Getting Down to the Bare Bones : The Structural Anatomy, Function and Movement of the Spine

A. Anatomical structure

(1) The vertebral column or spine is part of the axial skeleton and is made up of 33 vertebrae which are divided into 5 regions according to structure and function:

1. cervical region (meaning neck) consisting of 7 cervical vertebrae named C1-C7;

2. thoracic region (equivalent to the thorax of an insect) consisting of 12 thoracic vertebrae named T1-T12;

3. lumbar region consisting of 5 lumbar vertebrae L1-L5;

4. sacral region consisting of the sacrum made up of 5 fused vertebrae; and

5. coccygeal region consisting of the coccyx - 4 fused vertebrae [occasionally this varies from 3 to 5 and the first coccygeal vertebra can be separate].

(2) C1 is also known as the atlas. It is a wide oval shape with no vertebral body or spinous process. There are 2 dents onto which the occipital condyles articulate.

(3) C2, or the axis, has an additional dens or odontoid (tooth-like) process sticking up from the body which articulates just inside the front of the atlas.

(4) Vertebrae C3-C7, T1-T12, L1-L5 all have their bony structure in common, consisting of: vertebral body; vertebral arch; vertebral foramen; superior and inferior articular processes; upper and lower notches; a forked spinous process; and 2 transverse processes.*

(5) T1-T12 have 2 additional facets for the ribs to articulate.

(6) Invertebral discs lie between the bodies of vertebrae C2 down to the sacrum, making up a 1/5 of the spinal length

(7) Spinal curves:

1. From front to back, the cervical and lumbar regions are concave and the thoracic, sacral and coccygeal regions are convex.

2. From the lateral view, the curves in the cervical region are referred to as cervical lordosis, thoracic region – thoracic kyphosis, lumbar region - lumbar lordosis. A lateral curve is called a scoliosis.

3. The thoracic curve is a primary curve developed in the womb. The cervical and lumbar curves are secondary curves, developed at 3 months and 1-2 years respectively.

B. Function and movement

1. the cervical region has the greatest movement, the lumbar more than thoracic;

2. the main functions of the cervical, thoracic and lumbar regions' are to support the head and trunk, provide support for the arms, protect the spinal cord and transmit the weight of the body to the legs.

3. The sacral area joins with the hipbones to form the pelvis. It's main functions are to support the body, transfer body weight to legs and transmit force of leg movements to trunk.

4. The coccygeal region is not weight bearing, but helps ensure stability of the pelvis.

5. Movement ranges are extension, hyper-extension, flexion, lateral flexion and rotation - from small movements in consecutive vertebrae to large movements of the whole spine.

6. Vertebral curvatures can be affected or exaggerated by injury/trauma, pregnancy, obesity, disease, dominant hand or repetitive activities including sport, posture.

*The vertebral foramen and linking superior and inferior articular processes create the spinal canal through which the spinal cord can be accommodated and protected. The upper and lower notches link and create holes for nerves to pass though.

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