White Matter (Medulla) Dr. Zeenat Zaidi Cerebrum

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  • White Matter (Medulla)Dr. Zeenat ZaidiCerebrum

  • White MatterUnderlies the cortexContains:Nerve fibers (predominantly myelinated)NeurogliaBlood vesselsThe nerve fibers originate, terminate or sometimes both, within the cortex

  • Depending on their origin & termination, these nerve fibers are classified into three types:Association

    B. Projection

    C. Commissural

  • Association FibersUnite different parts of the same hemisphereAre of two kinds: Short association fibers: those connecting adjacent gyri, Long association fibers: those connecting more distant gyri

  • Short Association FibersLie immediately beneath the gray substance of the cortexConnect together the adjacent gyri.

  • Long Association FibersLong fibers travel through white matter to connect distant areas of cerebral cortexLink the primary sensory areas in parietal, temporal and occipital lobes to the association areas of the cerebral cortex, and to each other

  • Superior longitudinal fasciculus: connects the frontal, parietal, temporal and occipital lobesUncinate fasciculus: connects frontal to temporal lobe, contributing to the regulation of behaviorArcuate fasciculus: connect gyri in frontal to temporal lobes, important for language function Wernickes AreaBrocas AreaArcuate Fasciculus

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

  • Commissural FibersConnect the corresponding regions of the two hemispheresInclude:Corpus callosumAnterior commissureHippocampal commissure (commissure of fornix)*(Posterior commissure, not a cerebral commissure)

    Corpus CallosumFP

  • Corpus CallosumIs a fibrous bridge located in the depth of the median longitudinal fissureConnects the two cerebral hemispheres togetherShorter craniocaudally than is the hemisphereCranial end is nearer to the frontal pole of hemisphere as compared to caudal end to the occipital pole

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



  • 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)


    CAnterior forcepsPosterior forceps

  • Parts of Corpus CallosumSpleniumBodyGenuRostrum

  • Anterior CommissureBundle of fibers runs transversely in front of the anterior columns of fornixConnects the inferior and middle temporal gyri & the olfactory regions of the two hemispheresAnterior column of fornixfornixIVF

  • Hippocampal CommissureBundle of fibers runs transversely between the crura of the fornixConnect the two hippocampi with each other (note that hippocampo-mamillary fibers do not cross)

  • Posterior Commissure

    Rounded band of white fibersCrossing 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 reflexSCPICCerebral aqueduct

  • Projection FibersFibers running vertically through the hemispheresConsist 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 radiataThen the fibers converge to form a sheath, called the internal capsule, that passes between the thalamus and the basal gangliaContinue in the:Crus of the midbrainBasilar part of ponsPyramid of medulla oblongataContinue in the spinal cord as the corticospinal tracts

    corona radiata

  • Internal CapsuleBundle of projection fibers, passes through the interval between the thalamus and the basal gangliaBGTh

  • Has 5 parts:Anterior limb: between caudate (C) & lentiform (L) nucleiGenuPosterior limb: between thalamus (TH) & lentiform nucleus (L)Retrolenticular part: caudal to lentiform nucleusSublenticular part: below lentiform nucleus (can not be seen in this section)


  • Anterior limb contains:Thalamocortical projections that connect mediodorsal nucleus of thalamus with the prefrontal cortex Frontopontine fibersGenu contains:Corticobulbar fibers which connect the cortex with cranial nerve motor nuclei in the brainstem

  • Posterior limb contains:CorticospinalCorticobulbarThalamocortical projections from:VPN to the primary somatosensory cortexVAN & 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 contains thalamocortical projections: geniculo-temporal fibers (auditory radiation) from the medial geniculate nucleus of thalamus to the auditory cortex in the temporal lobe

  • Clinical NotesBilateral lesion of the inferior longitudinal fasciculus (as in carbon monoxide poisoning), leads to:Loss of identification of the:Nature of objects (object agnosia)Individual faces (prosopagnosia)The elementary vision remains intactDamage to corpus callosum leads to split-brain syndrome. The two half of the brain behave relatively autonomouslyDamage to splenium of corpus callosum leads to posterior disconnection syndrome of alexia (cannot understand written material) without agraphia (can speak and write without difficulty)

  • Lateral Ventricle

  • Lateral VentricleThe 2 lateral ventricles are the largest of the ventricles. Each lateral ventricle is:A C-shaped cavity located within cerebral hemisphereCommunicates with the 3rd ventricle through the interventricular foramen

  • Each lateral ventricle consists of:An Anterior hornA Central part, the BodyA Posterior (occipital) horn An Inferior (temporal) horn

  • Anterior HornLies anterior to the interventricular foramen.Roof and anterior wall: formed by the corpus callosumMedial wall: formed by the septum pellucidum. Floor & lateral wall: formed by the head of the caudate nucleus.

  • Septum pellucidumCentral Part (Body)Extends from the interventricular foramen to the splenium of the corpus callosumRoof: formed by the corpus callosumMedial wall: formed by the posterior part of the septum pellucidumFloor: formed by (from lateral to medial) caudate nucleus, thalamus, choroid plexus and fornix. CCThCPFCE

  • Posterior HornExtends into the occipital lobe.Roof: formed by fibers of the corpus callosum.Medial 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 HornExtends into the temporal lobe.Roof: formed by the:white substance of the cerebral hemispherestria terminalistail of the caudate nucleus.The amygdaloid nucleus (A) bulges into the terminal part of the inferior hornFloor and the medial wall are formed by (from medial to lateral) the fimbria, the hippocampus and the collateral eminence.Caudate nucleusHippocampusInferior horn of LV

  • Choroid PlexusProjects into the ventricular cavity from its medial aspectFound in the central part and the inferior horn, but not in the anterior or posterior hornsContinues with the choroid plexus of 3rd ventricle through the interventricular foramen.

  • Septum PellucidumPaired membranesEach lies on each side of the midlineFill the gap between the corpus callosum and the fornixForm 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

    FCCCavum septum pellucidumTCCLVIII Ventricle

  • FOOD FOR THOUGHTA 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 eyesGive 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.Now repeat the same while he holds the ball in his right hand.Now ask the patient to open the eyes. Move the ball first into his left visual field and then into his right visual field and ask the same questions

  • Thank You & Good Luck