Neural pathway

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A neural pathway connects a part of the nervous system to another using bundles of axons called tracts. The optic nerve is an example of a neural pathway because it connects the eye back to the brain.

A neural pathway, is a series of neurons connected together to enable a signal to be sent from one brain region to another.[1] Neurons are connected by a single nerve fibre or by bundles of nerve fibres known as tracts.[2] A neural pathway that serves to connect relatively distant areas of the brain or nervous system is a bundle of neurons, known collectively as white matter.[citation needed] A neural pathway that spans a shorter distance between structures, such as most of the pathways of the major neurotransmitter systems, is usually called grey matter.[citation needed]

In the hippocampus there are neural pathways involved in its circuitry including the perforant pathway, that provides a connectional route from the entorhinal cortex[3] to all fields of the hippocampal formation, including the dentate gyrus, all CA fields (including CA1),[4] and the subiculum.

Descending motor pathways travel form the cerebral cortex to the lower spinal cord.[5]

Naming[edit]

Neural pathways of cerebellar cortex
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] 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" – the "huge" statue), anterior commissure, and posterior commissure.[citation needed] Further examples include the pyramidal tract, crus cerebri (Latin, "leg of the brain"), and cerebellar peduncles (Latin, "little foot of the cerebellum").[citation needed] Note that these names describe the appearance of a structure but give one no information on its function or location.[citation needed]

Later, as neuroanatomical knowledge became more sophisticated, the trend was toward naming pathways by their origin and termination.[citation needed] For example, the nigrostriatal pathway runs from the substantia nigra (Latin, "black substance") to the corpus striatum (Latin, "striped body").[citation needed] This naming can extend to include any number of structures in a pathway, such that the cerebellorubrothalamocortical pathway originates in the cerebellum, synapses in the red nucleus ("ruber" in Latin), on to the thalamus, and finally terminating in the cerebral cortex.[citation needed]

Sometimes, these two naming conventions coexist. For example, the name "pyramidal tract" has been mainly supplanted by lateral corticospinal tract in most texts.[citation needed] Note that the "old" name was primarily descriptive, evoking the pyramids of antiquity, from the appearance of this neural pathway in the medulla oblongata.[citation needed] The "new" name is based primarily on its origin (in the primary motor cortex, Brodmann area 4) and termination (onto the alpha motor neurons of the spinal cord).[citation needed]

In the cerebellum one of the two major pathways is that of the mossy fibers. Mossy fibers project directly to the 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 fibers and these project to Purkinje cells and also send collaterals directly to the deep nuclei.[6]

Functional aspects[edit]

Diagram showing cortical pathways

In general, neurons receive information either at their dendrites or 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 axons.[citation needed] If the axons have myelin sheaths, then the pathway appears bright white because myelin is primarily lipid.[citation needed] 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]

Some neurons are responsible for conveying information over long distances. For example, 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]

Basal ganglia pathways and dopamine[edit]

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 pathways. 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.[7] Dopamine is provided both tonically and phasically in response to the needs of the neural pathways. [7]

Major neural pathways[edit]

See also[edit]

References[edit]

  1. ^ "Neural pathway". Retrieved 24 February 2017. 
  2. ^ Moore, Keith; Dalley, Arthur (2005). Clinically Oriented Anatomy (5th ed.). LWW. p. 47. ISBN 0-7817-3639-0. A bundle of nerve fibers (axons) connecting neighboring or distant nuclei of the CNS is a tract. 
  3. ^ Witter, Menno P.; Naber, Pieterke A.; Van Haeften, Theo; Machielsen, Willem C.M.; Rombouts, Serge A.R.B.; Barkhof, Frederik; Scheltens, Philip; Lopes Da Silva, Fernando H. (2000). "Cortico-hippocampal communication by way of parallel parahippocampal-subicular pathways". Hippocampus. 10 (4): 398–410. PMID 10985279. doi:10.1002/1098-1063(2000)10:4<398::AID-HIPO6>3.0.CO;2-K. 
  4. ^ Vago, David R.; Kesner, Raymond P. (2008). "Disruption of the direct perforant path input to the CA1 subregion of the dorsal hippocampus interferes with spatial working memory and novelty detection". Behavioural Brain Research. 189 (2): 273–83. PMC 2421012Freely accessible. PMID 18313770. doi:10.1016/j.bbr.2008.01.002. 
  5. ^ Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark (1 January 2001). "Damage to Descending Motor Pathways: The Upper Motor Neuron Syndrome". 
  6. ^ Llinas RR, Walton KD, Lang EJ (2004). "Ch. 7 Cerebellum". In Shepherd GM. The Synaptic Organization of the Brain. New York: Oxford University Press. ISBN 0-19-515955-1. 
  7. ^ a b Hong, Simon (2013). "Dopamine system: manager of neural pathways". Frontiers in Human Neuroscience. 7. doi:10.3389/fnhum.2013.00854.