View source for Neural pathway

{{Short description|Connection formed between neurons that allows neurotransmission}}
{{For|circuits of neurons|neural circuit}}
{{Distinguish|Neurotransmitter pathways}}

[[File:Neural_pathway_diagram.svg|thumb|A neural pathway connects one part of the [[nervous system]] to another using bundles of [[axon]]s called tracts. The [[optic tract]] that extends from the [[optic nerve]] is an example of a neural pathway because it connects the eye to the brain; additional pathways within the brain connect to the [[visual cortex]].]]

In [[neuroanatomy]], a '''neural pathway''' is the connection formed by [[axon]]s that project from [[neuron]]s to make [[synapse]]s onto neurons in another location, to enable [[neurotransmission]] (the sending of a signal from one region of the [[nervous system]] to another). Neurons are connected by a single axon, or by a bundle of axons known as a [[nerve tract]], or [[nerve fascicle|fasciculus]].<ref>{{Cite book|title = Clinically Oriented Anatomy|last1 = Moore|first1 = Keith|last2 = Dalley|first2 = Arthur|publisher = LWW|year = 2005|isbn = 0-7817-3639-0|edition = 5th|page = [https://archive.org/details/clinicallyorient00moor_1/page/47 47]|quote = A bundle of nerve fibers (axons) connecting neighboring or distant nuclei of the CNS is a tract.|url-access = registration|url = https://archive.org/details/clinicallyorient00moor_1/page/47}}</ref> Shorter neural pathways are found within [[grey matter]] in the [[brain]], whereas longer projections, made up of [[myelin]]ated axons, constitute [[white matter]].

In the [[hippocampus]], there are neural pathways involved in its circuitry including the [[perforant path]]way,  that provides a connectional route from the [[entorhinal cortex]]<ref name="pmid10985279">{{cite journal |doi=10.1002/1098-1063(2000)10:4<398::AID-HIPO6>3.0.CO;2-K|pmid=10985279|title=Cortico-hippocampal communication by way of parallel parahippocampal-subicular pathways|journal=Hippocampus|volume=10|issue=4|pages=398–410|year=2000|last1=Witter|first1=Menno P.|last2=Naber|first2=Pieterke A.|last3=Van Haeften|first3=Theo|last4=Machielsen|first4=Willem C.M.|last5=Rombouts|first5=Serge A.R.B.|last6=Barkhof|first6=Frederik|last7=Scheltens|first7=Philip|last8=Lopes Da Silva|first8=Fernando H.|s2cid=25432455 }}</ref> to all fields of the [[hippocampal formation]], including the [[dentate gyrus]], all [[hippocampus proper|CA fields]] (including CA1),<ref name="pmid18313770">{{cite journal |doi=10.1016/j.bbr.2008.01.002|pmid=18313770|title=Disruption of the direct perforant path input to the CA1 subregion of the dorsal hippocampus interferes with spatial working memory and novelty detection|journal=Behavioural Brain Research|volume=189|issue=2|pages=273–83|year=2008|last1=Vago|first1=David R.|last2=Kesner|first2=Raymond P.|pmc=2421012}}</ref> and the [[subiculum]].

Descending motor pathways of the [[pyramidal tracts]] travel from the [[cerebral cortex]] to the [[brainstem]] or lower [[spinal cord]].<ref name="Sinauer">{{cite book|last1=Purves|first1=Dale|title=Neuroscience|date=2011|publisher=Sinauer|location=Sunderland, Mass.|isbn=9780878936953|pages=375–378|edition=5.}}</ref><ref name="Purves">{{cite book|last1=Purves|first1=Dale|last2=Augustine|first2=George J.|last3=Fitzpatrick|first3=David|last4=Katz|first4=Lawrence C.|last5=LaMantia|first5=Anthony-Samuel|last6=McNamara|first6=James O.|last7=Williams|first7=S. Mark|title=Damage to Descending Motor Pathways: The Upper Motor Neuron Syndrome|url=https://www.ncbi.nlm.nih.gov/books/NBK10898/|language=en|date=1 January 2001|publisher=Sinauer Associates }}</ref> Ascending [[sensory neuron|sensory]] tracts in the [[dorsal column–medial lemniscus pathway]] (DCML) carry information from the periphery to the cortex of the brain.

==Naming==
[[File:Architecture of the Cerebellar Cortex.svg|thumb|left|380px|Neural pathways of [[cerebellum|cerebellar cortex]] ]]
[[File:Ciliary ganglion pathways.png|thumb|left|Pathways in the [[ciliary ganglion]]. Green=Parasympathetic; Red=Sympathetic; Blue=Sensory]]
The first named pathways are evident to the naked eye even in a poorly preserved [[brain]], and were named by the great anatomists of the [[Renaissance]] using cadaver material.{{Citation needed|date=February 2017}} Examples of these include the great ''commissures'' of the brain such as the [[corpus callosum]] ([[Latin]], "hard body"; not to be confused with the Latin word "colossus"{{snd}} the "huge" statue), ''anterior commissure'', and ''posterior commissure''.{{Citation needed|date=February 2017}} Further examples include the [[Corticospinal tract|pyramidal tract]], [[cerebral peduncle|crus cerebri]] ([[Latin]], "leg of the brain"), and ''cerebellar peduncles'' ([[Latin]], "little foot of the [[cerebellum]]").{{Citation needed|date=February 2017}} Note that these names describe the ''appearance'' of a structure but give no information on its function, location, etc.{{Citation needed|date=February 2017}}

Later, as [[neuroanatomy|neuroanatomical]] knowledge became more sophisticated, the trend was toward naming pathways by their origin and termination.{{Citation needed|date=February 2017}} For example, the [[nigrostriatal pathway]] runs from the [[substantia nigra]] ([[Latin]], "black substance") to the [[striatum|corpus striatum]] ([[Latin]], "striped body").{{Citation needed|date=February 2017}} 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]].{{Citation needed|date=February 2017}}

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.{{Citation needed|date=February 2017}} 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]].{{Citation needed|date=February 2017}} 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]]).{{Citation needed|date=February 2017}}

In the [[cerebellum]], one of the two major pathways is that of the [[mossy fiber (cerebellum)|mossy fiber]]s. Mossy fibers project directly to the [[deep cerebellar nuclei|deep nuclei]], but also give rise to the following pathway: mossy fibers → granule cells → parallel fibers → Purkinje cells → deep nuclei. The other main pathway is from the [[climbing fiber]]s and these project to Purkinje cells and also send collaterals directly to the deep nuclei.<ref name=SOB>{{cite book |title=The Synaptic Organization of the Brain |editor=Shepherd GM |chapter=Ch. 7 ''Cerebellum'' |year=2004 |publisher=Oxford University Press |location=New York |isbn=0-19-515955-1 |vauthors=Llinas RR, Walton KD, Lang EJ }}</ref>

==Functional aspects==
[[File:Posterior Parietal Lobe.jpg|thumb|300px|Diagram showing cortical pathways]]

In general, [[neuron]]s receive information either at their [[dendrite]]s or [[soma (biology)|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.{{Citation needed|date=February 2017}} If the [[axon]]s have [[myelin]] sheaths, then the pathway appears bright white because [[myelin]] is primarily [[lipid]].{{Citation needed|date=February 2017}} 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 ''grey''.{{Citation needed|date=February 2017}}

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 belongs to the Sciatic Nerve and runs from the great [[toe]] to the base of the spinal cord. These are archetypal examples of neural pathways.{{Citation needed|date=February 2017}}

==Basal ganglia pathways and dopamine==
Neural pathways in the [[basal ganglia]] in the [[cortico-basal ganglia-thalamo-cortical loop]], are seen as controlling different aspects of behaviour. This regulation is enabled by the [[dopamine pathway]]s. It has been proposed that the dopamine system of pathways is the overall organiser of the neural pathways that are seen to be parallels of the dopamine pathways.<ref name="Hong">{{cite journal|last1=Hong|first1=Simon|title=Dopamine system: manager of neural pathways|journal=Frontiers in Human Neuroscience|date=2013|volume=7|page=854|doi=10.3389/fnhum.2013.00854|pmc=3856400|pmid=24367324|doi-access=free}}</ref> Dopamine is provided both [[tonic (physiology)|tonically]] and phasically in response to the needs of the neural pathways.<ref name=Hong/>

==Major neural pathways==
* [[Arcuate fasciculus]]
* [[Cerebral peduncle]]
* [[Corpus callosum]]
* [[Pyramidal tracts]]{{snd}} [[corticospinal tract|corticospinal]] and [[corticobulbar tract]]s
* [[Medial forebrain bundle]]
* [[Dorsal column–medial lemniscus pathway]]
* [[Retinohypothalamic tract]] is a photic neural input pathway involved in the [[circadian rhythm]]s

==See also==
* [[Direct pathway of movement]]
* [[Indirect pathway of movement]]
* [[Reflex arc]]
* [[Systems neuroscience]]
* [[Nerve tract]]
* [[Neural circuit]]
* [[Nerve plexus]]

==References==
{{Reflist}}

{{Neural tracts}}
{{Visual pathways}}
{{Auditory and vestibular pathways}}
{{Papez circuit}}
{{Authority control}}

[[Category:Central nervous system pathways| ]]
[[Category:Neural circuitry]]