The spinal cord is the
portion of the central nervous system enclosed in the vertebral column. It
extends vertically along
the body and has a central canal . It is very difficult to differentiate the
spinal column from the brain by a definite line; one is like the extention
of the other. In general, it extends till the lowest side of the first
lumbar vertebra in adults.
The end part consists of a
bundle of nerve fibres formed in the shape of a horse tail.
When a transverse section of the spinal column is
examined from outside towards the inside the following can be seen:-
A vertebra made of bone tissue, underneath lies the
durameter (hard membrane), beneath it lies the arachnoid (the membrane which
looks like a spider ), followed by the cerebro spinal liquid, which is also
found in the brain. Beneath this cerebro spinal liquid there lies the pia
mater (the thin membrane made up of arachnoid
mater, then comes the layer of white matter followed by the layer of grey
matter. Last of all, the central canal which is filled with cerebro spinal
liquid can be seen.
In the spinal cord, the central canal is surrounded
by grey matter, outside which there is a lighter region that is covering the
grey region too.
The white matter of the spinal cord is made up of
nerve axons.
The white matter consists of sensory nerve bundles
and bundles of sensory
intermediary nerves that lie along the spinal cord.
In general, the latter ones end up in the brain.
The rest of the white matter contains the motor nerves that go from
the brain to all the organs of the body.
The grey matter takes its colour from the main body
of the neurons. It is seen in
the transverse section that the grey matter is making an ‘’H’’
shaped column vertically along the spinal cord.
There is a continuous electrical flow between the
brain and the receiving organs through a line which is in the form of
stairs. Through this line, the
impulses are carried to and from the brain continuosly.
When certain parts through this line are broken off , then this will
stop the sensory nerves from transmitting to the brain through the spinal
cord. Therefore, any impulse given to any part of the body below that broken
region would not be perceived by the brain and the brain won’t be able to
activate and control the muscles of that part voluntarily.
There can only be reflexes of
an involuntary type.
The spinal cord is in relation with two important
parts in the region of its connection to the brain. These are the medulla
oblongata and the cerebellum.
The medulla oblongata is found between the spinal
cord and the back part of the brain. The grey column of the medulla
oblongata extends to the inside of the brain’s medulla.
The medulla oblongata controls the heart beats, the
change in the diameters of the arteries, the respiratory movements, the act
of swallowing and the secretion of saliva.
Also, the act of standing up and the management of
the posture of the body are being made in the centres of this region.
The other important part is the cerebellum.
The cerebellum is found behind the posterior end of
the brain (Cerebrum). Like the brain, it consists of two hemispheres.
All the impulses coming from the receptors in the
sensory organs, and from the parts of the ear which are related to the
balance reach this organ. The
Cerebellum arranges the degree of contraction in the muscles.
If an electrical
stimulus is applied to the Cerebellum it would not
create any muscle movement or any
sensory perception. This
experiment proves that the Cerebellum does not directly stimulate any muscle
annd initiate any movement.
However, when it is taken out, it would cause great defects in the movement
of the muscles. The function of the Cerebellum is to compare and synchronize
the stimulating impulses coming from the muscles with the continuous
impulses coming from the motoric centers of the brain.
In this manner it provides the muscles either
directly or indirectlt with the suitable impulses.
The motorical commands such as speaking are created
by the big brain i.e. the Cerebrum and their copies are sent to the
Cerebellum. The Cerebellum controls the impulses. It sends the realted ones
to the big brain and in some cases directly to the muscles.
So, the Cerebellum is playing an important role in coordinating the
centers of the brain and the reactive organs of the body.
All of us are thinking a lot of things in our
unconscious. However, the the
brain triangle (Corpus Striatum), thalamus, and the Cerebellum and many
other centers of teh brain which we are not aware of are
selecting and censoring these thoughts. It is being assumed
that as a result of this
mechanism, only the thoughts
that are in accordance with the social status of the individual are being
let out.
