In:
eLife, eLife Sciences Publications, Ltd, Vol. 5 ( 2016-07-06)
Abstract:
The brain is far away from the muscles that it controls. In humans, for example, the brain must be able to trigger the contraction of muscles that are more than a meter away. This task falls to specialized motor neurons that stretch from the brain to the spinal cord, and from the spinal cord to the muscles. Neurons transmit information (in the form of electrical nerve impulses) along their length through cable-like structures called axons. The axons of the motor neurons are so long that, if they were ‘naked’, it would take at least a second for nerve impulses to travel their entire length. Such a long delay between thoughts and actions would make rapid movement impossible. Nerve impulses are able to travel from the brain to the muscles much more quickly, because they are wrapped with a substance called myelin that acts like electrical insulation. Myelin helps the nerve impulses travel up to 100 times faster down the axon. Not surprisingly, diseases that damage myelin, such as multiple sclerosis, severely disrupt movement and sensation. Not all of the brain’s myelin is found around the long axons of motor neurons. The outer layer of the brain, known as the cerebral cortex, also contains myelin. However, most neurons within the cerebral cortex are only a few millimeters long. So what exactly is myelin doing there? Micheva et al. have now used electron microscopy and light microscopy to study the neurons in the cortex of the mouse brain. This revealed that up to half of the myelin in some layers of the cortex surrounds the axons of inhibitory neurons (which reduce the activity of the neurons they signal to). Moreover, one particular subtype of inhibitory neuron accounts for most of the myelinated inhibitory axons, namely inhibitory neurons that contain a protein called parvalbumin. Exactly why parvalbumin-containing neurons are myelinated remains a mystery. Myelin covers only short segments of the axons of these neurons, so it would speed up the transmission of signals by less than a millisecond – probably not enough to make a meaningful difference. Parvalbumin-containing neurons often signal frequently, and thus require large amounts of energy. One possibility therefore is that myelin helps to meet these energy requirements or to reduce energy consumption. Further research will be needed to test this and other ideas.
Type of Medium:
Online Resource
ISSN:
2050-084X
DOI:
10.7554/eLife.15784.001
DOI:
10.7554/eLife.15784.002
DOI:
10.7554/eLife.15784.003
DOI:
10.7554/eLife.15784.004
DOI:
10.7554/eLife.15784.005
DOI:
10.7554/eLife.15784.006
DOI:
10.7554/eLife.15784.007
DOI:
10.7554/eLife.15784.008
DOI:
10.7554/eLife.15784.009
DOI:
10.7554/eLife.15784.010
DOI:
10.7554/eLife.15784.011
DOI:
10.7554/eLife.15784.012
DOI:
10.7554/eLife.15784.013
DOI:
10.7554/eLife.15784.014
DOI:
10.7554/eLife.15784.015
DOI:
10.7554/eLife.15784.016
DOI:
10.7554/eLife.15784.017
DOI:
10.7554/eLife.15784.018
DOI:
10.7554/eLife.15784.019
DOI:
10.7554/eLife.15784.020
DOI:
10.7554/eLife.15784.021
DOI:
10.7554/eLife.15784.022
DOI:
10.7554/eLife.15784.023
DOI:
10.7554/eLife.15784.024
DOI:
10.7554/eLife.15784.025
DOI:
10.7554/eLife.15784.028
DOI:
10.7554/eLife.15784.029
Language:
English
Publisher:
eLife Sciences Publications, Ltd
Publication Date:
2016
detail.hit.zdb_id:
2687154-3
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