Overview CNS - Drg. Yuni

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

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Overview CNS - Drg. Yuni

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