Projection fiber

 ( Cerebral White Matter ) 

Projection fibers consist of efferent and afferent fibers uniting the Cerebral cortex with the lower parts of the brain and with the spinal cord. In human neuroanatomy, bundles of (nerve fibers) called , within the brain, can be categorized by their function into association tracts, projection tracts, and commissural tracts.

In the neocortex, projection neurons are excitatory neurons that send axons to distant brain targets. Considering the six histologically Cortical layers of the neocortex, associative projection neurons extend axons within one cortical hemisphere; commissural projection neurons extend axons across the midline to the contralateral hemisphere; and corticofugal projection neurons extend axons away from the cortex. That said, some neurons are multi-functional and can therefore be categorized into more than one such category.

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Efferent The principal efferent fibers are:

1. the motor tract, occupying the genu and anterior two-thirds of the occipital part of the internal capsule, and consisting of
2. the corticopontine fibers, ending in the pontine nuclei.

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Afferent The chief afferent fibers are:

1. those of the lemniscus which are not interrupted in the thalamus;
2. those of the superior cerebellar peduncle which are not interrupted in the red nucleus and thalamus;
3. numerous fibers arising within the thalamus, and passing through its stalks to the different parts of the Cerebral cortex;
4. optic and cochlear nerve, the former passing to the Occiput, the latter to the temporal lobe.

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External links

• Diagram at kennedykrieger.org

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