Vertebrae (singular: vertebra) are the individual bones that make up the vertebral column (aka spine), is a flexuous and flexible column.
There are thirty-three (33) vertebrae in humans, including the five that are fused to form the sacrum and the four coccygeal bones.
The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy.
This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another.
The number of cervical vertebrae is, however, very rarely increased or diminished.
With the exception of the first and second cervical, the true or movable vertebrae (the upper three regions) present certain common characteristics which are best studied by examining one from the middle of the thoracic region.
A typical vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part – the vertebral or neural arch – which encloses the vertebral foramen.
The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous.
When the vertebrae are articulated with each other, the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord or spinal column), while between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels.
Two transverse processess and one spinous process are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out the left, and one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin.
Superior and inferior articular facets on each vertebra act to restrict the range of movement possible.
Note: For more detailed information, see Cervical vertebrae
These are generally small and delicate. Their spinous processes are short (with the exception of C7 which has the first palpable spinous process), and often split. Numbered top-to-bottom from C1-C7, atlas (C1) and axis (C2), are the vertebrae that allow the neck so much rotation. Specifically, the atlas allows the skull to move up and down, while the axis allows the upper neck to twist left and right. The axis also houses the first intervertebral disk of the spinal, which ends in the sacrum.
Note: For more detailed information, see Thoracic vertebrae
Their spinous processes point downwards, and are long relative to those in other regions. They have surfaces that articulate with the ribs. Some rotation can occur between the thoracic vertebrae, but their connection with the rib cage prevents much flexion or other excursion.
Note: For more detailed information, see Lumbar vertebrae
These vertebrae are very robust in construction, as they must support more weight than other vertebrae. They allow significant flexion and extension, moderate lateral flexion (sidebending), and a small degree of rotation. The discs between these vertebrae create a lumbar lordosis (curvature that is concave posteriorly) in the human spine.