The upper back is home to the thoracic vertebrae. These 12 vertebrae—along with others above it and below it —help protect the spinal cord, which is a long tube of nervous tissue connected to the brain. Because the spinal cord ends at the third or fourth lumbar vertebra in the lower back, the thoracic vertebrae contain the longest section of the spinal cord. The brain and spinal cord make up the central nervous system of the human body.

As the spinal cord travels down the back from the brain, it branches to extend throughout the body — to the tip of each finger and toe. The spinal cord consists of two tracts: the ascending and the descending. The ascending tract receives sensory information from nerves and sends it to the brain. The brain sends messages to the body via the descending tract. These messages tell muscles what they should do.

In addition to the vertebral column, membranes called meninges also protect the spinal cord by enveloping them and enclosing a protective fluid called cerebrospinal fluid, commonly known as spinal fluid. This fluid helps protect the spine from shocks and other types of damage. It also acts as a transport system for nutrients to keep the spinal cord healthy.

The spinal cord, like the brain, has three meningeal membranes:

  • Dura mater, the outermost layer
  • Arachnoid mater, the middle layer
  • Pia mater, the innermost layer closest to the spinal cord

The thoracic nerves, those extending from the thoracic vertebrae, branch through the body to aid the organs and glands in the abdomen, torso, neck, and head. These nerves are part of the autonomic nervous system, or the system that controls functions such as heart rate, respiration, and other actions that do no require conscious thought.

Important branches of the thoracic nerves include:

  • Intercostal nerves: These nerves travel to the shoulder, upper arm, and parts of the chest, abdomen, sternum, and groin.
  • Subcostal nerve: The last nerve of the thoracic nerve, this acts as a communication point with the lumbar nerves.