Editing Neuron (section)

===Neuron doctrine===
[[File:PurkinjeCell.jpg|thumb|Drawing of neurons in the pigeon [[cerebellum]], by Spanish neuroscientist [[Santiago Ramón y Cajal]] in 1899. (A) denotes [[Purkinje cell]]s and (B) denotes [[granule cells]], both of which are multipolar.]]
The neuron doctrine is the now fundamental idea that neurons are the basic structural and functional units of the nervous system. The theory was put forward by Santiago Ramón y Cajal in the late 19th century. It held that neurons are discrete cells (not connected in a meshwork), acting as metabolically distinct units.

Later discoveries yielded refinements to the doctrine. For example, [[Neuroglia|glial cells]], which are non-neuronal, play an essential role in information processing.<ref>{{cite journal | vauthors = Witcher MR, Kirov SA, Harris KM | title = Plasticity of perisynaptic astroglia during synaptogenesis in the mature rat hippocampus | journal = Glia | volume = 55 | issue = 1 | pages = 13–23 | date = January 2007 | pmid = 17001633 | doi = 10.1002/glia.20415 | citeseerx = 10.1.1.598.7002 | s2cid = 10664003 }}</ref> Also, electrical synapses are more common than previously thought,<ref>{{cite journal | vauthors = Connors BW, Long MA | title = Electrical synapses in the mammalian brain | journal = Annual Review of Neuroscience | volume = 27 | issue = 1 | pages = 393–418 | year = 2004 | pmid = 15217338 | doi = 10.1146/annurev.neuro.26.041002.131128 | url = https://zenodo.org/record/894386 }}</ref> comprising direct, cytoplasmic connections between neurons; In fact, neurons can form even tighter couplings: the squid giant axon arises from the fusion of multiple axons.<ref>{{cite journal | vauthors = Guillery RW | title = Observations of synaptic structures: origins of the neuron doctrine and its current status | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 360 | issue = 1458 | pages = 1281–307 | date = June 2005 | pmid = 16147523 | pmc = 1569502 | doi = 10.1098/rstb.2003.1459 }}</ref>

Ramón y Cajal also postulated the Law of Dynamic Polarization, which states that a neuron receives signals at its dendrites and cell body and transmits them, as action potentials, along the axon in one direction: away from the cell body.<ref name="sabb">{{cite journal | vauthors = Sabbatini RM | date = April–July 2003 | url = http://www.cerebromente.org.br/n17/history/neurons3_i.htm | title = Neurons and Synapses: The History of Its Discovery | journal = Brain & Mind Magazine | pages = 17 }}</ref> The Law of Dynamic Polarization has important exceptions; dendrites can serve as synaptic output sites of neurons<ref>{{cite journal | vauthors = Djurisic M, Antic S, Chen WR, Zecevic D | title = Voltage imaging from dendrites of mitral cells: EPSP attenuation and spike trigger zones | journal = The Journal of Neuroscience | volume = 24 | issue = 30 | pages = 6703–14 | date = July 2004 | pmid = 15282273 | pmc = 6729725 | doi = 10.1523/JNEUROSCI.0307-04.2004 | hdl = 1912/2958 }}
</ref> and axons can receive synaptic inputs.<ref>{{cite journal | vauthors = Cochilla AJ, Alford S | title = Glutamate receptor-mediated synaptic excitation in axons of the lamprey | journal = The Journal of Physiology | volume = 499 | issue = Pt 2 | pages = 443–57 | date = March 1997 | pmid = 9080373 | pmc = 1159318 | doi = 10.1113/jphysiol.1997.sp021940 }}</ref>