• Fibres of white matter connect the various parts of the central nervous system.
• They are classified into following three types, on the basis of the types of connections they provide.
1. Association fibres.
2. Commissural fibres.
3. Projection fibres.
ASSOCIATION (ARCUATE) FIBRES
Short Association Fibres
•These fibres connect adjacent gyri to one another.
Long Association Fibres
•These fibres connect more widely separated gyri to one another.
1. The uncinate fasciculus, 2. The cingulum,
3. The superior longitudinal fasciculus 4. The inferior longitudinal fasciculus 5. Fronto-occipital fasciculus
Association fibres of cerebrum
•These are fibres which connect the cerebral cortex to other parts of the CNS, e.g. the brain stem and spinal cord.
Examples: (a) Corona radiata and (b) internal capsule.
Fibres of various parts of internal capsule
•These are the fibres which connect corresponding parts of the two hemispheres.
1. The corpus callosum
2. The anterior commissure, 3. The posterior commissure, 4. The commissure of the fornix 5. The habenular commissure 6. The hypothalamic commissures
• corpus callosum is the largest commissure of the brain
• It connects the two cerebral hemispheres.
• It forms a massive arched interhemispheric bridge in the floor of the median longitudinal cerebral fissure connecting the medial surfaces of the two cerebral hemispheres.
• In sagittal section of cerebrum it is seen as C-shaped mass of white fibres on the medial surface of the hemisphere forming the roof of the lateral ventricle.
Parts of corpus callosum
Some of the relations of corpus callosum in the coronal section of the brain passing through the central parts of lateral ventricles parts.
Parts of Corpus Callosum
1. The genu 2. The rostrum 3. The trunk 4.The splenium
• It is thick curved anterior extremity of corpus callosum which lies 4 cm behind the frontal pole.
•The fibres of genu curve forwards on either side into the anterior parts of the frontal lobes, forming a fork-like structure, the forceps minor.
•The genu extends downwards and backwards as a thin prolongation to join the lamina terminalis forming, rostrum of corpus callosum.
•The trunk is main (middle) part of the corpus callosum.
•Its fibres connect most of the frontal and anterior parts of the parietal lobes of the two cerebral hemispheres.
•The splenium is the massive posterior extremity of the corpus callosum.
•The fibres of the splenium connect the posterior parts of the parietal lobes, and temporal and occipital lobes of the two hemispheres.
•The fibres connecting the occipital lobes sweep backwards on either side above the calcarine sulcus forming a large fork-like structure, the forceps major (Fig. 14.5).
•The tapetum is the thin lamina of white fibres which forms the roof and lateral wall of the posterior horn; and lateral wall of the inferior horn of the lateral ventricle.
•The tapetum is formed by those fibres of the trunk and splenium of corpus callosum which are not intersected by the fibres of corona radiata.
•In the coronal section, the tapetum looks whiter than the surrounding white matter because section passes parallel to the fibres of the
Fibres of corpus collosum
•The corpus callosum helps in coordinating activities of the two hemispheres.
•Responsible for interhemispheric transfer of information which is essential for bilateral responses and in learning processes.