166 WHITE MATTER OF HEMISPHERIS
* Telencephalon consists of:
- cerebral cortex " grey matter)
- white matter
- Basal ganglia
- White matter of the cerebral cortex consists of 3 types of fibers
- Association fibers:
- These are fibers that connect different regions in the same hemisphere.
- They are either short (arcuate fibers) or long (fasciculi).
- Commisural fibers:
- These are fibers that interconnect and permit communication between both hemispheres.
- They include corpus callosum and other commissures (anterior commissure, posterior commissure.... etc.)
- Projection fibers:
- These are fibers that link the cerebral cortex to the diencephalon, brain stem, cerebellum, and spinal cord.
- These fibers are either ascending or descending.
- They form the corona radiata and internal capsule.
Association fibers:
- Short fibers: they are called arcuate fibers as they curve in an arc to pass from a gyrus to another.
- Long fibers: they are arranged as discrete bundles or fasciculi. They include:
- Superior longitudinal bundle: connecting frontal lobe to occipital and temporal lobes.
- Fronto-occipital bundle: connecting also frontal lobe to occipital and temporal lobes (but runs at a deeper plane than superior longitudinal bundle). It is considered as a part from superior longitudinal bundle separated from it by the corona radiata.
- Inferior longitudinal bundle: connecting frontal lobe to temporal lobe.
- Uncinate bundle: connecting sensory speech area (in the temporal lobe) to motor speech area (in the frontal lobe).
- Cingulum: connecting cingulate gyrus to the para-hippocampal gyrus. It runs deep to the limbic lobe.