Transverse Process, Lamina and More. Spinal Anatomy for the Rest of Us

1
Bones of the Spine

The spine, ribs, pelvis and sacrum
The spine, ribs, pelvis and sacrum. MedicalRF.com/Getty Images

Back pain diagnosis often includes the name of the part of the spine from which your doctor believes the pain arises. This article is a mini-crash course on the basics of spinal bones, for your reference.

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

The sacrum bone — which is really 5 bones that begin to fuse at about age one, with the fusion complete approximately by age 30 — plus the coccyx bone, complete the spine at the very  bottom of the column. (The coccyx is the name given to the your tailbone.)

At the thoracic and lumbar areas respectively, the spine connects to the ribs and pelvis to make the trunk, or core.

2
Vertebra

Spinal bone, or verebra
Spinal bone, or verebra. MedicalRF.com/Getty Images

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

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

The 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; it has parts that contribute to joint anatomy (which can get complicated, fast.) These parts also offer places for spinal muscles and ligaments to attach.

The spinal cord passes through a large hole in the center of the spinal cord, called the spinal canal. The spinal canal is constructed of the collective inside of the rings of all 24 vertebrae that make up the column.

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

3
The Vertebral Bodies and Intervertebral Discs

Spinal column
Spinal column. MedicalRF.com/Getty Images

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 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 vertebrtal bodies.

Common disc problems include disc degeneration and herniated disc. Annular tear is another injury that may lead to a herniated disc, but not always. By the way, 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 the vertebral end plate, which can be another site of degenerative spinal changes.

4
The Facet Joint

Spinal column with facet joints.
Spinal column with facet joints. MedicalRF.com/Getty Images

The facet joint is located on the bony ring in 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 practitioners, 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 the type done by young athletes who train seriously. (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.

5
Spinous and Transverse Processes

Spinal bone showing transverse and spinous processes.
Spinal bone showing transverse and spinous processes. MedicalRF.com/Getty Images

Similar to articular processes discussed above, spinous and transverse processes are projections of bone that emanate off the bony ring in 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 process 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.

6
Pedicle

Spinal bone with body, bony ring, pedicle and more
Spinal bone with body, bony ring, pedicle and more. MedicalRF.com/Getty images

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.

7
The Lamina

Vertebra or spinal bone
Vertebra or spinal bone. MedicalRF.com/Getty Images

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 side 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.

8
The Spinal Nerves and Column

Spinal column, spinal canal and spinal nerve roots.
Spinal column, spinal canal and spinal nerve roots. MedicalRF.com/Getty Images

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 neuralforamen, 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 disussed) that is made by the bony rings of the stack of vertebrae.

Spinal nerves arise from the spinal cord at each level. They 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 foramen) 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. 

 

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