Spinal Nerves: Types, Numbers, Distribution, and Plexuses

Spinal nerves are mixed nerves carrying sensory, motor, and autonomic fibers. There are 31 pairs emerging from the spinal cord, named by region:

• 8 Cervical (C1–C8)
• 12 Thoracic (T1–T12)
• 5 Lumbar (L1–L5)
• 5 Sacral (S1–S5)
• 1 Coccygeal (Co1)

Branches

Each spinal nerve divides into two primary rami:

1. Dorsal (Posterior) Ramus: Innervates deep back muscles and skin of the posterior trunk.
2. Ventral (Anterior) Ramus: Innervates limbs, anterolateral trunk, and forms major plexuses.

Major Plexuses

• Cervical Plexus (C1–C4): Neck, diaphragm (phrenic nerve).
• Brachial Plexus (C5–T1): Upper limb.
• Lumbar Plexus (L1–L4): Lower abdomen, thigh.
• Sacral Plexus (L4–S4): Pelvis, posterior thigh, leg, foot (includes sciatic nerve).

These plexuses give rise to peripheral nerves that supply the body wall and limbs.