Medical brain notes 24

  The Internal Capsule       A preliminary description of the internal capsule is given. This should be read before studying the details of the fibres passing through the capsule.         The fibres passing through the capsule may be ascending (to the cerebral cortex) or descending (from the cortex). The arrangement of fibres is easily remembered if it is realized that any group of fibres within the capsule  takes the most direct path  to its destination. Thus fibres to and from the anterior part of the frontal lobe pass through the anterior limb of the internal capsule. Those to and from the posterior part of the frontal lobe, and from the greater part of the parietal lobe, occupy the genu and posterior limb of the capsule. Fibres to and from the temporal lobe occupy the sublentiform part (Fig. 17.3), while those to and from the occipital lobe pass through the retrolentiform part. Some fibres from the lowest par...

  Commissures of the Brain       The two halves of the brain and spinal cord are interconnected by numerous fibres that cross the middle line. In some situations such fibres form recognisable bundles that are called commissures. Strictly speaking commissural fibres are those that connect corresponding regions of the two sides. Many of the fibres passing through the socalled commissures do not fulfill this criterion as they connect different regions of the two sides. Such fibres are really association fibres. We have seen that several tracts passing through the spinal cord and brainstem cross from one side to the other. These crossings are  decussations , but collections of such fibres are sometimes loosely referred to as commissures e.g., the ventral white commissure of the spinal cord. The Corpus Callosum        The corpus callosum is the largest commissure connecting the right and left cerebral hemispheres.   ...