Projection fibers of telencephalon
Fibrae projectionis telencephali
Definition
The projection fibres of telencephalon are white-matter fibres that connect the cerebral cortex with subcortical structures, including the thalamus and basal regions of the forebrain, as well as the brainstem and spinal cord. Unlike association fibres, which connect cortical areas within the same hemisphere, and commissural fibres, which connect the two cerebral hemispheres, projection fibres provide communication between the cerebral cortex and structures at different levels of the central nervous system.
Projection fibres may be ascending or descending.
Ascending projection fibres carry information towards the cerebral cortex; an important example is the thalamocortical fibres, which pass from the thalamus to different cortical areas.
Descending projection fibres carry signals from the cerebral cortex to lower centres. Examples include corticospinal, corticonuclear (corticobulbar) and corticopontine fibres.
Within the cerebral hemispheres, projection fibres of telencephalon have a characteristic arrangement. Superiorly, they spread out in a fan-shaped manner as the corona radiata. As they descend, the fibres converge and become densely packed within the internal capsule. Different projection systems occupy different parts of the internal capsule according to their origins and destinations.
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