White Matter

(Medulla)

Dr. Zeenat Zaidi

Cerebrum

White MatterWhite Matter• Underlies the

cortex• Contains:

•Nerve fibersNerve fibers (predominantly myelinated)

•NeurogliaNeuroglia•Blood Blood

vesselsvessels• The nerve fibers

originate, terminate or sometimes both, within the cortex

• Depending on their originorigin & terminationtermination, these nerve fibers are classified into three typesthree types:

A.A. AssociationAssociation

B. ProjectionProjection

C. Commissural

Association FibersAssociation Fibers• Unite different

parts of the same hemisphere

• Are of two kinds: • Short association Short association

fibersfibers: those connecting adjacent gyri,

• Long association Long association fibers:fibers: those connecting more distant gyri

Short Association FibersShort Association Fibers

• Lie immediately beneath the gray substance of the cortex

• Connect together the adjacent gyri.

Long Association FibersLong Association Fibers• Long fibers travel

through white matter to connect connect distant areasdistant areas of cerebral cortex

• Link the primary primary sensory areassensory areas in parietal, temporal and occipital lobes to the association areas association areas of the cerebral of the cerebral cortexcortex, and to to each othereach other

Superior Superior longitudinal longitudinal fasciculus: fasciculus: connects the frontal, parietal, temporal and occipital lobes

Uncinate Uncinate fasciculus: fasciculus: connects frontal to temporal lobe, contributing to the regulation of behavior

Arcuate Arcuate fasciculus: fasciculus: connect gyri in frontal to temporal lobes, important for language function

Wernicke’s Area

Broca’s Area

Arcuate Fasciculus

Cingulum: Cingulum: connects frontal & parietal lobes to the para-hippocampal gyrus and adjacent temporal gyriInferior Inferior longitudinal longitudinal fasciculus:fasciculus: connects occipital to temporal pole & contributes to visual recognition

Commissural FibersCommissural Fibers• Connect the

corresponding regions of the two hemispheres

• Include:• Corpus callosumCorpus callosum• Anterior commissureAnterior commissure• Hippocampal Hippocampal

commissure commissure (commissure of fornix)(commissure of fornix)

*(Posterior commissure, *(Posterior commissure, not a cerebral not a cerebral commissurecommissure))

Corpus Callosum

F

P

Corpus Corpus CallosumCallosum

• Is a fibrous bridge fibrous bridge located in the depth of the median longitudinal median longitudinal fissurefissure

• Connects the two cerebral hemispheres together

• ShorterShorter craniocaudally than is the hemisphere

• Cranial end is nearer to the frontal pole of hemisphere as compared to caudal end to the occipital pole

• The fibers in the corpus callosum corpus callosum connect the corresponding regions of the two hemispheres with each other (except the inferior part of the temporal lobes)

C

C

• Fibers linking the two frontal poles with each other, curve forward & form u-shaped anterior forceps (forceps minor)

• Fibers linking the two occipital poles with each other, curve backward & form u-shaped posterior forceps (forceps major)

F

P

O

C

C

Anterior forceps

Posterior forceps

Parts of Corpus Callosum

SpleniumSplenium

BodyGenu

Rostrum

Anterior Anterior CommissureCommissure

• Bundle of fibers runs transversely in front of the anterior columns of fornix

• Connects the inferior and middle temporal gyri & the olfactory regions of the two hemispheres

Anterior column of fornix

fornix

IVF

Hippocampal CommissureHippocampal Commissure• Bundle of fibers

runs transversely between the crura of the fornix

• Connect the two hippocampi with each other

• (note that hippocampo-mamillary fibers do not cross)

Posterior Commissure• Rounded band of

white fibers• Crossing the midline

on the dorsal aspect of the upper end of the cerebral aqueduct (located between superior colliculus & pineal body)

• Connects the left and right midbrain. Plays important role in the bilateral pupillary reflex

SC

P

IC

Cerebral aqueduct

Projection FibersProjection Fibers• Fibers running vertically

through the hemispheres• Consist of:

• Cortical afferent fibers conveying impulses to the cerebral cortex: (mainly thalamo-cortical fibers)

• Cortical efferent fibers carrying impulses away from the cortex to the lower centers: (corticostriate, corticobulbar, corticopontine, corticospinal, & descending autonomic fibers)

• Deeper to the cortex, these fibers are arranged radially as the corona radiata

• Then the fibers converge to form a sheath, called the internal capsule, that passes between the thalamus and the basal ganglia

• Continue in the:• Crus of the midbrain• Basilar part of pons• Pyramid of medulla

oblongata• Continue in the spinal

cord as the corticospinal tracts

corona radiata

Internal Internal CapsuleCapsule

• Bundle of projection fibers, passes through the interval between the thalamus and the basal ganglia

BG

Th

Has 5 parts5 parts:• Anterior limb: between

caudate (C) & lentiform (LL) nuclei

• Genu• Posterior limb: between

thalamus (THTH) & lentiform nucleus (LL)

• Retrolenticular part: caudal to lentiform nucleus

• Sublenticular part: below lentiform nucleus (can not be seen in this section)

C

Th

L

• Anterior limbAnterior limb contains:

• Thalamocortical projections that connect mediodorsal nucleus of thalamus with the prefrontal cortex

• Frontopontine fibers

• GenuGenu contains:

• Corticobulbar fibers which connect the cortex with cranial nerve motor nuclei in the brainstem

• Posterior limb Posterior limb contains:• Corticospinal• Corticobulbar• Thalamocortical

projections from:•VPN to the

primary somatosensory cortex

•VAN & VLN to motor regions of cortex

• Retrolenticular part contains thalamocortical projections:

• Geniculocalcarine fibers (visual radiation), from the lateral geniculate nucleus of thalamus to the visual cortex in the occipital lobe

• & few Geniculotemporal fibers (auditory radiation) from the medial geniculate nucleus of thalamus to the auditory cortex in the temporal lobe

• Sublenticular part Sublenticular part contains thalamocortical projections: geniculo-temporal fibers (auditory radiation) from the medial geniculate nucleus of thalamus to the auditory cortex in the temporal lobe

Clinical NotesClinical NotesBilateral lesion of the inferior longitudinal Bilateral lesion of the inferior longitudinal

fasciculus fasciculus (as in carbon monoxide poisoning)(as in carbon monoxide poisoning), , leads to:leads to:

• Loss of identification of the:Loss of identification of the:• Nature of objects (Nature of objects (object agnosiaobject agnosia))• Individual faces (Individual faces (prosopagnosiaprosopagnosia))

• The elementary vision remains intactThe elementary vision remains intactDamage to corpus callosum Damage to corpus callosum leads to leads to split-brain split-brain

syndromesyndrome. The two half of the brain behave . The two half of the brain behave relatively autonomouslyrelatively autonomously

Damage to splenium of corpus callosum Damage to splenium of corpus callosum leads leads to to posterior disconnection syndrome posterior disconnection syndrome of of alexiaalexia (cannot understand written material) (cannot understand written material) without without agraphia agraphia (can speak and write without (can speak and write without difficulty)difficulty)

Lateral Ventricle

Lateral VentricleLateral Ventricle• The 2 lateral

ventricles are the largest of the ventricles.

• Each lateral ventricle is:• A C-shaped cavity

located within cerebral hemisphere

• Communicates with the 3rd ventricle through the interventricular foramen

• Each lateral ventricle consists of:• An Anterior

horn• A Central part,

the Body• A Posterior

(occipital) horn • An Inferior

(temporal) horn

Anterior Anterior HornHorn

• Lies anterior to the interventricular foramen.

• Roof and anterior Roof and anterior wallwall: formed by the corpus callosum

• Medial wallMedial wall: formed by the septum pellucidum.

• Floor & lateral wallFloor & lateral wall: formed by the head of the caudate nucleus.

Septum pellucidum

Central Part Central Part (Body)(Body)

• Extends from the interventricular foramen to the splenium of the corpus callosum

• RoofRoof: formed by the corpus callosum

• Medial wallMedial wall: formed by the posterior part of the septum pellucidum

• FloorFloor: formed by (from lateral to medial) caudate nucleus, thalamus, choroid plexus and fornix.

CC

ThCPF

C

E

Posterior HornPosterior Horn• Extends into the

occipital lobe.• RoofRoof: formed by fibers

of the corpus callosum.• Medial wallMedial wall shows two

ridges: • Upper called the bulb of

posterior horn is produced by fibers of forceps major &

• Lower called calcar avis, produced by the calcarine sulcus

Inferior Inferior HornHorn• Extends into the

temporal lobe.• RoofRoof: formed by the:

• white substance of the cerebral hemisphere

• stria terminalis• tail of the caudate

nucleus.• The amygdaloid nucleus

(A) bulges into the terminal part of the inferior horn

• FloorFloor and the medial wallmedial wall are formed by (from medial to lateral) the fimbria, the hippocampus and the collateral eminence.

Caudate nucleus

Hippocampus

Inferior horn of LV

Choroid Choroid PlexusPlexus

• Projects into the ventricular cavity from its medial aspect

• Found in the central part and the inferior horn, but not in the anterior or posterior horns

• Continues with the choroid plexus of 3rd ventricle through the interventricular foramen.

Septum Septum PellucidumPellucidum• Paired membranes

• Each lies on each side of the midline

• Fill the gap between the corpus callosum and the fornix

• Form the medial wall of the lateral ventricle (body & anterior horn)

• The two membranes are separated from each other by a midline slit like closed cavity, the cavum septum pellucidum, which has no communication with the ventricular system of the brain

F

CC

Cavum Cavum septum septum pellucidumpellucidum

T

CCLV

III Ventricle

FOOD FOR THOUGHT• A right handed person had severe epileptic attacks, for which

his corpus callosum was severed in the midline. If the following tests are performed on this patient, What do you expect to get in the results and why?

• Ask the patients to close the eyes

1. Give him a small soft rubber ball to hold in his left hand and ask him to identify this structure, its shape, size & texture etc etc.

2. Now repeat the same while he holds the ball in his right hand.

3. Now ask the patient to open the eyes. Move the ball first into his left visual field

4. and then into his right visual field and ask the same questions

Thank You & Good Luck