached to the spinal cord with two roots named the ventral and dorsal roots that each contain different fibers.

Ventral (anterior) root - exit the spinal cord through the anterolateral sulcus; contains efferent (motor) fibers;
Dorsal (posterior) root - enters the spinal cord through the posterolateral sulcus; contains afferent (sensory) fibers.

Near the spinal cord, the dorsal root has a bulge called the dorsal root ganglion containing cell bodies of sensory neurons. Both roots merge and form the spinal nerve laterally from the dorsal root ganglion.

Note: Afferent fibers head towards the central nervous system (CNS). Efferent fibers are directed away from the CNS and spinal cord to the periphery of the body.

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Spinal nerves and roots