The spinal cord: the body’s message route

The spinal cord forms part of the central nervous system alongside the brain. It runs through the vertebral canal, protected by the bones of the spine, layers of tissue called meninges, and cerebrospinal fluid. Although the brain interprets much of the information, the spinal cord can coordinate some rapid responses without waiting for a conscious decision.

Neuronal pathways in the spinal cord

Ascending pathways carry sensory information towards the brain. Depending on the pathway, the message may describe touch, pressure, temperature, pain, or the position of a limb. Descending pathways carry movement-related instructions from the brain to motor neurons lower in the nervous system.

Many pathways cross from one side of the nervous system to the other. This crossing is called a decussation. It helps explain why some information from the left side of the body is processed by the right side of the brain, and vice versa.

Protection and anatomy

The vertebrae form a series of openings that create the vertebral canal. This bony channel surrounds the spinal cord, while cerebrospinal fluid helps cushion the nervous tissue. Three meninges also surround the cord: the dura mater, arachnoid mater, and pia mater.

The spinal cord itself is organised into regions that match levels of the spine: cervical, thoracic, lumbar, sacral, and coccygeal. These regions give rise to pairs of spinal nerves that connect the central nervous system with the body.

Spinal nerves and plexuses

Spinal nerves are mixed nerves: they contain sensory fibres travelling towards the central nervous system and motor fibres travelling out towards muscles. In several areas, branches from different spinal nerves join into networks called plexuses.

• Cervical plexus: contributes to sensation and movement in the neck and connects with the nerve supply of the diaphragm.
• Brachial plexus: supplies much of the shoulder, arm, and hand.
• Lumbar plexus: contributes to nerve supply in the lower back, pelvis, and front of the leg.
• Sacral plexus: supplies parts of the pelvis and lower limb, including the route of the sciatic nerve.

Inside the spinal cord

In cross-section, the central grey matter is often described as butterfly-shaped or H-shaped. It contains many neuron cell bodies and is surrounded by white matter, which contains myelinated nerve fibres travelling up and down the cord.

The dorsal horns receive much sensory information. The ventral horns contain motor neuron cell bodies. At some levels, lateral horns contain neurons involved in autonomic control. A small central canal runs through the middle of the cord.

At each level, a dorsal root carries sensory information into the cord, while a ventral root carries motor information out. The dorsal root ganglion contains the cell bodies of many sensory neurons. When the roots join, they form a mixed spinal nerve.

Related terms

To continue, explore spinal nerves, ascending spinal tracts, descending spinal tracts, and reflex actions.