Makeup and mechanics of the spine

The spine is one of the most important components of the human body. It is responsible for maintaining posture and is required to withstand compression forces, twisting, bending, and other motions. Because of all the functions and support the spine needs to provide, it is often susceptible to injury, and when it does become injured, the negative symptoms can be severe.

The Anatomy of the Spine
The spine runs from the pelvis near the hips all the way up to the skull, and it is divided up into four separate sections: the cervical spine, the thoracic spine, the lumbar spine, and the sacrum. The first three of these sections are all composed of separated vertebrae, while the sacrum is composed of a few vertebrae that are all fused together.

Cervical Spine
The cervical spine is composed of seven vertebrae, which are numbered from one to seven from top to bottom. The cervical spine is in a lordotic shape, meaning that it curves inward. When looking at a person from the side when they are facing to your left, the spine will make a “C” shape. The top two vertebrae have slightly different anatomy than the other vertebrae in the spine.

C1, the top vertebrae, is known as the atlas. It has two indentions on the top surface that allow it to fit into the bottom of the skull. C2, called the axis, contains a point, known as the dens, that sticks up from the rear of the vertebrae. The dens work in conjunction with the atlas to allow the head to turn to the right and left.

Thoracic Spine
The thoracic spine is directly under the cervical spine, and it is made up of 12 vertebrae. Similar to the cervical spine, the thoracic spine is also numbered from one to 12 from top to bottom. However, instead of a lordotic shape, the thoracic spine is in a kyphotic shape. This means that it curves outwards, in the shape of a backwards “C.”

Lumbar Spine
The lumbar spine is composed of five vertebrae, which are also numbered from top to bottom from one to five. These are the largest vertebrae in the spine and are forced to support the most weight out of any of the spinal sections. The lumbar spine also has a lordotic curve.

Sacrum
The sacrum is composed of five vertebrae that become fused together during the growing process inside the uterus. This section forms the lower portion of the spine and the back of the pelvis and hip girdle. At the base of the sacrum is a small, pointy bone called the coccyx. This is also known as the tailbone.

The Vertebrae
Vertebrae have a number of features that allow them to perform specific functions. With the exception of the axis and atlas, the other vertebrae all have the same layout. Each vertebra has a spinous process on the back of it. These downward-pointing ridges are able to be felt when you feel the back of your spine.

Transverse processes are found on the left and right sides of each vertebra, and they provide attachment points for tendons and ligaments. There are also facet joints on the top of each vertebra, allowing them to fit onto the vertebra above. These joints allow the spine to twist and bend while remaining stable. The vertebrae get continually larger in size as you move down the spine.

Intervertebral or Spinal Discs
Between each of the vertebrae are spinal discs. These discs serve as cushions between each vertebra and are composed of a tough, fibrous outer layer known as the annulus and a gel-like inner layer known as the nucleus pulposus. These discs help to withstand forces from compression, bending, and twisting.

Spinal Disorders
There are a number of injuries that can occur in the spine, and each one affects the spine differently. Injuries can affect the shape or alignment of the spine, its function, or the size of the discs between each vertebra.

Compressed Vertebra
A vertebral compression fracture, also known as a compressed vertebra, occurs when the bone of a vertebra collapses. This can result from either a compression injury or just a simple movement. These injuries are especially common in individuals who suffer from osteoporosis or in people who suffer from another spinal disorder, such as kyphosis, which is an overly outward bend of the thoracic spine.

Disc or Annular Tear
An annular tear occurs when the outer portion of the spinal disc develops a tear in it. The annulus of the disc contains many nerve fibers, so a tear to this area can be extremely painful. These injuries can heal over time, but scar tissue often forms, resulting in a weaker disc that is more susceptible to future injuries.

Slipped or Herniated Disc
A herniated disc, also known as a slipped disc or compressed disc, occurs when some of the inner portion of the disc leaks out through a tear in the outer portion. This rupture can place pressure on surrounding nerves and cause pain or numbness in the extremities. A slipped disc can also reduce the total height of the disc, which can lessen the spine’s ability to withstand compression.

Degenerated Disc
Discs can break down over time, which occurs due to degenerative disc disease. Over time, the annulus and the nucleus pulposus can become more rigid, causing your spine to have more difficulty bending and twisting. A degenerated disc can become dried out and cracked, leading to less functionality and increased pain.