The spinal columnThe vertebral column called the backbone or spine is a column which extends from skull to pelvis, consisting of 33 bones(vertebra) stacked on top of each other. These bones are separated by spinal discs and houses the spinal cord in its spinal canal along its length.
These vertebrae is divided into 5 groups,
Cervical: 7 vertebrae (C1–C7) in the neck
C1 is known as "atlas" and supports the head, C2 is known as "axis"
They are Small-bodied
Thoracic: 12 vertebrae (T1–T12)
They are characterized by small pedicles, long spinous processes, and relatively large intervertebral foramen (neural passageways)
Ribs form from each of the thoracic vertebra(except T11 and T12)
Vertebral body is intermediate in size between the cervical and lumbar vertebrae
Lumbar: 5 vertebrae (L1–L5)
Has a large body and bear the bulk of body weight.
No ribs are attached to them
Longer pedicles, and large intervertebral foramen,
Sacral: 5 vertebrae (S1–S5).
Usually they are fused to from one Sacral bone.
Coccygeal: 4 vertebrae.
Fused to form one bone called Tailbone or coccyx
Functions of the spine
Structural support, balance and flexibility (bending, twisting etc) of the human body.
Protection to spinal cord and spinal nerves and several internal organs
A place of attachment for ribs, several muscles, tendons and ligaments
Curvature of spine
The curvature of spineWhen viewed from back, the spinal column should be straight with no curvature towards any side.
When viewed laterally (from side) the vertebral column presents several curves, which correspond to the different regions of the column.
Cervical curve: A convex forward curve at the cervical (neck) region. This is called 'cervical lordosis'
Thoracic curve: Concave forward curve, which begins at T2 till T12. This is called 'thoracic kyphosis'
Lumbar curve: Another convex forward curve, at the lumbar region. This curve is more prominent in females. This is called a 'lumbar lordosis'.
Pelvic curve: The pelvic curve begins at the sacrum and ends at the point of the coccyx; its concavity is directed downward and forward.
The thoracic and pelvic curves are termed 'primary curves', because they alone are present during fetal life. The cervical and lumbar curves are compensatory or secondary, and are developed after birth, the former when the child is able to hold up its head (at three or four months) and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk.
Characteristics of a vertebra
A typical single vertebra consists of two essential parts., an anterior(front) segment which is called the body, and a posterior(back) segment, which is called the vertebral arch; these enclose a foramen(hole) which is called, the vertebral foramen, through which the spinal cord run.
The vertebral arch consists of a pair of pedicles and a pair of lamiae, and supports seven processes(bony projections), four articular, two transverse, and one spinous.
When these vertebrae are articulated with each other they form a strong pillar for the support of the head and trunk, and the vertebral foramen constitute a canal for the protection of the spinal cord.
While between every pair of vertebrae are two apertures, the intervertebral foramen, one on either side, for the transmission of the spinal nerves and vessels.
Body : The body is the largest part of a vertebra, and is more or less cylindrical in shape. Its upper and lower surfaces are flattened and rough, and each presents a rim around its circumference. In front, the body is convex from side to side and concave from above downward. Behind, it is flat from above downward and slightly concave from side to side. Its anterior surface presents a few small apertures, for the passage of nutrient blood vessels; on the posterior surface is a single large, irregular aperture, or occasionally more than one, for the exit of the vertebral veins from the body of the vertebra.
Pedicles: The pedicles are two short, thick processes, which project backward, one on either side, from the upper part of the body. They are the part of vertebral arch which connects to the vertebral body.
Laminae :The laminae are two broad plates directed backward and medialward from the pedicles. They fuse in the middle line posteriorly, and so complete the posterior boundary of the vertebral foramen.
Spinous Process :The spinous process is directed backward and downward from the junction of the lamina, and serves for the attachment of muscles and ligaments. They can be felt by fingers as bony projections along the back bone.
Articular Processes: The articular processes, two superior and two inferior, spring from the junctions of the pedicles and laminae. The superior project upward, and their articular surfaces are directed more or less backward; the inferior project downward, and their surfaces look more or less forward. The articular surfaces are coated with hyaline cartilage.
Transverse Processes: The transverse processes, two in number, project one at either side from the point where the lamina joins the pedicle, between the superior and inferior articular processes. They serve for the attachment of muscles and ligaments.
Intervertebral Disks
Intervertebral discs (or intervertebral fibrocartilage) lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.
Discs consist of an outer region called 'annulus fibrosus', which surrounds the inner region called 'nucleus pulposus'. The strong outer region distribute pressure evenly across the disc.
The nucleus contains loose fibers suspended in a mucoprotein gel the consistency of jelly and acts as a shock absorber, absorbing the impact of the body's daily activities and keeping the two vertebrae separated.
