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8/12/2019 Overview CNS - Drg. Yuni
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Yuniarti
Department of anatomy
Faculty of medicine
UNISBA
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Organization of the nervous system
1.Central Nerve System
- Brain
- Spinal cord
2. Peripheral Nerve System
- Cranial nerve
- Spinal nerve
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Examination of an electron
micrograph of the central nervoussystem shows that the lumen of a
blood capillary is separated from
the extracellular spaces around the
neurons and neuroglia by the
following structures:(1) the endothelial cells in the wall of
the capillary
(2) a continuous basement membrane
surrounding the capillary outside
the endothelial cells
(3) the foot processes of the
astrocytes that adhere to the outer
surface of the capillary wall
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In molecular terms, the blood-brain barrier is thus a continuous lipid
bilayer that encircles the endothelial cells and isolates the brain tissue
from the blood. This explains how lipophilic molecules can readily
diffuse through the barrier, whereas hydrophilic molecules are
excluded.
The structure of the blood-brain barrier is not identical in all regions of the
central nervous system. In fact, in those areas where the blood-brain barrier
appears to be absent, the capillary endothelium contains fenestrations
across which proteins and small organic molecules may pass from the bloodto the nervous tissue
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Characteristics of Cranial Meninges
Dura mater:inner fibrous layer (meningeal layer)
outer fibrous layer (endosteal layer)
Arachnoid mater:
contacts epithelial layer of dura mater,Subarachnoid space and pia mater
Pia mater:attached to brain surface by
astrocytes
However, the cranial dura mater has
two layers; the spinal dura mater has
only one
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Three extension of dura mater separate parts of the
brain :
1. The falx cerebri
Separate the two hemispheres of the cerebrum2. The falx cerebelli
Separate the two hemispheres of the cerebellum
3. The tentorium cerebelli
Separate the cerebrum from the cerebellum
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Of the three meningeal spacescommonly mentioned in relation
to the cranial meninges, only
one exists as a space in the
absence of
pathology
1. The dura -cranium interface
(extradural or epidural space)
is not a natural spacebetween the cranium and the
external periosteal layer of the
dura because the dura is
attached to the bones.
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2. The dura-arachnoid junctionor
interface (subdural space) is likewise not
a natural space between the dura and
the arachnoid. A space may develop in
the dural border cell layer as the result
of trauma, such as after a blow to the
head
3. The subarachnoid space, between the
arachnoid and pia, is a real space that
contains CSF, trabecular cells, cerebralarteries, and bridging superior cerebral
veins that drain into the superior sagittal
sinus
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The ventricles are four fluid-filled
cavities located within the brain, theseare :
~ the two lateral ventricles
There are two large lateral ventricles,
and one is present in each
cerebral hemisphere
The ventricle is a roughly C-shaped
cavity and may be divided into a
body, which occupies the parietal
lobe and from which anterior,
posterior, and inferior horns extend
into the frontal, occipital, andtemporal lobes
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the third ventricle
The third ventricle is a slitlike
cleft between the two thalami
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CSF is a clear, colorless liquid that protects the brain and spinal cord against
chemical and physical injuries
The CSF is found in the ventricles of the brain and in the subarachnoid space
around the brain and spinal cord
CSF has a volume of about 80-150 mL
Rate of production 20mL/hour
Composition : glucose,protein, lactic acid, urea, cation, anion & some white
blood cells
The site of CSF production are the choroid plexus, which are network ofcapillaries in the walls o the ventricle
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The Functions of the CSF
. 1
The cerebrospinal fluid, which bathes the external and internal
surfaces of the brain and spinal cord
Cushions and protects thecentral nervous system from trauma
2
Because the density of the brain is only slightly greater than that ofthe cerebrospinal fluidit provides mechanical buoyancy andsupport for the brain
3
The close relationship of the fluid to the nervous tissue and thebloodenables it to serve as a reservoir and assist in theregulation of the contents of the skull. For example, if the brainvolume or the blood volume increases, the cerebrospinal fluidvolume decreases
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The Functions of the CSF
. 4
cerebrospinal fluid is an ideal physiologic
substrate,t probably plays an active part inthe nourishment of the nervous tissue
5 removal of products of neuronal metabolism
6 Serves as a pathway for pineal secretions to
reach the pituitary gland by circulating throughthe cerebrospinal fluid in the third ventricle
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The sites of CSF production are the
choroid plexuses , networks of bloodcapillaries (microscopic
blood vessels) in the walls of the ventricles
The capillaries are covered by ependymal
cells that form cerebrospinal fluid from
blood plasma by filtration and secretion.
Because the ependymal cells are joined by
tight junctions,
materials entering CSF from choroid
capillaries cannot leak between
these cells; instead, they must pass
through the ependymal
cells.
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There is free passage of water, gases, and lipid-soluble substances from the
blood to the cerebrospinal fluid.
Macromolecules such as proteins and most hexoses other than glucose are
unable to enter the cerebrospinal fluid. It has been suggested that a barrier
similar to the blood-brain barrier exists in the choroid plexuses
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Electron-microscopic examination of a villus of a choroid plexusshows that the lumen of a blood capillary is separated from thelumen of the ventricle by the following structures:
1. the endothelial cells, which are fenestrated and have very thin walls (thefenestrations are not true perforations but are filled by a thin diaphragm);
2. a continuous basement membrane surrounding the capillary outside theendothelial cells;
3. scattered pale cells with flattened processes
4. a continuous basement membrane, on which rest
5. the choroidal epithelial cells
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The vertebral
artery
a branch of thefirst part of the
subclavian artery
ascends the neck
by passing
through theforamina in the
trasverse
processes of the
upper six cervical
vertebrae.
It enters the skull
through the
foramen magnum
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The basilar artery
formed by the union
of the two vertebral
arteries, ascends ina groove on the anterior
surface of the pons.
At the upper border
of the pons,
it divides intothe two posterior
cerebral arteries.
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The circle of Willis lies in the
interpeduncular fossa at thebase of the brain.
It is formed by the
anastomosis between the two
internal carotid arteries and
the two vertebral arteries .
The anterior communicating,
anterior cerebral, internal
carotid, posterior
communicating, posterior
cerebral, and basilar arteriesall contribute to the circle.
Circle of Willis
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The veins of the brain have no muscular tissuein their very thin walls, and they possess no
valves.
They emerge from the brain and lie in the
subarachnoid space.
They pierce the arachnoid mater and themeningeal layer of the dura and drain into the
cranial venous sinuses
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External Cerebral Veins
The superior cerebralveinsempty into thesuperior sagittal sinus
The superficial middlecerebral veinemptiesinto the cavernous sinus
The deep middle cerebralveindrains into thestraight sinus
Internal Cerebral Veins
empties into the straightsinus.
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The midbrainis drained
by veins that open into the
basal or great cerebral
veins.
The ponsis drained by
veins that open into the
basal vein, cerebellar
veins, or neighboring
venous sinuses.
The medulla oblongatais
drained by veins that open
into the spinal veins and
neighboring venous
sinuses.
The cerebellumis drained
by veins that empty into
the great cerebral vein or
adjacent venous sinuses.
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ARTERIAL SUPPLY OF CEREBRAL HEMISPHERES
Artery Origin Distribution
Internal Common carotid artery Gives branches to walls of cavernous
carotid at superior border of sinus, pituitary gland, and trigeminal
thyroid cartilage ganglion; provides primary supply to brain
Anterior Internal carotid artery Cerebral hemispheres, except for occipital
cerebral lobes
Anterior Anterior cerebral artery Cerebral arterial circle (of Willis)
communicating
Middle cerebral Continuation of internal Most of lateral surface of cerebral
carotid artery distal to hemispheres
anterior cerebral arteryVertebral Subclavian artery Cranial meninges and cerebellum
Basilar Formed by union of Brainstem, cerebellum, and cerebrum
vertebral arteries