Neuropil

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Neuropil (or "neuropile") is any area in the

White matter, which is mostly composed of myelinated axons (hence its white color) and glial cells, is generally not considered to be a part of the neuropil.^{[citation needed]}

Neuropil (pl. neuropils) comes from the Greek: neuro, meaning "tendon, sinew; nerve" and pilos, meaning "felt".^[2] The term's origin can be traced back to the late 19th century.^[3]

Location

Neuropil has been found in the following regions: outer neocortex layer, barrel cortex, inner plexiform layer and outer plexiform layer, posterior pituitary, and glomeruli of the cerebellum. These are all found in humans, with the exception of the barrel cortex, but many species have counterparts similar to our own regions of neuropil. However, the degree of similarity depends upon the composition of neuropil being compared. The concentrations of neuropil within certain regions are important to determine because simply using the proportions of the different postsynaptic elements does not verify the necessary, conclusive evidence. Comparing the concentrations can determine whether or not proportions of different postsynaptic elements contacted a particular axonal pathway. Relative concentrations could signify a reflection of different postsynaptic elements in the neuropil or show that axons sought out and formed synapses only with specific postsynaptic elements.^[4]

Function

Since neuropils have a diverse role in the nervous system, it is difficult to define a certain overarching function for all neuropils. For instance, the olfactory glomeruli function as sorts of way-stations for the information flowing from the

Neurons are necessary for all connections made in the brain, and thus can be thought of as the "wires" of the brain. As in computing, an entity is most efficient when its wires are optimized; therefore, a brain which has undergone millions of years of natural selection would be expected to have optimized neural circuitry. To have an optimized neural system it must balance four variables—it must "minimize conduction delays in axons, passive cable attenuation in dendrites, and the length of 'wire' used to construct circuits" as well as "maximize the density of synapses",[5] essentially optimizing the neuropil. Researchers at Cold Spring Harbor Laboratory formulated the optimal balance of the four variables and calculated the optimal ratio of axon plus dendrite volume (i.e. the "wire" volume or neuropil volume) to total volume of grey matter. The formula predicted an optimal brain with 3/5 (60%) of its volume occupied by neuropil. Experimental evidence taken from three mouse brains agrees with this result. The "fraction of wire is 0.59 ± 0.036 for layer IV of visual cortex, 0.62 ± 0.055 for layer Ib of piriform cortex, and 0.54 ± 0.035 for the stratum radiatum of hippocampal field CA1. The overall average is 0.585 ± 0.043; these values are not statistically different from the optimal 3/5."^[5]

Clinical significance

Schizophrenia

It has been shown that a certain protein synaptophysin^[6] is lost in people with schizophrenia that causes dendrites and spines to deteriorate in the dorsolateral prefrontal cortex, a part of the neocortex, which plays a key role in information processing, attention, memory, orderly thinking and planning which are all functions that deteriorate in people with schizophrenia. The deterioration of the neuropil in this cortex has been proposed as a contributor to schizophrenia pathophysiology.^{[citation needed]}

Alzheimer's disease

A significant non-human area of neuropil is the barrel cortex found in mammals with whiskers (e.g. cats, dogs and rodents); each "barrel" in the cortex is a region of neuropil where the input from a single whisker terminates.^[9]

Arthropods

The

In chimpanzees and humans the neuropil provides a proxy measure of total connectivity within a local region because it is composed mostly of dendrites, axons, and synapses.[10]

In insects the central complex plays an important role in higher-order brain function. The neuropil in Drosophila Ellipsoid is composed of four substructures. Each section has been observed in several insects as well as the influence it has on

• Axon
• Dendrite
• Dendritic spine
• Glia
• Grey matter
• Neuroanatomy
• Synapse

Citations

This article incorporates text in the public domain from page 1016 of the 20th edition of Gray's Anatomy (1918)

Sources

• Neuropil: Roche Encyclopedia of Medicine, Dictionary Barn.
• Gazzaniga, Richard B. Ivry; Mangun, George R.; Steven, Megan S. (2009). Cognitive neuroscience: the biology of the mind (3rd ed.). New York: W. W. Norton.
  ISBN 978-0-393-92795-5
  .
• Eric R. Kandel; James H. Schwartz; Thomas M. Jessell, eds. (2000). Principles of neural science (4th ed.). New York: McGraw-Hill, Health Professions Division.
  ISBN 978-0-8385-7701-1
  .
• Larry R. Squire; Stephen M. Kosslyn, eds. (1998). Findings and current opinion in cognitive neuroscience. Current Opinion in Neurobiology. Cambridge, Massachusetts: The MIT Press.
  ISBN 978-0-262-69204-5
  .

External links

Look up neuropil in Wiktionary, the free dictionary.

Wikimedia Commons has media related to Neuropil.

• Histology image: 04104loa – Histology Learning System at Boston University—"Nervous Tissue and Neuromuscular Junction: spinal cord, cell bodies of anterior horn cells"
• Neuropil—Cell Centered Database
• Histology image: 3_08 at the University of Oklahoma Health Sciences Center
• "Neuropil—Neural Circuits"—Neuroscience. 2nd edition, Editors: Dale Purves, George J Augustine, David Fitzpatrick, Lawrence C Katz, Anthony-Samuel LaMantia, James O McNamara, and S Mark Williams. Sunderland (MA): Sinauer Associates; 2001.
  ISBN 0-87893-742-0
  .
• https://www.ncbi.nlm.nih.gov/books/NBK11158/