Protection of the Central Nervous System
The CNS is a vital system when
it comes to allowing the human body to function. Even the
smallest injury can result in terrible physical repercussions.
Thus, the CNS is one of the best protected systems in the human
body. The CNS is primarily protected by both by meninges
and cerebrospinal fluid (CSF)
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MENINGES
The three membranes that cover the brain and spinal cord.
The three layers
are the dura mater,
arachnoid, and pia mater
Dura mater- The thick superficial membrane of the meninges. It also serves at the internal periosteum in the cranium. In parts of the dura mater, the double layers are separated by sinuses, large blood vessels. The vessels are responsible for draining the blood that leaves the brain and directing it to the jugular veins.
The dura mater breaks up into four sections:
| Falx Cerebri | The most spacious of the four compartments. The falx cerebri is located between the cerebral hemispheres. It then attaches to the crista galli located on the ethmoid bone |
Tentorium Cerebelli |
The tentorium cerebelli is located between the cerebellum and the posterior section of the cerebrum |
| Epidural space | The epidural space is located between the bone and the dura mater |
| Subdural space | The subdural space functions to separate the dura mater from the arachnoid in the spinal cord and cranial areas of the human body |
Arachnoid- is a thin medial layer of the dura
mater. Arachnoid connects to the innermost layer of the dura
mater, the pia mater by allowing projections to unite to two
sections of the dura mater. In the area between the arachnoid and
pia mater exists the subarachnoid space which houses
cerebrospinal fluid.
Pia mater- is the thin and most deep layer of the
dura mater. The Pia mater lies extremely close to the brain and
outlines every detail of the concave and convex brain tissue.
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CEREBROSPINAL FLUID
The cerebrospinal fluid
serves as a cushion to the floating brain. It consists of 99%
water and a 1% mix of glucose, proteins, urea and salts. Around
135 mL of CSF surrounds fills the ventricles of the brain, and
subarachnoid space surrounding the brain and spinal cord.
Capillary networks called the choroids plexuses are responsible
for producing the bulk of the bodies CSF supply. Once CSF is
produced it circulates through the ventricles in an inferior
motion. As the CSF enters each ventricle more fluid is added. The
cerebrospinal fluid divides paths so that some travels superiorly
to the brain while some moves inferiorly to fill the subarachnoid
space. The cerebrospinal fluid then proceeds to be reabsorbed
into the blood by means of arachnoid granulations. Arachnoid
granulations protrude into the large sinuses present within the
dura mater. The production and reabsorption processes occur at
around the same rate to ensure homeostasis in the body.
The cerebrospinal fluid
serves two main purposes in protecting the structures in the CNS.
First, it is designed to cushion the delicate brain and spinal
cord. Fluids do not compress to a large degree, thus when the
head in jolted the cerebrospinal fluid is present to absorb the
shock and prevent damage from direct contact with the cranial
bones. It similarly protects the spinal cord from a direct
collision with its bony encasement. CSF also functions to act as
a mediator for the trade of nutrients and waste between the blood
and the brain. Cerebrospinal fluid also dissolves and carries
substances removed from the blood through filtration.
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