BYPROF.SAEED ABUEL MAKAREM

WHIT MATTER OF

THE CERBRUM

White matter of Cerebrum• Each cerebral hemisphere

consists of:• 1- Cerebral cortex: (outer layer of grey matter).• 2- White matter: (enormous mass of nerve

fibers).• 3- Basal ganglia: (collection of grey matter in

the white matter).• 4- Lateral ventricle: The cavity of the hemisphere.

WHITE MATTER OF CEREBRAL HEMISPHERE

• There are 3 types:• 1- Association fibers:• Interconnect cortical sites

lying within one hemisphere.• They are short or long fibers .• 2- Commissural fibers:• Connecting functionally

related gyri on both hemisphere.

• 3- Projection fibers:• Connecting the cortex with

the lower centers in thalamus brain stem, or spinal cord.

• They are ascending or descending.

• A- Short association fibers:

• Connect nearer gyri on the same hemisphere.

• B- Long association fibers:

• Connect distant gyri on the same hemisphere.

• Example:• 1-Superior

longitudinal fasciculus:

Association fibers

Association fibersExample:1-Superior longitudinal fasciculus:Connects the frontal & occipital lobes.It lies above the insula.It has a subsidiary bundle known as arcuate fasciculus, which connects the frontal & temporal lobes.It is important for language function

Association fibers• 2- Inferior longitudinal fasciculus:

• Connects the occipital & temporal poles.

• It is contributed in visual recognition.

• 3- Uncinate fasciculus:• U-shaped curved around

the bottom of the lateral sulcus.

• It connects the anterior & inferior parts of the frontal gyrus with the temporal gyri.

• It is important for behavioral regulation.

Association fibers• 4- Cingulum:• Begins in the anterior

perforated substance in the frontal lobe.

• Runs in cingulate gyrus.• Curves inferiorly to run

in the Parahippocampal gyrus.

• It is a part of the limbic system

• It terminates in the Uncus, (smell center).

COMMISSURAL FIBERS

• The major commissural fibers are:

• 1-Corps callosum.• 2-Anterior commissure. • 3-Hippocampal

commissure ( Commissure of the fornix).

CORPUS CALLOSUM• The greatest commissure

of brain.• It connects homologous

areas of the 2 cereral hemispheres

• Formed of 4 parts: Rostrum, genu, body & splenium.

• Lies in floor of great longitudinal fissure .

• Its inferior surface is attached to fornix by the septum pellucidum.

CORPUS CALLOSUM• Rostrum & genu interconnect the anterior part of the frontal lobe.

• The trunk interconnects the posterior part of the frontal & parietal & temporal lobes.

• The splenium interconnects the occipital lobes.

• The fibers of the rostrum & genu arch forward to form forceps minor.

• The fibers of splenium arch backward to form forceps major.

ANTERIOR COMISSURE

• Rounded commissure.• Lies behind the lamina

terminals.• Runs transversely in

front of the anterior column of fornix.

• Interconnects the middle & inferior temporal gyri.

• Also, it connects the olfactory regions of the 2 hemisphere.

HIPPOCAMPAL COMMISSURE

• Composed of transverse fibers .• Interconnects the posterior columns of the fornix.

PROJECTION FIBERS• These are fibers which connect the cortex to other areas in the brain stem & the spinal cord.

• Projection fibers are 2 types:

• A- Ascending (afferent),or corticopetal:

• Conveying fibers to the cortex

• 1- Thalamic radiation: connecting different thalamic nuclei with different parts of cortex.

• 2- Optic radiation.• 3- Auditory radiation.

PROJECTION FIBERS• B- Descending (Efferent), or

corticofugal:

• 1. Pyramidal: a. Corticospinal. b. Corticobulbar.

• 2. Corticopontine.

• 3. Corticoreticular.

• 4. Corticorubral

INTERNAL CAPSULE• Thick band of projection fibers, (porta cerebri).

• V-shaped with its concavity directed laterally in horizontal section

• Its concavity is related to Lentiform nucleus.

• It is formed of:• Anterior limb.• Genu.• Posterior limb.

INTERNAL CAPSULE• Anterior limb:• Between head of caudate

nucleus & lentiform nucleus.

• It contains:• 1-Anterior thalamic

radiation: From anterior & mediodorsal

thalamic nuclei, to the frontal cortex.

• 2-Frontopontine fibers: That project to pontine nuclei, in the basal part of the Pons.

INTERNAL CAPSULE• Genu of internal capsule:• Is the angle of the V which

points medially, between head of caudate nucleus and thalamus.

• It contains:• 1- Corticonuclear (Corticobulbar).• 2- Anterior part of sensory

(superior thalamic) radiation, from ventral anterior & ventral lateral nuclei to motor regions of the frontal lobe.

INTERNAL CAPSULE• Posterior limb:• A-Lenticothalamic part• Lies between thalamus &

lentiform nucleus.• Contains:• 1-Corticospinal fibers.• 2-Frontopontine.• 3-Frontorubral.• 4-Great part of sensory

(superior thalamic ) radiation, from the ventral posterior nucleus to the primary somatosensory cortex.

INTERNAL CAPSULE• B-Retrolentiular part:

• It contains fibers from medial & lateral geniculate nuclei of thalamus, which form the auditory & optic radiation.

• Optic radiation passes to visual cortex, around the calcarine sulcus (geniculoalcarine fibers).

• Auditory radiation passes to superior temporal gyrus.