Spinal Cord and Spinal Nerve Roots

Spinal Cord and Spinal Nerve Roots

nerve roots
Fig 1: Spine nerve roots
(larger view)

disc herniations
Fig 2: Distribution of Disc Herniations
(larger view)

skin innervations
Fig 3: Distribution of Skin Innervation
(larger view)

The spinal cord comes off the base of the brain, runs throughout the cervical and thoracic spine, and ends at the lower part of the thoracic spine. Therefore, spinal cord injury or damage may accompany trauma or diseases of the cervical spine or thoracic spine.

The spinal cord does not run through the lumbar spine (lower back). After the spinal cord stops in the lower thoracic spine, the nerve roots from the lumbar and sacral levels come off the bottom of the cord like a "horse's tail" (cauda equina) and exit the spine (view the spinal nerve roots with Figure 1).

Therefore, because the lumbar spine has no spinal cord and comprises a large amount of space for the nerve roots, even serious conditions (such as a large disc herniation) are unlikely to cause paraplegia (loss of motor function in the legs).

Division of the Spinal Cord

The spinal cord can be divided into segments according to the nerve roots that branch off of it. Nerves along the cord consists of 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve. The nerve roots run through the bony canal, and at each level a pair of nerve roots exits from the spine.

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  • Cervical spine nerve roots. In the cervical spine (neck), the nerve root is named for the lower segment that it runs between (e.g. C6 nerve root at C5-C6 segment).
  • Lumbar spine nerve roots. In the lumbar spine (lower back), the nerve is named for the upper segment that it runs between (e.g. L4 nerve root at L4-L5 segment).

Nerve Irritation from a Herniated Disc

The nerve passing to the next level runs over a weak spot in the disc space, which is the reason discs tend to herniate (extrude) right under the nerve root and can cause leg pain (lumbar radiculopathy or sciatica).


  • Arm pain from a cervical disc herniation is usually accompanied by numbness/tingling and runs to the fingers.
  • Leg pain from a lumbar disc herniation will usually run below the knee, and possibly to the foot, and may be accompanied by numbness. Learn more about how a herniated disc in the lower back can affect the sciatic nerve and lead to leg pain and even foot pain.

Pinched Nerve Pathology


  • Pinched nerve at S1. Impingement of the S1 nerve can lead to weakness with the large gastronemius muscle in the back of the calf, causing difficulty with foot push off (view the distribution of skin innervation with Figure 3). Numbness for the S1 nerve runs on the outside of the foot. The S1 nerve root also supplies innervation for the ankle jerk (tap on the achilles tendon and the foot goes down), and a loss of this reflex indicates S1 impingement, although it does not create loss of function.




Healing from a Pinched Nerve


