Neural pathway
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A '''neural pathway''' is a [[neural]] tract connecting one part of the [[nervous system]] with another, usually consisting of bundles of elongated, [[myelin]]-insulated [[neuron]]s, known collectively as [[white matter]]. Neural pathways serve to connect relatively distant areas of the [[brain]] or nervous system, compared to the local communication of [[grey matter]].
==Naming of neural pathways==
The first named pathways were evident even in a poorly-preserved gross [[brain]], and were named by the great anatomists of the [[Renaissance]] using cadaver material. Examples of these include the great ''commissures'' of the brain such as the [[corpus callosum]] ([[Latin]], "huge body"), ''anterior commissure'', and ''posterior commissure''. Further examples of this (by no means a complete list) include the [[Corticospinal tract|pyramidal tract]], [[cerebral peduncle|crus cerebri]] ([[Latin]], "leg of the brain"), and ''cerebellar peduncles'' ([[Latin]], "little foot of the [[cerebellum]]"). Note that these names describe the ''appearance'' of a structure but give one no information on its function or location.
Later, as [[neuroanatomy|neuroanatomical]] knowledge became more sophisticated, the trend was toward naming pathways by their origin and termination. For example, the [[nigrostriatal pathway]], which is degenerated in [[Parkinson's disease]], runs from the [[substantia nigra]] ([[Latin]], "black substance") to the [[striatum|corpus striatum]] ([[Latin]], "striped body"). This naming can extend to include any number of structures in a pathway, such that the cerebellorubrothalamocortical pathway originates in the [[cerebellum]], [[synapse]]s in the [[red nucleus]] ("ruber" in Latin), on to the [[thalamus]], and finally terminating in the [[cerebral cortex]].
Sometimes, these two naming conventions coexist. For example, the name "[[Corticospinal tract|pyramidal tract]]" has been mainly supplanted by [[Corticospinal tract|lateral corticospinal tract]] in most texts. Note that the "old" name was primarily descriptive, evoking the [[Great Pyramid of Giza|pyramids]] of antiquity, from the appearance of this neural pathway in the [[medulla oblongata]]. The "new" name is based primarily on its origin (in the primary motor [[cerebral cortex|cortex]], [[Brodmann area]] 4) and termination (onto the [[motoneuron|alpha motor neurons]] of the [[spinal cord]]).
== Functional aspects ==
In general, [[neuron]]s receive information either at their [[dendrite]]s or [[cell body|cell bodies]]. The [[axon]] of a nerve cell is, in general, responsible for transmitting information over a relatively long distance. Therefore, most neural pathways are made up of [[axon]]s. If the [[axon]]s have [[myelin]] sheaths, then the pathway appears bright white because [[myelin]] is primarily [[lipid]]. If most or all of the axons lack [[myelin]] sheaths (i.e., are ''unmyelinated''), then the pathway will appear a darker beige color, which is generally called ''gray'' ([[American English]], or ''grey'' in [[British English]]).
Some neurons are responsible for conveying information over long distances. For example, [[motoneuron|motor neurons]], which travel from the spinal cord to the muscle, can have axons up to a meter in length in humans; the longest axon in the human body is almost two meters long in tall individuals and runs from the great [[toe]] to the [[medulla oblongata]] of the [[brainstem]]. These are archetypical examples of neural pathways.
==Major neural pathways==
* [[arcuate fasciculus]]
* [[cerebral peduncle]]
* [[corpus callosum]]
* [[Corticospinal tract|pyramidal or corticospinal tract]]
Dopamine pathways:
* [[mesocortical pathway]]
* [[mesolimbic pathway]].
* [[nigrostriatal pathway]]
* [[tuberoinfundibular pathway]]
==References==
*Haines DE. ''Neuroanatomy: An Atlas of Structures, Sections, and Systems'' ISBN 0-7817-3736-2.
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[[Category:Nervous system]]
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