ـطي The basal ganglia (nuclei)



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Neuro Anatomy

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The basal ganglia (nuclei): -

Is a collection of small masses of gray matter situated within the white matter (medulla) of each cerebral hemisphere as dispersed masses, the internal capsule passes between these nuclei & separated them from each other. They include: -



  1. Corpus striatum.

  2. The amygdaloid nucleus.

  3. The claustrum.

The corpus striatum is situated lateral to the thalamus, it is completely divided by the internal capsule into: -

  1. The caudate nucleus.

  2. The Lentiform nucleus.



  1. The caudate is coma shaped mass which is closely related to the lateral ventricle & lies lateral to the thalamus. It has the following parts: - head, body & tail.

  • The head lies in the floor of the anterior horn & being separated from the lentiform nucleus by the anterior limb of the internal capsule. It is supplied by striate branches of the middle & anterior cerebral arteries.

  • The body runs in the floor of the central part of the lateral ventricle.

  • Tail is long & narrow part, it curves behind the thalamus to run in the roof of the inferior horn. It terminates by fusing with the amygdaloid nucleus just above the tip of the inferior horn.



  1. The lentiform nucleus is a relatively large lens-like mass & lies lateral to the thalamus & separated from it by the posterior limb of the internal capsule. It has 3 surfaces; lateral, medial & inferior.

The lateral surface is separated from the claustrum by the external capsule. The medial surface is convex & being separated from both head of caudate & thalamus by the anterior & posterior limbs of the internal capsule respectively. The inferior surface lies over the fibers of the auditory radiation.

The lentiform nucleus is subdivided into 2 parts: -

  1. Putamen is the dark lateral part of the lentiform nucleus.

  2. Globus pallidus is the pale medial part of the lentiform nucleus.

The caudate & putamen receive afferents from: -

  1. Cerebral cortex (mainly from pre-motor area).

  2. Thalamus (mainly medial nucleus).

While the Globus pallidus gives efferent to: -

  1. Thalamus.

  2. Hypothalamus.

  3. Sub thalamus.

  4. Tegmentum of mid brain.

  5. Reticular formation of the brain stem.

Claustrum: -thin plate of gray matter lies lateral to lentiform where it is separated from it by external capsule. It also separated from the cortex of insula by the sub-cortical white matter of the insula.

Amygdaloid: -located over the tip of inferior horn, it is fused with the tail of caudate, uncus&stria terminals. It receives afferent from the olfactory system & sends efferent to stria terminals.

The Cerebrospinal Fluid

Is the fluid present in the ventricles of the brain and in the subarachnoid spaces around the brain and spinal cord.The C.S.F of the ventricular system is completely separated from that present in the subarachnoid spaces.The only place where the C.S.F of ventricular & subarachnoid spaces are mixed together is in the Dural sac (Terminal or 5th ventricle) below the lower end of the spinal cord.

Production of C.S.F is

1-Mainly by active secretion from the choroid plexus of the ventricles.

2-Some may originate as tissue fluids formed in the brain substance .



Drainage:

1-Via arachnoid granulation &Velli to the venous sinuses.

2-Some of it is absorbed directly by the veins present in the subarachnoid spaces.

3-Some of is drained to out side by perineural lymphatic vessels.



Circulation

That secreted by the choroid plexus of the lateral ventricle will pass via foramen of Monro to the 3rd ventricle where the choroid plexus of this ventricle add some fluid to it from its choroid plexus,then it pass via cerebral aquidut of Mid brain to reach the 4th ventricle and the choroid plexus of this ventricle will add to it some amount produced here then the C.S.F will pas in either direction as :

A-Some will leave to the central canal of the spinal cord via the opening at the lower half of the Medulla Oblongata to reach eventually the Dural Sac.

B-The other will escape to the subarachnoid spaces via median aperture(of Magendi) and the 2 lateral apertures of Luschka to reach the Cisterna magna and Cisterna pontis respectively and from here will circulate in the subarachnoid spaces around the brain and spinal cord which eventually reach the Dural Sac.

It is produced at a rate of 0.5 ml per minute and total volume of the C.S.F is around 140 ml which can be replaced completely within 4-5 hours.

If the fluid is too much results in Hydrocephalus which could be due to :

1-Excessive production as in cases of tumours of the choroid plexus of the ventricles.

2-Delayed drainage due to blochage at some foramena in the roof of the 4th ventricle or along its course of drainage as by tumour compressing foramen of Monro or the cerebral aqueduct.



Blood brain barrier

Is present between the blood vessels and the extracellular spaces of the brain it is formed by:

1-Endothelial cells in the blood capillaries.

2-Continuos basement membrane surrounding blood capillaries.



3-Foot processes of Astrocytes.




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