●       In humans there are 31 pairs of Spinal Nerves arising on each side of spinal cord through corresponding vertebra.

• 8 Cervical Spinal Nerve pairs (C1-C8)

• 12 Thoracic Spinal Nerve pairs (T1-T12)

• 5 Lumbar Spinal Nerve pairs (L1-L5)

• 5 Sacral Spinal Nerve pairs (S1-S5)

• 1 Coccygeal Spinal Nerve pair

●       Each Spinal Nerve is formed by Dorsal and Ventral Roots. Dorsal Afferent Root carries sensory fibres from body towards spinal cord. Ventral Efferent Root carries motor fibres towards body and muscle from Spinal Cord.

●       Each Spinal Nerve then divides into Dorsal (posterior) Ramus and Ventral (Anterior) Ramus. These Rami then supply the back and rest of the body respectively.

FUNCTION AND SIGNIFICANCE

• Each Spinal Nerve carries signals for muscle control and sensations of skin. Area of skin supplied by one Spinal Nerve is called Dermatome. Muscles supplied one Spinal Nerve constitute one Myotome.
• Injury to any specific Spinal Nerve leads to specific symptoms of that Dermatome or Myotome. It can can manifest as muscle weakness, numbness, tingling sensation or paralysis.