Spinal Anatomy Including Transverse Process and Lamina

Bones of the Spine

Back pain diagnosis often includes the name of the part of the spine from which your healthcare provider believes the pain arises. This article is a crash course on the basics of spinal bones.

The spinal column is made of 24 individual vertebrae that go from the skull to the sacrum. 

From head to toe, the cervical spine connects the skull to the thoracic spine and consists of 7 bones called vertabrae, labeled C1-C7.

The thoracic spine has 12 vertebrae labeled T1-T12 and also connect to the ribcage.

The lumbar area contains 5 vertebrae labeled L1-L5 and connects to the pelvis.

The sacrum bone has 5 bones that begin to fuse at about age one, with the fusion complete approximately by age 30.The sacrum connects to the coccyx (also known as the tailbone) to complete the spinal column.

Vertebra

The term 'vertebra' refers to one spinal bone. 'Vertebrae' is the plural form of the word.

A vertebra consists of a cylindrical body in front and a bony ring in the back.

The cylindrical body of the vertebra is a stacking agent; in other words, the spinal column is made up of the 24 vertebrae, which are stacked one on top of the other. This is what gives basic weight support to the spine.

The bony ring is attached to the back of the vertebral body and offer places for spinal muscles and ligaments to attach.

The long tunnel formed by the inside of the rings of all 24 vertebrae is called the spinal canal. This is where the spinal cord passes through.

Nerves branch off from the spinal cord and exit the spine by means of smaller holes on the sides of the bones, called neuralforamina. The neuralforamina are constructed from archways on the sides of the adjacent vertebrae that are stacked together.

The Vertebral Bodies and Intervertebral Discs

The vertebral body is the largest and most supportive part of the vertebra.

As discussed above, the vertebral body is a large roundish structure that provides weight support through the column. The vertebrae stack on top of one another at the vertebral bodies.

In between the vertebral bodies are the intervertebral discs, which are responsible for shock absorption during movement. They do this by acting as a movable cushion between the vertebral bodies.

Common disc problems include disc degeneration and herniated disc. An annular tear is another injury that may lead to a herniated disc, but not always. The intervertebral disc is often the first place in the spine where age-related degenerative changes (which pretty much everyone gets) take place.

The vertebral body defines part of the edge of the central area in the spinal column through which the spinal cord passes. It also contributes to the vertebral endplate, which can be another site of degenerative spinal changes.

The Facet Joint

The facet joint is located on the bony ring in the back of the spinal column. 

It is formed by processes (which are basically extensions of bone) that emanate from an interconnected pair of adjacent vertebrae—one above and below. At each level (called a "segment,") there's a right and left facet joint. This means 4 of these processes participate to construct the facet joints at any one level, or segment, of the spine. The processes that make up the facet joint are called the "articular processes."

The interconnected aspect of facet joint construction makes it a key player for keeping the entire spinal column stable during movement.

Facet joints are also called the zygapophyseal joints. That's a difficult word to pronounce, so many people, including healthcare providers, prefer the term "facet joint."

Problems with facet joints are a very common cause of back pain and generally are associated with spinal arthritis and/or degenerative spinal changes.

Another back problem called spondylolisthesis often starts with a small fracture in an obscure area of the facet joint known as the pars. The initial injury is called a pars defect; it's brought on by repeated spinal movements such as those done by athletes. (Middle-aged people, especially those who are overweight are also at risk for a pars defect).

Left unchecked, a pars defect can develop into spondylosis and finally spondylolisthesis, where one bone becomes destabilized to the point of slipping either forward or back of the bone next to it.

Spinous and Transverse Processes

Similar to articular processes discussed above, spinous and transverse processes are projections of bone that emanate off the bony ring in the back of the vertebral body. Spinous and transverse processes look a little like fingers.

On each vertebra, there are two transverse processes and one spinous process. The two transverse processes are located on either side of the ring, while the spinous process is located in the middle.

These processes provide sites to which back muscles and ligaments attach.

Pedicle

The pedicle is a short projection of bone that comes directly off the back of the vertebral body. The pedicle lies between the back of the vertebral body and the transverse process. There are two pedicles per vertebra, one on each side.

The Lamina

The lamina is the part of the vertebra that connects the spinous process and the transverse process. There are two laminae, located on either side of the spinous process. The lamina is often the site of back surgery when you need to relieve the symptoms caused by pressure on the spinal nerve roots. This can happen in the case of spinal stenosis.

One commonly given surgery is called a laminectomy, but there are others, as well.

The Spinal Nerves and Column

When you count the sacrum and coccyx, the spine is a long flexible column made of 26 interconnected bones. Holes located on the sides of the column (called neuralforamina, discussed above) are made by the interfacing vertebrae; nerve roots exit out these holes, and depending on the condition of the bone around them, they may play an important role in the presence or absence of back pain.

Examples of common back problems involving the spinal nerve root include herniated disc and spinal stenosis.

The spinal cord runs through the center passageway (spinal canal, already discussed) that is made by the bony rings of the stack of vertebrae.

Spinal nerves arise from the spinal cord at each level. The first branch into spinal nerve roots (already discussed) and then further subdivide into nerves that go to all parts of the body to pick up sensory information and relay that to the brain, as well as deliver movement instructions and impulses from the brain to the muscles.

Spinal nerve roots exit the spaces (called intervertebral foramina) created between two adjacent, stacked vertebrae.

The spinal cord ends after the first lumbar (low back area) vertebra. Beyond that, it is a bundle of nerves and roots that are more exposed than the nerves residing above. This bundle is called the cauda equina.