The Vertebral Column
The vertebral column is a series of individual segments, the vertebrae, and one
on top of the other.
Motions of the Head
The upper part of the vertebral column, the neck region, and associated muscles
provide the head with its various motions.
The upper two vertebrae are specifically constructed for head motions.
The articulation between the occipital base of the skull and the atlas (the first
cervical vertebra) is specially constructed for anterior-posterior motions of the head
Between the atlas (the first cervical vertebra) and the axis (the second
cervical vertebra) is a special pivotal-type joint. This joint facilitates rotary (turning)
motions of the head.
The vertebral bodies and the associated intervertebral discs are the primary
mechanism for supporting the body weight.
In the lumbar and lumbosacral regions, the articular processes of the
vertebrae is also weight bearing.
A bony projection extends upward and another extends downward from each right and
left side of the neural arch of each of these vertebrae. These projections are the articular processes.
Through them, as well as through the vertebral bodies and discs, adjacent vertebrae are articulated
with each other.
The specially constructed sacrum, at the lower end of the vertebral column,
receives the body weight from above and transfers it to the pelvic bones of the lower
Protection of the Spinal Cord and its Membranes
Whereas the cranium protects the brain, the neural arches protect the spinal cord
and its membranes (meninges).
The neural arches of the individual vertebrae arch over the spinal cord and its membranes.
The continuous series of neural arches forms a continuous spinal canal.
Motion of the Vertebral Column
Together, the vertebrae, the intervertebral discs, and the associated ligaments
form a semiflexible rod.
This allows a certain amount of motion to the vertebral column
in addition to its supporting role.
The spinous and transverse processes of the neural arches serve as attachments
for skeletal muscles. By acting as levers, these processes enable the skeletal muscles
to move the vertebrae.
Role of Intervertebral Discs - Motion
The intervertebral discs between adjacent vertebrae allow motion to occur between
adjacent vertebrae. The relative thickness of the individual intervertebral disc determines
the amount of motion possible between the adjacent vertebrae.
The total movement of the vertebral column (spine) is the sum of the motions of the
individual intervertebral discs.
Role of Intervertebral Discs – Shock Absorber
The intervertebral disc acts as a shock absorber. As such, it minimizes the shocks that
are transmitted to the vertebral column by the contact of the heels with the floor during
walking, jumping, and so on.
During the course of a day standing and sitting, the individual becomes
about an inch shorter than he was at the beginning of the day. This is due to
the effects of compression on the discs.
After a good night's rest in a horizontal position, these discs regain their
original thickness. As an astronaut works at zero gravity, he retains his full height.
Diurnal height change is lower in older individuals.
With age, individuals tend to lose height. This is because the intervertebral discs shrink
somewhat over the years. Since these discs also become less flexible, there is less compression
from morning until night. Thus, the height in the evening is closer to the morning height than
with a younger person.
Role of Curvature of Vertebral Column
The vertebral column has four curvatures.
Two of these are concave to the front; two are concave to the rear.
Intervertebral discs also have curvatures.
These curvatures function as shock absorbers for the body.
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