The human spinal column is divided into three parts, based on its curvature and the anatomy of the spinal vertebrae. These are known as the cervical (upper) spine, the thoracic (middle) spine, and the lumbar (lower) spine. Of these sections, the cervical spine consists of the seven vertebrae of the neck (named C1-C7 for convenience with C1 located uppermost). The thoracic region has twelve vertebrae (T1-T12) and the lumbar five (L1-L5).
The cervical spine is the first part of the spinal vertebrae to bear the weight of the skull, and is also responsible for allowing the movement of the head and neck as well as protecting the nerves of the upper spinal column. The cervical vertebrae are smaller and lighter than the other parts of the spinal skeleton to allow for the ease of movement required in this portion of the back. The remainder of the spine is much less flexible than the cervical region, as the lower back is built more for support than to provide a wide range of motion. Whereas the ability for the head and neck to move is clearly advantageous for human vision and communication, it does leave this area more likely to be prone to injuries such as whiplash, which occurs through violent movement of the neck and head, causing overextension of spinal ligaments in that area.
C1, the uppermost vertebra of the spinal column, is also known as the atlas, since the weight of the skull rests upon it, as the world is said to on the Greek titan of the same name. C2 is called the axis, as it is the pivot on which the C1 vertebra rotates, allowing you to turn your head from side to side. Forward and backward movement (nodding) of the head occurs between the bones of the atlas and base of the skull (occipital bone). Rotation (turning) the head mainly involves the atlas and axis (C1 and C2) vertebrae with a small amount of movement occurring lower down in the spine.
The next four cervical vertebrae, C3 to C6, are relatively similar in size and structure being broader laterally than from back to front, and having two bones which meet to form what’s called the spinous process to the rear (the knobbly parts which can be seen on a person‘s back). Protruding upper ‘lips’ from the main body of the bone fit into the concave lower surface of the vertebra immediately above.
C7 is known as the vertebra prominens on account of its large spinous process. In some cases, this vertebra may give rise to a pair of small ribs.
Each of the upper six cervical vertebrae (C1-C6) has a hole, or foramen, in both of the transverse processes located at the side of the bone, through which blood vessels and bundles of sympathetic and spinal nerves are able to pass. The foramen is absent in the thoracic and lumbar vertebrae.