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CORPUS CALLOSUM
The corpus callosum is a large bundle of axons that connects the right and left cerebral hemispheres. The axons are processes of pyramidal cells in the cerebral cortex, and they carry information, in the form of patterns of nerve impulses, from cells of one hemisphere to cells in the contralateral hemisphere. The cell bodies of the axons in the corpus callosum are found mostly in the second and third layers (the Outer Granular Layer and the Outer Pyramidal Layer, respectively) of the cerebral cortex. Coordinated activity of the two hemispheres, and the unity of the brain itself, depend on the adequate functioning of the axons in the corpus callosum.
Connections between the right and left halves of the brain are called Commissural Connections. The corpus callosum is the largest of the commissural connecting bundles. The axons in the corpus callosum are coated with myelin, a fatty substance that covers large axons and speeds up conduction of the impulses. This gives the corpus callosum a white appearance in unstained sections, and in the cell-stained sections in this atlas. It forms part of the "white matter" of the brain. In the fiber-stained sections in this atlas, myelin is stained a blue-black color, so the corpus callosum appears black. About one-third of the information traveling to a cerebral hemisphere comes from the corpus callosum (that is to say, it comes from the contralateral hemisphere). Correspondingly, about one-third of the information sent by the cortex of one hemisphere is destined for the other hemisphere, through the corpus callosum. The lower parts of each hemisphere send some, most , or all of their commissural fibers through the Anterior Commissure rather than through the corpus callosum. |
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