Descending neuron

A descending neuron is a neuron that conveys signals from the brain to motor circuits in the spinal cord (vertebrates) or ventral nerve cord (invertebrates). As the sole conduits of information between the brain and the body, descending neurons play a key role in behavior. Their activity can initiate, maintain, modulate, and terminate behaviors such as locomotion. Because the number of descending neurons is several orders of magnitude smaller than the number of neurons in either the brain or spinal cord/ventral nerve cord, this class of cells represents a critical bottleneck in the flow of information from sensory systems to motor circuits.

Anatomy

Descending neurons have their somas and dendrites (primary input zones) in the brain. Their axons traverse the neck in connectives, or tracts, and output onto neurons in the spinal cord (vertebrates) or ventral nerve cord (invertebrates).

Mammals possess hundreds of thousands of descending neurons.[1][2] They can be divided functionally into two major pathways: pyramidal tracts, which originate in the motor cortex, and extrapyramidal tracts, which originate in the brain stem. An example of the latter is the reticulospinal tract, which is primarily responsible for locomotion and postural control.

Insects possess only hundreds of pairs of descending neurons.[3][4][5][6] Work in the fruit fly Drosophila melanogaster suggests that they are organized into three broad pathways.[6] Two direct pathways link specific regions in the brain to motor circuits in the ventral nerve cord controlling the wings and legs, respectively. A third pathway couples a broad array of brain regions to a large integrative region in the ventral nerve cord that may control both sets of appendages.

Function

Some descending neurons are sufficient to elicit specific coordinated actions.[7][8][9][10][11] One example are the Moonwalker Descending Neurons (MDNs) in the fruit fly Drosophila melanogaster, whose activation elicits backward walking.[9] Another example are the V2a neurons in the mouse, whose activation halts locomotion.[11] However, most behaviors are likely not controlled by single, command-like descending neurons, but by the combined activity of different descending neurons.[12][13]

See also

References
  1. Lemon, Roger N. (July 21, 2008). "Descending Pathways in Motor Control". Annual Review of Neuroscience. 31: 195–218. doi:10.1146/annurev.neuro.31.060407.125547. ISSN 0147-006X. OCLC 57214750.
  2. Liang, Huazheng; Paxinos, George; Watson, Charles (October 9, 2010). "Projections from the brain to the spinal cord in the mouse". Brain Structure and Function. 215: 159–186. doi:10.1007/s00429-010-0281-x. ISSN 1863-2653. LCCN 2007243247. OCLC 804279700.
  3. Okada, Ryuichi; Sakura, Midori; Mizunami, Makoto (March 31, 2003). "Distribution of dendrites of descending neurons and its implications for the basic organization of the cockroach brain". The Journal of Comparative Neurology. 458 (2): 158–174. doi:10.1002/cne.10580. ISSN 0021-9967.
  4. Gal, Ram; Libersat, Frederic (September 2006). "New vistas on the initiation and maintenance of insect motor behaviors revealed by specific lesions of the head ganglia". Journal of Comparative Physiology A. 192 (9): 1003–1020. doi:10.1007/s00359-006-0135-4. ISSN 0340-7594.
  5. Hsu, Cynthia T.; Bhandawat, Vikas (April 2016). "Organization of descending neurons in Drosophila melanogaster". Scientific Reports. 6 (1): 20259. doi:10.1038/srep20259. ISSN 2045-2322. PMC 4738306. PMID 26837716.
  6. Namiki, Shigehiro; Dickinson, Michael H; Wong, Allan M; Korff, Wyatt; Card, Gwyneth M (June 26, 2018). "The functional organization of descending sensory-motor pathways in Drosophila". eLife. 7: e34272. doi:10.7554/eLife.34272. ISSN 2050-084X. PMC 6019073. PMID 29943730.
  7. Kien, Jenny; Altman, Jennifer S. (January 1984). "Descending interneurones from the brain and suboesophageal ganglia and their role in the control of locust behaviour". Journal of Insect Physiology. 30 (1): 59–72. doi:10.1016/0022-1910(84)90108-2.
  8. von Philipsborn, Anne C.; Liu, Tianxiao; Yu, Jai Y.; Masser, Christopher; Bidaye, Salil S.; Dickson, Barry J. (February 2011). "Neuronal Control of Drosophila Courtship Song". Neuron. 69 (3): 509–522. doi:10.1016/j.neuron.2011.01.011.
  9. Bidaye, Salil S.; Machacek, Christian; Wu, Yang; Dickson, Barry J. (April 4, 2014). "Neuronal Control of Drosophila Walking Direction". Science. 344 (6179): 97–101. doi:10.1126/science.1249964. ISSN 0036-8075.
  10. von Reyn, Catherine R; Breads, Patrick; Peek, Martin Y; Zheng, Grace Zhiyu; Williamson, W Ryan; Yee, Alyson L; Leonardo, Anthony; Card, Gwyneth M (July 2014). "A spike-timing mechanism for action selection". Nature Neuroscience. 17 (7): 962–970. doi:10.1038/nn.3741. ISSN 1097-6256.
  11. Bouvier, Julien; Caggiano, Vittorio; Leiras, Roberto; Caldeira, Vanessa; Bellardita, Carmelo; Balueva, Kira; Fuchs, Andrea; Kiehn, Ole (November 2015). "Descending Command Neurons in the Brainstem that Halt Locomotion". Cell. 163 (5): 1191–1203. doi:10.1016/j.cell.2015.10.074. PMC 4899047. PMID 26590422.
  12. Cande, Jessica; Namiki, Shigehiro; Qiu, Jirui; Korff, Wyatt; Card, Gwyneth M; Shaevitz, Joshua W; Stern, David L; Berman, Gordon J (June 26, 2018). "Optogenetic dissection of descending behavioral control in Drosophila". eLife. 7: e34275. doi:10.7554/eLife.34275. ISSN 2050-084X. PMC 6031430. PMID 29943729.
  13. Namiki, Shigehiro; Ros, Ivo G.; Morrow, Carmen; Rowell, William J.; Card, Gwyneth M.; Korff, Wyatt; Dickinson, Michael H. (January 31, 2022). "A population of descending neurons that regulates the flight motor of Drosophila". Current Biology. doi:10.1016/j.cub.2022.01.008. ISSN 0960-9822.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.