[D]

Go Back to OPVA Hospital Program Page

Basic SCI Anatomy

For More Information contact: OPVA Hospital Liaison

To understand a spinal cord injury, it's helpful to learn the basics of spinal cord anatomy. Together, your brain and spinal cord make up your central nervous system (CNS). For all its importance, the cord is quite small--only about as big around as a pencil. Your spinal cord begins at the lower part of your brain and runs down the center of your back to the tip of your tailbone.

The spinal cord is a ropy bundle of nerves that connects your brain with the rest of your body. How? Think of your spinal cord as a major phone system. All along the cord, at certain intersections, pairs of nerves meet. Some nerves carry sensory messages (like heat or pain) up the spinal cord to the brain. Others shuttle messages from the brain down your spinal cord to your body's muscles and glands.

There are 31 pairs of spinal nerves and roots, divided into basic regions. Eight pairs of cervical nerves (called C1-C8) meet high in your spine, near your neck and shoulders. Twelve thoracic (T1-T12) nerve pairs meet along the middle part of your spine. Further down, 5 lumbar (L1-L5) and 5 sacral (S1-S5) nerve pairs connect. Last, one pair of coccygeal (Co) nerves meets in your tailbone area.

Because these nerves are extremely sensitive, they must be protected. A bony vertebral column (your backbone) and layers of protective tissue surround the spinal cord. Each vertebra, or individual ring of bone in the spinal column, is named according to its position. C2, for example, lies just under the second pair of cervical nerves in your spinal cord. The T9 vertebra sits near the ninth pair of thoracic nerves, which meet at the middle of the cord. L5 is near the fifth pair of lumbar nerves. And so on.

Doctors usually refer to a SCI by its location. A patient may be an "incomplete T4-T5 para." That means his or her spinal cord is damaged--but not completely severed--between the fourth and fifth thoracic vertebrae. Your injury's location determines its effect. An injury low in the spinal cord, like the lumbar region, may affect movement in your legs or control of your bladder. An injury in the cervical segment of the spinal cord could affect the muscles that control of hands and fingers, or your diaphragm that helps your lungs breathe or even the muscles that help your blood vessels maintain normal blood pressure.

The various spinal nerves each control certain body parts, as shown below:

C1-C4 nerves control some muscles and skin in your neck, back of head, and diaphragm
C5-C8 nerves affect your neck, shoulders, arms, and hands
L1-L4 nerves help control the skin and muscles in your abdomen
L4, L5, and S1-S3 nerves affect your buttocks, bowels, thighs, legs, and feet
S4, S5, and Co1 nerves affect the skin in the coccyx, or tailbone, region

Researchers often discuss the white matter and gray matter of a spinal cord. The white matter is bundles of nerve fibers that travel the length of your spinal cord. The white color comes from myelin, an insulating, web-like material wrapped around nerve fibers that helps protect them. They form the outer layer of nerve tissue in the spinal cord. Inside the white matter is a smaller portion of gray matter, which are basically nerves running up and down the cord without myelin.

In some injuries, the spinal cord may get severed. More often, though, the cord is pinched, crushed, squeezed or pressured as the surrounding vertebrae or tissues get hurt. The problem is that when nerves in the CNS get damaged, they simply do not reconnect or replace themselves automatically. That's different from the peripheral nervous system, where nerves, such as those in your arm or leg, can grow back, or regenerate after an injury. Today, researchers are hotly pursuing spinal nerve studies. They hope to make SCI less permanent. Refer to the Nerve Regeneration section for the latest news in this research.