White Matter Explained PDF

Medullary Substance (White Matter)  Projection fibers interconnect cortex with lower centers in thalamus, brainstem and spinal cord  Association fibers interconnect various cortical regions of the same hemisphere  Commisural fibers interconnect coresponding cortical regions of...

Medullary Substance (White Matter)  Projection fibers interconnect cortex with lower centers in thalamus, brainstem and spinal cord  Association fibers interconnect various cortical regions of the same hemisphere  Commisural fibers interconnect coresponding cortical regions of the two hemispheres  Projection fibers corona radiata Commissural fibers Corpus callosum rostrum, genu, trunk, splenium Anterior commissure Commissure of fornix Association fibers Short association fiber Long association fiber Fibers of Cerebral White Matter  1. Corpus callosum CH3-PI24  2. Internal capsule  4. Superior longitudinal  fasciculus  6. Cingulum  7. Uncinate fasciculus  8. Inferior longitudinal  fasciculus  These are fibers which connect the cortex to other areas in the brain stem PROJECTION FIBERS & the spinal cord. Projection fibers are 2 types: A- Ascending (afferent): 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): 1. Pyramidal: a. Corticospinal b. Corticobulbar 2. Corticopontine 3. Corticoreticular 4. Corticorubral Thick band of projection fibers. INTERNAL CAPSULE V-shaped with its concavity directed laterally in horizontal section Its concavity is related to Lentiform nucleus. It is formed of: Anterior limb; between caudate nucleus and lentiform nucleus Posterior limb; between thalamus and lentiform nucleus Genu; the region between anterior and posterior limbs of internal capsule  Anterior limb: INTERNAL CAPSULE Between head of caudate nucleus & lentiform nucleus. It contains: 1-Anterior thalamic radiation: From thalamic nuclei to the frontal cortex 2-Frontopontine fibers: That project to pontine nuclei  Genu of internal capsule: 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.  Posterior limb: INTERNAL CAPSULE A-Thalamolentiform part: 1-Corticospinal 2-Corticorubral 3-Central thalamic radiation (thalamoparietal fibers) 4-Corticothalamic fibers B-Retrolentiform part: INTERNAL CAPSULE Posterior thalamic radiation; fibers connecting caudal part of thalamus to parietal and occipital lobes. It contains fibers from lateral geniculate nuclei of thalamus, which form optic radiation. Optic radiation passes to visual cortex, around the calcarine sulcus (geniculoalcarine fibers).  C-Sublentiform part INTERNAL CAPSULE Lies between thalamus & lentiform nucleus. Contains: 1-Corticospinal fibers 2-Parietopontine & Temporopontine 3-Corticotectal fibers 4-Great part of sensory (superior thalamic ) radiation, from the ventral posterior nucleus to the primary somatosensory cortex. Auditory radiation passes to superior temporal gyrus. 1. anterior thalamic radiation 2. central sulcus 3. precentral gyrus 4. central thalamic radiation 5.optic radiation 6. auditory radiation 7.internal capsule 8. corticostriate fiber 9. corticothalamic fiber 10. corticopontine fiber 11. pontocerebellar fiber 12. corticobulbar tract 13.corticospinal tract) 14. corticofugal fibers Association Fibers 1)Short asociation fibers; adjacent gyri 2)Long Association Fibers a) Superior longitudinal fasciculus connects the anterior part of the frontal lobe to the occipital and temporal lobes b) Inferior longitudinal fasciculus connects the occipital and temporal lobes c) Uncinate fasciculus around the anterior of lateral sulcus conncets the anterior parts of frontal and temporal lobes. d) Cingulum; located in the gyrus cinguli, frontal and parietal lobes with parahippocampal and adjacent temporal cortical regions. e) Fronto-occipital fibers connect frontal lobe to occipital lobe and temporal lobes f) Ventral occipital fibers connect parietal and occipital lobes to temporal lobe.  A- Short association fibers: Connect nearer gyri on the same Association fibers hemisphere. B- Long association fibers: Connect distant gyri on the same hemisphere. Example: 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 Superior longitudinal fasciculus (arcuate fascicuslus)  2- Inferior longitudinal fasciculus: Connects the occipital & temporal Association fibers 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.  4- Cingulum: Association fibers 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. cingulum, uncinate fasciculus Inferior longitudinal fasciculus superior longitudinal fasciculus  Commisural Fibers Corpus Callosum Anterior Commisure Posterior Commisure Commisure of hippocampus (fornix) Habenular Commisure  COMMISSURAL FIBERS The major commissural fibers are: 1-Corpus 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 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; thin anterior part, prolonged posteriorly and inferiorly with lamina terminalis Genu; the curved anterior end of the corpus callosum, found in front of the septum pellicidum Body; between genu and splenium Splenium; posterior thick part Rostrum & genu interconnect the CORPUS CALLOSUM 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.