VAN 121: Veterinary Gross Anatomy-II (2+2)

CORTICAL CENTRES OF BRAIN

• In each hemisphere, the cortical areas have been identified depending on their action. They are
  • The motor area is the anterior and posterior sigmoid gyri which wind round the crucial fissure as their axis.
  • Coronal gyrus contains the somaesthetic area and is located below and lateral to the coronal sulcus.
  • The postsylvian gyrus contains the auditory area that is between the middle and posterior branches of the sylvian fissure.
  • The lingual gyrus containing the visual area is on the tentorial face of the cerebral hemisphere between the anterior and posterior calcarine fissure.
  • The gyrus fornicatus is double and lies on the medial face of the hemisphere between the callosal and calloso-marginal fissure. In this gyrus the area for taste is located in its upper part and the area for smell is located in its lower part which is continuous with the hippocampal gyrus.

• When the upper part of the cerebral hemisphere is sliced away gradually upto the cingular gyrus, it will be noted that in each hemisphere, there is a peripheral layer of gray mater and a central mass of white mater. When the two hemispheres are gently pulled apart a mass of white mater can be seen below the level of callosal fissure extending from one hemisphere to another. This is the corpus callosum that becomes fully exposed on removing gray mater on the lateral aspects of the corpus callosum.
• The gray mater is the outer layer of the cerebral mass and is composed of nerve cells.
• The white mater is composed of medullated nerve fibres supported by neuroglia. These are
  • Commissural fibres: corpus callosum, anterior and posterior commissures that connect the two cerebral hemispheres.
  • Association fibres: Short or long, connect different parts of the cortical substance in each hemisphere. E.g., cingulum superior, longitudinal fasciculus, inferior longitudinal fasciculus, uncinate fasciculus and fronto-occipital fasciculus.
  • Projection fibres: connecting the cerebral cortex with the medulla and spinal cord, E.g., fibres of the internal capsule.
• Due to lack of pores and tight junctions in the wall of the capillaries of the central nervous system, diffusion of materials to the parenchyma is either stopped or restricted. This so called obstruction between the blood and CNS parenchyma is known as blood- brain barrier.