The spinal cord is basically a bundle of nerves that runs from the brainstem down the back.

At 31 points, pairs of spinal nerves branch off to specific areas of the body. Starting at the top of the spine, there are:

• Eight nerve pairs branching off from the cervical section (C1 to 8)
• 12 from the thoracic region (T1 to 12)
• Five from the lumbar spine (L1 to 5)
• Five from the sacral area (S1 to 5)
• And one from the coccyx at the base of the spine, known as the coccyxgeal nerve.

Also contained in the spinal cord are local neuron loops that don’t require input from the brain. These are known as reflex arcs and control some of the body’s most basic involuntary reactions. Of these, probably the best known is the leg bounce caused by tapping a specific area just below the front of the knee, but reflex responses can be more complicated and learned, for example not having to think about riding a bike once the skill has been acquired.