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The Backbone - General Structure

The presence of a backbone is the distinguishing feature of a large group of animals which includes fish, amphibians, reptiles, mammals and us.

The backbone is generally referred to as the vertebral column and the individual backbones are called vertebrae (pronounced verterbree or verterbray), a single bone from the back being a vertebra.

The words vertebral and spinal are often used to mean the same thing and are commonly interchangeable.

In people the spinal column is divided into 4 main sections:

  • Cervical - the neck
  • Thoracic - the thorax bearing the ribs
  • Lumbar - the low back
  • Sacral - leading to the coccyx

The spine is divided into 4 sections for several reasons. The different parts of the spine have a curve which faces in a particular direction.

In the thoracic spine, the vertebrae all look similar to a great extent, so they are all put into one section, and this applies to a greater or lesser extent in the other areas of the spine. The various parts of the spine tend to specialize in particular directions of movement and have different functions in the life of the spine.

The Cervical Spine

There are seven cervical vertebrae in the necks of all mammals from bats to whales to giraffes to us.

In humans the vertebrae are named from the top downwards as C1, C2,….C7.

C1 and C2 are quite different from the remaining five vertebrae in the neck. The C1 is called the atlas, after the mythical greek character Atlas, who held the world on his shoulders. Our C1 only has to hold our heads but the head is heavy so the atlas’ job is important. The atlas is the only vertebra which does not have a solid central body.

Below the atlas is the C2 vertebra or axis, which has a spike projecting upwards to make a joint with the atlas above. This spike is called the dens (tooth) and is actually the central body of the atlas which has been “captured” by the axis below.

The rest of the cervical vertebrae, C3 to C7, look more normal and like each other. The upper neck specializes in rotation so we can turn the head, the lower neck in forward and backward moving.

The Thoracic Spine

There are twelve thoracic vertebrae, named from T1 at the base of the neck to T12 about three-quarters the way down the back. These vertebrae all look relatively similar. The thoracic spine allows a considerable amount of rotation but little forward and backward movement.

Each of the thoracic bones bears a pair of ribs. Because the rib cage is relatively rigid and the heart and lungs are inside it, this area of the spine does not allow much movement except rotation.

The Lumbar Spine

 

There are normally five lumbar vertebrae, although people may have 4 or 6 in certain cases, depending on the way they are counted.

Many “abnormalities” on x-ray are of no importance in terms of pain or disability.

The lumbar vertebrae are bigger and more solid than the ones above as they have to take more of the body’s weight. The vertebrae are named from L1 above to L5 at the bottom of the mobile spine.

The Sacrum and coccyx

The sacrum is a solid block of bone situated between the sides of the pelvis. It sits like an upturned triangle. It is formed by 5 sacral vertebrae which have fused together to form a single piece of bone.

The coccyx is at the very bottom of the spinal column and usually made up of 4 rudimentary (not fully formed) vertebrae, but the number varies from 3 to 5.

 


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