Basic Spinal Cord Anatomy
The spinal cord is soft – almost jelly like. It is protected by the spinal column which is made up of 33 bones called vertebrae. There is a circular opening in each vertebra similar to the hole in a donut. The bones are stacked one on top of the other and the spinal cord runs through the hollow channel created by the holes in the stacked bones.
Vertebrae are grouped into sections. They are named and numbered from top to bottom according to their location along the backbone:
Cervical vertebrae 1-7: from the base of the skull to the bottom of the neck
Thoracic vertebrae 1-12: the upper back (attached to the ribcage)
Lumbar vertebrae 1-5: the lower back
Sacral vertebrae 1-5: the hip area
Coccygeal vertebrae 1-4 fused: in the tailbone
Although the hard vertebrae protect the soft spinal cord from injury most of the time, the spinal column is not all hard bone. Between the vertebrae are discs of semi-rigid cartilage. In the narrow spaces between the discs are passages through which the spinal nerves exit to the rest of the body. These are places where the spinal cord is vulnerable to direct injury.
Like the vertebrae, the spinal cord is also grouped into segments and named and numbered from top to bottom. Each segment marks where spinal nerves emerge from the cord to connect to specific regions of the body. Locations of spinal cord segments do not correspond exactly to vertebral locations, but are roughly equivalent.
Cervical spinal nerves (C1 to C8) control signals to the back of the head, neck and shoulders, arms and hands, and the diaphragm.
Thoracic spinal nerves (T1 to T12) control signals to the chest muscles, some muscles of the back, and parts of the abdomen.
Lumbar spinal nerves (L1 to L5) control signals to the lower parts of the abdomen and back, buttocks, some parts of the external genital organs, and parts of the legs.
Sacral spinal nerves (S1 to S5) control signals to the thighs and lower parts of the legs, feet, most of the external genital organs, and area around the anus.
The single coccygeal nerve carries sensory information from the skin of the lower back.
(Image: MRI of a cross-section of the spine)