White Matter (Medulla)

2. Cerebrum White Matter (Medulla) Dr. Zeenat Zaidi

3. White Matter • Underlies the cortex • Contains: • Nerve fibers (predominantly myelinated) • Neuroglia • Blood vessels • The nerve fibers originate, terminate or sometimes both, within the cortex

4. Depending on their origin & termination, these nerve fibers are classified into three types: • Association • B. Projection • C. Commissural

5. Association Fibers • Unite different parts of the same hemisphere • Are oftwo kinds: • Short association fibers: those connecting adjacent gyri, • Long association fibers:those connecting more distant gyri

6. Short Association Fibers • Lie immediately beneath the gray substance of the cortex • Connect together the adjacent gyri.

7. Long Association Fibers • Long fibers travel through white matter to connect distant areas of cerebral cortex • Link the primary sensory areasin parietal, temporal and occipital lobes to the association areas of the cerebral cortex, and to each other

8. Superior longitudinal fasciculus: connects the frontal, parietal, temporal and occipital lobes Uncinate fasciculus: connects frontal to temporal lobe, contributing to the regulation of behavior ArcuateFasciculus Broca’s Area Arcuate fasciculus: connect gyri in frontal to temporal lobes, important for language function Wernicke’s Area

9. Cingulum: connects frontal & parietal lobes to the para-hippocampalgyrus and adjacent temporal gyri Inferior longitudinal fasciculus: connects occipital to temporal pole & contributes to visual recognition

10. Commissural Fibers Corpus Callosum • Connect the corresponding regions of the two hemispheres • Include: • Corpus callosum • Anterior commissure • Hippocampalcommissure (commissure of fornix) *(Posterior commissure, not a cerebral commissure) F P

11. Corpus Callosum • Is a fibrous bridge located in the depth of the median longitudinal fissure • Connects the two cerebral hemispheres together • Shortercraniocaudally than is the hemisphere • Cranial end is nearer to the frontal pole of hemisphere as compared to caudal end to the occipital pole

12. C C The fibers in the corpus callosumconnect the corresponding regions of the two hemispheres with each other (except the inferior part of the temporal lobes)

13. Anterior forceps F C C P Posterior forceps O • 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)

14. Parts of Corpus Callosum Body Genu Splenium Rostrum

15. Anterior Commissure fornix IVF • Bundle of fibers runs transversely in front of the anterior columns of fornix • Connects the inferior and middle temporal gyri & theolfactory regions of the two hemispheres Anterior column of fornix

16. HippocampalCommissure • 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)

17. 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 P SC IC Cerebral aqueduct

18. Projection 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 awayfrom the cortex to the lower centers: (corticostriate, corticobulbar, corticopontine, corticospinal, & descending autonomic fibers)

19. corona radiata • 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

21. Internal Capsule BG • Bundle of projection fibers, passes through the interval between the thalamus and the basal ganglia Th

22. Has 5 parts: Anterior limb:between caudate (C) & lentiform(L) nuclei Genu Posterior limb:between thalamus(TH)& lentiform nucleus (L) Retrolenticular part: caudal to lentiform nucleus Sublenticular part: below lentiform nucleus(can not be seen in this section) C 1 2 L 3 Th 4

23. Anterior limbcontains: Thalamocortical projections that connect mediodorsal nucleus of thalamus with the prefrontal cortex Frontopontine fibers Genucontains: Corticobulbar fibers which connect the cortex with cranial nerve motor nuclei in the brainstem

24. Posterior limb contains: Corticospinal Corticobulbar Thalamocortical projections from: VPN to the primary somatosensory cortex VAN & VLN to motor regions of cortex

25. 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

26. 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

27. Clinical Notes Bilateral 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 intact Damage to corpus callosumleads to split-brain syndrome. The two half of the brain behave relatively autonomously Damage to splenium of corpus callosumleads to posterior disconnection syndrome of alexia (cannot understand written material) without agraphia(can speak and write without difficulty)

28. Thank You & Good Luck