CEREBROSPINAL FLUID (CSF):-
A fluid
produced by ependymal cells that cover choroid plexuses in the ventricles of
the brain, the fluid circulates in the ventricles, the central canal, and the
subarachnoid space around the brain and spinal cord.
1.
Early
during the development of brain in the embryo, the cerebrospinal fluid occupies
the cavities of brain and the spinal cord.
2.
CSF
is secreted by the blood vessels of anterior choroid plexus.
3.
It
is meant for acting as a cushion against shocks or jerks and also a medium for
the movement of nutrients, metabolic waste and exchange of respiratory gases.
4.
It
is a colourless and alkaline fluid which contains water, glucose, creatine,
electrolytes such as chlorides of calcium, sodium and potassium .
5.
The
blood capillaries present in arachnoid mater reabsorb CSF which is returned to
the ventricles of brain and central canal of the spinal cord by the blood
capillaries which form the choroid plexus so that its circulation is made
possible.
Circulation of CSF :-
The CSF
formed in the choroid plexuses of each lateral ventricle flows into the third
ventricle through two narrow,oval openings, the inter ventricular foramina. More
CSF is added by the choroid plexus in the roof of the third ventricle.
v
The
fluid then flows through the aqueduct of the mid brain (cerebral aqueduct)
which passes through the midbrain , into the fourth ventricle.
v
The
choroid plexus of the fourth ventricle contributes more fluid. CSF then
circulates in the central canal of the spinal cord and in the subarachnoid
space around the surface of the brain and spinal cord.
v
CSF
is gradually reabsorbed into the blood through arachnoid villi (projecting into
the dural venous sinuses), especially the superior sagittal sinus.
v
Normally
, CSF is reabsorbed as rapidly as it is formed by the choroid plexuses, at a
rate of about 20 ml/hour (480ml/day).
v
The
rate of formation and reabsorption are the same, the pressure of the CSF
normally is constant.
VENTRICLES OF THE BRAIN
Most
part of the brain is hollow from inside and various cavities are called ventricles. All of them are in continuation with
one another and are filled with cerebrospinal fluid.
The
largest ventricles are those which are present in the cerebrum. There are two
of them which are placed in the form of lateral ventricles as one in each
cerebral hemisphere.
v
The
ventricle lying in the middle of diencephalon is a tubular space called the
third ventricle which is connected on one side with the lateral ventricles via
a narrow passage called inter ventricular foramen or foramen of monro
while on the other end it continues into the fourth ventricle through another
narrow passage called cerebral aqueduct or aqueduct of sylvius or iter
in the substance of the midbrain.
v
The
fourth ventricle is a space in the pons varolii and medulla oblongata.
This ventricle is in continuation with the fluid filled central canal of the
spinal cord.
v
The
cerebrospinal fluid present in the subdural and subarachnoid spaces around the
brain comes from the fourth ventricle through three different apertures in the
root of this ventricle. Out of them one is a median aperture while two are
lateral apertures.
Ø
Cerebrospinal
fluid is formed in the choroid plexuses and circulates through the lateral
ventricles, third ventricle, fourth ventricle, subarachnoid space, and central
canal. Most of the fluid is absorbed
into the blood across the arachnoid villi of the superior sagittal
sinus.
Ø
CSF
provides mechanical protection, chemical protection, and circulation of
nutrients.
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