1. Internal Structure of the Cerebral Hemisphere
By Dr. Samah Alsaid

2. Each cerebral hemisphere consists of :
Gray matter (cerebral cortex) on the surface.
White matter forming the core.
Basal ganglia(collection of gray matter embedded in the white matter core near the base of the brain).
Lateral ventricle(cavity).

4. Lateral ventricles
Two lateral ventricles – one is in each cerebral hemisphere
It communicates with the third ventricle through interventricular foramen
C – shaped
Body – lies in the parietal lobe
Anterior horn – frontal lobe
Posterior horn – occipital lobe
Inferior horn – temporal lobe

6. Basal Ganglia
Definition: The basal nuclei(ganglia) are collections of gray matter(nerve cells) which are deeply placed inside the white matter of the cerebral hemisphere, near the base of the brain. Components: a-The caudate nucleus. b-The lentiform nucleus. C-The amygdaloid nucleus………(a small centre) d-The claustrum………………………( unknown function)

7. Basal nuclei
Corpus striatum
Amygdaloid
nucleus
Claustrum

8. Brain: Basal ganglia

9. White matter Composed of mylinated nerve fibers
Classified into three groups:
Commissural fibers
Association fibers
Projection fibers

10. Commissural fibres
A commissure: Is a band of white matter ( nerve fibres) connecting a part of the CNS-one hemisphere- on one side with the same part of the opposite side, So help to co-ordinate the activities of both hemispheres.
There are three major commissures:
a- The corpus callosum.
b-The anterior commissure.
c- The hippocampal commissure.

11. Commissural fibers Connect corresponding regions of two hemispheres
They are:
Corpus callosum
Anterior commissure
Posterior commissure
Fornix
Habenular commissure

12. Corpus callosum Largest commissure Parts: Rostrum Genu Body Splenium

13. Association fibers
Connect various cortical regions within the same hemisphere
They are:
Short association fibers - connect adjacent gyri
Long association fibers – collected into named bundles. They are:
Uncinate fascicullus
Cingulum
Superior longitudinal fascicullus
Inferior longitudinal fascicullus
Fronto-occipital fascicullus

14. Association fibers

15. Projection fibers
They are the fibres which pass through the internal capsule either :
A- To the cortex( from the thalamus); afferents.
B- Or from the cortex to the lower centres; efferents.

16. A- Projection fibres to the cerebral cortex(from thalamus):
All impulses to the cerebral cortex must stop first in the thalamus; so the only fibres which reach the cortex come from the thalamus and are called thalamo-cortical fibres or the thalamic radiation.
The thalamo-corical projections(radiation) of clinical importanc are:
Sensory radiation((superior thalamic radiation)
Visual (optic) radiation
Auditory radiation

17. Projection fibres from the cerebral cortex to the lower centres
The pyramidal tract(cortico-spinal and corticobulbar fibres)
Cortico-pontine fibres:
Fronto-pontine fibres.
Temporo-parieto-occipito-pontine fibres.
iii- Many extrapyramidal fibres to many extra-pyramidal centers.
iv. Cortico-thalamic fibres to different nuclei of the thalamus

18. Projection fibers

19. Internal capsule
The internal capsule is an area of white matter in the brain that separates the caudate nucleus and the thalamus from the lenticular nucleus. The internal capsule contains both ascending and descending axons.
It consists of axonal fibres that run between the cerebral cortex and the pyramids of the medulla.

20. Components The internal capsule is V-shaped when.
When cut horizontally:
the bend in the V is called the genu
the anterior limb : is the part in front of the genu between the head of the caudate nucleus and the lenticular nucleus

21. the posterior limb is the part behind the genu, between the thalamus and lenticular nucleus.
the retrolenticular portion is caudal to the lenticular nucleus and carries optic tracts including the geniculocalcarine radiations.
the sublenticular portion is beneath the lenticular nucleus and are tracts involved in the auditory pathway from medial geniculate nucleus to the primary auditory cortex (Brodmann Area 41)

22. Brain: Internal capsule

23. Fibers
The posterior limb of the internal capsule contains corticospinal fibers, sensory fibers (including the medial lemniscus and the anterolateral system) from the body and a few corticobulbar fibers.
The genu contains corticobulbar fibers, which run between the cortex and the brainstem.
The anterior limb of the internal capsule contains:
1) frontopontine (corticofugal) fibers project from frontal cortex to pons;
2) thalamocortical fibers connect the medial and anterior nuclei of the thalamus to the frontal lobes (these are severed during a prefrontal lobotomy).

24. c-The retrolenticular part contains fibers from the optic system, coming from the lateral geniculate nucleus of the thalamus. More posteriorly, this becomes the optic radiation. Some fibers from the medial geniculate nucleus (which carry auditory information) also pass in the retrolenticular internal capsule, but most are in the sublenticular part. d-The sublenticular part contains fibers connecting the with the

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