Editing Dentate gyrus (section)

==Structure==
[[File:Cerebral Gyri - Medial Surface2.png|thumb|Location of the dentate gyrus and relations to other structures.]]

The dentate gyrus, like the hippocampus, consists of [[archicortex|three distinct layers]]: an outer molecular layer, a middle granule cell layer, and an inner polymorphic layer.<ref>{{cite journal |last1=Treves |first1=A. |last2=Tashiro |first2=A. |last3=Witter |first3=M.P. |last4=Moser |first4=E.I. |title=What is the mammalian dentate gyrus good for? |journal=Neuroscience |date=July 2008 |volume=154 |issue=4 |pages=1155–1172 |doi=10.1016/j.neuroscience.2008.04.073 |pmid=18554812 |s2cid=14710031 }}</ref> The polymorphic layer is also the '''hilus''' of the dentate gyrus (originally named as CA4, the junction of the hippocampus and dentate gyrus).<ref name="Scharfman2">{{cite journal |last1=Scharfman |first1=Helen E. |title=The enigmatic mossy cell of the dentate gyrus |journal=Nature Reviews Neuroscience |date=September 2016 |volume=17 |issue=9 |pages=562–575 |doi=10.1038/nrn.2016.87 |pmid=27466143 |pmc=5369357 }}</ref><ref name="Haines">{{cite book |last1=Haines |first1=D |last2=Mihailoff |first2=G |title=Fundamental neuroscience for basic and clinical applications |date=2018 |isbn=9780323396325 |page=461 |publisher=Elsevier |edition=Fifth}}</ref> (In the hippocampus the outer layer is the molecular layer, the middle layer is the pyramidal layer, and the inner layer the stratum oriens.) Sometimes the molecular layer and the granule layer are referred to as the '''fascia dentata''', that encloses the hilus or polymorphic layer.<ref name="MorrisAmaral2024">{{cite book |last1=Morris |first1=Richard |last2=Amaral |first2=David |title=The Hippocampus Book |date=2024 |publisher=Oxford University Press Inc |location=New York |isbn=9780190065324 |page=52}}</ref><ref name="Hevner">{{cite journal |last1=Hevner |first1=RF |title=Evolution of the mammalian dentate gyrus. |journal=The Journal of Comparative Neurology |date=15 February 2016 |volume=524 |issue=3 |pages=578–94 |doi=10.1002/cne.23851 |pmid=26179319|pmc=4706817 }}</ref>

The granule layer is between the overlying molecular layer and the underlying hilus (polymorphic layer).<ref name="Tuncdemir">{{cite journal |last1=Tuncdemir |first1=Sebnem Nur |last2=Lacefield |first2=Clay Orion |last3=Hen |first3=Rene |title=Contributions of adult neurogenesis to dentate gyrus network activity and computations |journal=Behavioural Brain Research |date=November 2019 |volume=374 |pages=112112 |doi=10.1016/j.bbr.2019.112112 |pmid=31377252 |pmc=6724741 }}</ref>
The [[granule cell]]s of the granule layer project their axons known as [[mossy fiber (hippocampus)|mossy fiber]]s to make excitatory [[synapse]]s on the [[dendrite]]s of CA3 [[pyramidal neuron]]s. The granule cells are tightly packed together in a laminated manner that dampens the excitability of neurons.<ref name="Nadler">{{cite journal |last1=Nadler |first1=J. Victor |title=The recurrent mossy fiber pathway of the epileptic brain |journal=Neurochemical Research |date=2003 |volume=28 |issue=11 |pages=1649–1658 |doi=10.1023/a:1026004904199 |pmid=14584819 |s2cid=2566342 }}</ref>

Some of the basal dendrites of the granule cells curve up into the molecular layer. Most basal dendrites enter the hilus. These hilar dendrites are shorter and thinner, and have fewer side branches.<ref name="Seress">{{cite journal |last1=Seress |first1=László |last2=Mrzljak |first2=Ladislav |title=Basal dendrites of granule cells are normal features of the fetal and adult dentate gyrus of both monkey and human hippocampal formations |journal=Brain Research |date=March 1987 |volume=405 |issue=1 |pages=169–174 |doi=10.1016/0006-8993(87)91003-1 |pmid=3567591 |s2cid=23358962 }}</ref>

A second excitatory cell type in the hilus is the '''mossy cell''',<ref name="Scharfman2"/> which projects its axons widely along the septotemporal axis (running from the [[septal area]] to the [[temporal lobe]]) with the ipsilateral projection skipping the first 1–2&nbsp;mm near the cell bodies,<ref>{{cite journal | vauthors = Amaral DG, Witter MP | year = 1989 | title = The three-dimensional organization of the hippocampal formation: a review of anatomical data | journal = Neuroscience | volume = 31 | issue = 3| pages = 571–591 | doi = 10.1016/0306-4522(89)90424-7 | pmid = 2687721 | s2cid = 28430607 }}</ref> an unusual configuration, hypothesized to prepare a set of cell assemblies in CA3 for a data retrieval role, by randomizing their cell distribution.<ref>{{cite journal | vauthors = Legéndy CR | year = 2017 | title = On the 'data stirring' role of the dentate gyrus of the hippocampus | journal = Reviews in the Neurosciences | volume = 28 | issue = 6| pages = 599–615 | doi = 10.1515/revneuro-2016-0080 | pmid = 28593904 | s2cid = 3716652 }}</ref>

Between the hilus and the granule cell layer is a region called the [[subgranular zone]] which is a site of adult [[adult neurogenesis|neurogenesis]].<ref name="Tuncdemir"/>

The anteromedial continuation of the dentate gyrus is called the '''tail of the dentate gyrus''', or the '''band of Giacomini'''. Most of the dentate gyrus is not exposed on the surface of the brain but the band of Giacomini is visible, and makes an important landmark of the inferior surface of the [[uncus]].<ref name="Elgendy">{{cite web |last1=Elgendy |first1=Azza |title=Band of Giacomini {{!}} Radiology Reference Article {{!}} Radiopaedia.org |url=https://radiopaedia.org/articles/band-of-giacomini?lang=gb |website=Radiopaedia |date=27 January 2015 |access-date=17 October 2019}}</ref>

===Trisynaptic circuit===
The [[trisynaptic circuit]] consists of excitatory cells (mostly [[stellate cell]]s) in [[Entorhinal cortex#Connections|layer II]] of the [[entorhinal cortex]], projecting to the granule cell layer of the dentate gyrus via the [[perforant path]].<ref name="Sinauer Associates">{{cite book|last1=Blumenfeld|first1=Hal|title=Neuroanatomy through clinical cases|date=2010|publisher=Sinauer Associates|location=Sunderland, Mass.|isbn=978-0878936137|edition= 2nd}}</ref><ref name="Senzai">{{cite journal |last1=Senzai |first1=Yuta |title=Function of local circuits in the hippocampal dentate gyrus-CA3 system |journal=Neuroscience Research |date=March 2019 |volume=140 |pages=43–52 |doi=10.1016/j.neures.2018.11.003 |pmid=30408501 |s2cid=53220907 }}</ref> The dentate gyrus receives no direct inputs from other cortical structures.<ref>{{Cite book|author=Nolte, John |title=The Human Brain: An Introduction to Its Functional Neuroanatomy |edition= fifth|year=2002 |pages=570–573}}</ref> The perforant path is divided into the medial and lateral perforant paths, generated, respectively, at the medial and lateral portions of the entorhinal cortex. The medial perforant path synapses onto the proximal dendritic area of the granule cells, whereas the lateral perforant path does so onto their distal dendrites. Most lateral views of the dentate gyrus may appear to suggest a structure consisting of just one entity, but medial movement may provide evidence of the ventral and dorsal parts of the dentate gyrus.<ref>{{cite journal|author1=Rachel A. Dalley |author2=Lydia L. Ng |author3=Angela L. Guillozet-Bongaarts |journal=Nature Precedings|title=Dentate Gyrus|doi=10.1038/npre.2008.2095.1|year=2008 |doi-access=free }}</ref> The axons of the granule cells, called mossy fibres, make excitatory synaptic connections with the pyramidal cells of CA3 and CA1.<ref name="Senzai"/>