Editing Cerebellum (section)

===== Purkinje layer =====
[[File:PCP4 immunohistochemistry in human cerebellum.jpg|thumb|upright=0.8|Purkinje cells in the human cerebellum (in orange, from top to bottom 40X, 100X and 200X magnification) stained according to published methods<ref name="Felizola et al">{{cite journal | vauthors = Felizola SJ, Nakamura Y, Ono Y, Kitamura K, Kikuchi K, Onodera Y, Ise K, Takase K, Sugawara A, Hattangady N, Rainey WE, Satoh F, Sasano H | title = PCP4: a regulator of aldosterone synthesis in human adrenocortical tissues | journal = Journal of Molecular Endocrinology | volume = 52 | issue = 2 | pages = 159–67 | date = April 2014 | pmid = 24403568 | pmc = 4103644 | doi = 10.1530/JME-13-0248 }}</ref>]]
[[Purkinje cell]]s are among the most distinctive neurons in the brain, and one of the earliest types to be recognized—they were first described by the Czech anatomist [[Jan Evangelista Purkyně]] in 1837. They are distinguished by the shape of their dendritic tree: the dendrites branch very profusely, but are severely flattened in a plane perpendicular to the cerebellar folds. Thus, the dendrites of a Purkinje cell form a dense planar net, through which parallel fibers pass at right angles.<ref name=SOB>{{cite book |title=The Synaptic Organization of the Brain | veditors = Shepherd GM |chapter=Ch. 7 ''Cerebellum'' |year=2004 |publisher=Oxford University Press |location=New York |isbn=978-0-19-515955-4 |vauthors=Llinas RR, Walton KD, Lang EJ }}</ref> The dendrites are covered with [[dendritic spine]]s, each of which receives synaptic input from a parallel fiber. Purkinje cells receive more synaptic inputs than any other type of cell in the brain—estimates of the number of spines on a single human Purkinje cell run as high as 200,000.<ref name=SOB/> The large, spherical cell bodies of Purkinje cells are packed into a narrow layer (one cell thick) of the cerebellar cortex, called the ''Purkinje layer''. After emitting collaterals that affect nearby parts of the cortex, their axons travel into the [[deep cerebellar nuclei]], where they make on the order of 1,000 contacts each with several types of nuclear cells, all within a small domain. Purkinje cells use [[GABA]] as their neurotransmitter, and therefore exert inhibitory effects on their targets.<ref name=SOB/>

Purkinje cells form the heart of the cerebellar circuit, and their large size and distinctive activity patterns have made it relatively easy to study their response patterns in behaving animals using [[extracellular field potential|extracellular]] recording techniques. Purkinje cells normally emit [[action potential]]s at a high rate even in the absence of the synaptic input. In awake, behaving animals, mean rates averaging around 40&nbsp;Hz are typical. The spike trains show a mixture of what are called simple and complex spikes. A simple spike is a single action potential followed by a [[Refractory period (physiology)|refractory period]] of about 10&nbsp;ms; a complex spike is a stereotyped sequence of action potentials with very short inter-spike intervals and declining amplitudes.<ref>{{cite journal | vauthors = Eccles JC, Llinás R, Sasaki K | title = The excitatory synaptic action of climbing fibres on the Purkinje cells of the cerebellum | journal = Journal of Physiology | volume = 182 | issue = 2 | pages = 268–96 | date = January 1966 | pmid = 5944665 | pmc = 1357472 | doi = 10.1113/jphysiol.1966.sp007824 }}</ref> Physiological studies have shown that complex spikes (which occur at baseline rates around 1&nbsp;Hz and never at rates much higher than 10&nbsp;Hz) are reliably associated with climbing fiber activation, while simple spikes are produced by a combination of baseline activity and parallel fiber input. Complex spikes are often followed by a pause of several hundred milliseconds during which simple spike activity is suppressed.<ref name=Simpson>{{cite journal |title=On climbing fiber signals and their consequence(s) |vauthors=Simpson JI, Wylie DR, De Zeeuw CI |journal=Behav. Brain Sci. |volume=19 |year=1996 |pages=384–398 |doi=10.1017/S0140525X00081486 |issue=3}}</ref>

A specific, recognizable feature of Purkinje neurons is the expression of [[calbindin]].<ref>{{cite journal | vauthors = Whitney ER, Kemper TL, Rosene DL, Bauman ML, Blatt GJ | title = Calbindin-D28k is a more reliable marker of human Purkinje cells than standard Nissl stains: a stereological experiment | journal = Journal of Neuroscience Methods | volume = 168 | issue = 1 | pages = 42–7 | date = February 2008 | pmid = 17961663 | doi = 10.1016/j.jneumeth.2007.09.009 | s2cid = 10505177 }}</ref> Calbindin staining of rat brain after unilateral chronic sciatic nerve injury suggests that Purkinje neurons may be [[Adult neurogenesis|newly generated]] in the adult brain, initiating the organization of new cerebellar lobules.<ref name="ReferenceA">{{cite journal | vauthors = Rusanescu G, Mao J | title = Peripheral nerve injury induces adult brain neurogenesis and remodelling | journal = Journal of Cellular and Molecular Medicine | volume = 21 | issue = 2 | pages = 299–314 | date = February 2017 | pmid = 27665307 | pmc = 5264155 | doi = 10.1111/jcmm.12965 }}</ref>
[[File:3 recon 512x512.jpg|thumb|center|A mouse Purkinje cell injected with fluorescent dye]]
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