The spine, one of the most important of the structures in the body, allows a person to keep upright, stand, move about freely and bend. It also protects the spinal cord, which is made of millions of nerve fibers that connect the brain with the rest of the body.
The spinal column is divided into three main sections: the cervical (upper) spine, the thoracic (middle) spine, and the lumbar (lower) spine.
Cervical (Upper) Spine
This segment of the spinal column is made up of the first 7 vertebrae in the spine. It starts just below the skull at the top of the neck and ends just above the mid-back area. It is the most mobile section of the spine. The nerves of the cervical spine branch off to the upper chest and the arms.
Thoracic (Middle) Spine
This segment of the spinal column, the middle part of the back, consists of 12 vertebrae that connect the ribs and form the part of the back wall of the ribcage area between the neck and the diaphragm. This part of the spine and body is structured in a way that limits the amount of spinal movement compared to the cervical or lumbar segments of the spine. The nerves of the thoracic spine branch off to the chest and abdomen.
Lumbar (Lower) Spine
This segment of the spinal column is often called the lower back. It usually consists of five vertebrae. At the base of the lumbar spine is the sacrum, a fusion of many bones that connects the spine to the pelvis. Sometimes one of the bones of the sacrum will form as a separate vertebra rather than being part of the sacrum. This sixth, or transitional, vertebra that some people have in their lumbar spine normally does not cause any problems. Because the lumbar spine is connected to the pelvis where most weight bearing and body movement takes place, some people seem more prone to lower back pain. The nerves of the lumbar spine region branch off to the legs, pelvis, bowel and bladder.
Parts of the Spine
The individual parts of the spine make it a complex mechanism. The spine consists of bones, called vertebrae, and ligaments and muscles that connect the bones to form the spinal column. Other structures of the spine include the intervertebral discs, facet joints, spinal cord, nerve roots, neural foraminae, paraspinal muscles and spinal segments.
The vertebrae are the 24 individual bones of the spine. The body of each vertebra is a large, round portion of bone, and each vertebra is attached to a bony ring. In essence, the vertebrae are stacked on top of each other, and their rings create a hollow tube to hold and protect the spinal cord.
Intervertebral discs are soft, gel-like cushions between the vertebrae. These discs absorb pressure and help keep the bones of the vertebrae from rubbing against each other.
The joints of the spine, the facet joints, connect the vertebrae to each other and give the spine its flexibility. The two facet joints of each vertebra (one on each side) overlap with neighboring vertebra’s facet joints. Without these joints, the spine would not be able to bend or twist.
Spinal Cord and Nerve Roots
The spinal cord is a column of millions of nerve fibers that carry messages from the brain to the rest of the body. The nerves control the body’s organs and parts, and allow a person to control his or her muscles.
The nerve fibers of the spinal cord branch off in pairs, called nerve roots, at different places in the spine to connect to specific parts of the body. The nerves of the cervical spine go to and control the upper chest and the arms. The nerves of the thoracic spine go to and control the chest and abdomen. The nerves of the lumbar spine go to and control the legs, pelvis, bowel and bladder. Damage to the spinal cord can cause paralysis in certain areas of the body and not in others, depending on which nerve roots are affected.
The neural foraminae are the small openings on each side of the vertebrae where the pairs of nerve roots exit the spinal column to connect to specific areas of the body.
Paraspinal muscles are the many muscles next to the spine. They support the spine and cause the spine to move. Each muscle controls some part of the movement between the vertebrae and the rest of the body.
A spinal segment is a term given to an individual grouping of parts of the spine. One spinal segment consists of two vertebrae attached by ligaments, the disc between the vertebrae, the facet joints that connect the two vertebrae and the neural foraminae between the two vertebrae.