Bruger:Christian89/projekter: Forskelle mellem versioner
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Purkinje celler sender inhibitoriske projektioner til de dybe lillehjerne kerner, og udgør derved det endelige output vedrørende motorisk koordination i lillehjernebarken. |
Purkinje celler sender inhibitoriske projektioner til de dybe lillehjerne kerner, og udgør derved det endelige output vedrørende motorisk koordination i lillehjernebarken. |
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== Elektrofysiologi == |
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[[Image:CerebCircuit.png|thumb|right|200px|Microcircuitry of the cerebellum. [[Excitatory synapses]] are denoted by (+) and [[inhibitory synapses]] by (-).<BR>MF: [[Mossy fiber (cerebellum)|Mossy fiber]].<BR>DCN: [[Deep cerebellar nuclei]].<BR>IO: [[Inferior olivary nucleus|Inferior olive]].<BR>CF: [[Climbing fiber]].<BR>GC: [[Granule cell]].<BR>PF: [[Parallel fiber]].<BR>PC: Purkinje cell.<BR>GgC: [[Golgi cell]].<BR>SC: [[Stellate cell]].<BR>BC: [[Basket cell]].]] |
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Purkinje celler har to forskellige former for elektrofysiologisk aktivitet: |
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* '''Simple spikes''' occur at rates of 17 – 150 Hz (Raman and Bean, 1999), either spontaneously or when Purkinje cells are activated synaptically by the parallel fibers, the axons of the granule cells. |
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* '''Complekse spikes''' are slow, 1–3 Hz spikes, characterized by an initial prolonged large-amplitude spike, followed by a high-frequency burst of smaller-amplitude action potentials. They are caused by climbing fiber activation and can involve the generation of calcium-mediated action potentials in the dendrites. Following complex spike activity, simple spikes can be suppressed by the powerful complex spike input.<ref>Eric R. Kandel, James H. Schwartz, Thomas M. Jessell (2000). ''Principles of Neural Science. 4/e.'' McGraw-Hill. pp.837-40.</ref> |
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Purkinje cells show spontaneous electrophysiological activity in the form of trains of spikes both sodium-dependent and calcium-dependent. This was initially shown by [[Rodolfo Llinas]] (Llinas and Hess (1977) and Llinas and Sugimori (1980). P-type calcium channels were named after Purkinje cells, where they were initially encountered (Llinas et al. 1989), which are crucial in cerebellar function. We now know that activation of the Purkinje cell by climbing fibers can shift its activity from a quiet state to a spontaneously active state and vice-versa, serving as a kind of toggle switch (Loewenstein et al., 2005, Nature Neuroscience). However, these findings have recently been challenged by a study suggesting that such toggling by climbing-fiber inputs occurs predominantly in anaesthetized animals and that Purkinje cells in awake behaving animals, in general, operate almost continuously in the upstate (Schonewille et al., 2006, Nature Neuroscience). |
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Findings have suggested that Purkinje cell dendrites release [[endocannabinoid]]s that can transiently downregulate both excitatory and inhibitory synapses.<ref>{{cite journal |author=Kreitzer AC, Regehr WG |title=Retrograde inhibition of presynaptic calcium influx by endogenous cannabinoids at excitatory synapses onto Purkinje cells |journal=Neuron |volume=29 |issue=3 |pages=717–27 |date=March 2001 |pmid=11301030 |doi=10.1016/S0896-6273(01)00246-X}}</ref> |
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The intrinsic activity mode of Purkinje cells is set and controlled by the [[sodium-potassium pump]].<ref>{{cite journal |author=Forrest MD, Wall MJ, Press DA, Feng J |title=The Sodium-Potassium Pump Controls the Intrinsic Firing of the Cerebellar Purkinje Neuron |journal=PLoS ONE |volume=7 |issue=12 |pages=e51169 |date=December 2012 |pmid=23284664 |pmc=3527461 |url=http://dx.plos.org/10.1371/journal.pone.0051169 |doi=10.1371/journal.pone.0051169 |editor1-last=Cymbalyuk |editor1-first=Gennady}}</ref> This suggests that the pump might not be simply a [[homeostatic]], "housekeeping" molecule for ionic gradients. Instead, it could be a [[computation]] element in the cerebellum and the brain. Indeed, a [[mutation]] in the {{chem|Na|+}}-{{chem|K|+}} pump causes rapid onset dystonia parkinsonism; its symptoms indicate that it is a pathology of cerebellar computation.<ref>{{cite journal |author=Cannon C |title=Paying the Price at the Pump: Dystonia from Mutations in a Na+/K+-ATPase |journal=Neuron |volume=43 |issue=2 |pages=153–154 |date=July 2004 |pmid=15260948 |url=http://www.cell.com/neuron/retrieve/pii/S089662730400426X |doi=10.1016/j.neuron.2004.07.002}}</ref> Furthermore, using the poison [[ouabain]] to block {{chem|Na|+}}-{{chem|K|+}} pumps in the cerebellum of a live mouse induces [[ataxia]] and [[dystonia]].<ref>{{cite journal |author=Calderon DP, Fremont R, Kraenzlin F, Khodakhah K |title=The neural substrates of rapid-onset Dystonia-Parkinsonism |journal=Nature Neuroscience |volume=14 |issue=3 |pages=357–65 |date=March 2011 |pmid=21297628 |pmc=3430603 |url=http://www.nature.com/neuro/journal/v14/n3/full/nn.2753.html |doi=10.1038/nn.2753}}</ref> |
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== Referencer == |
== Referencer == |
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Versionen fra 23. jun. 2014, 21:20
Purkinje celler eller Purkinje neuroner er en type af GABAerge neuroner lokaliseret i lillehjernen. De er opkaldt efter deres tjekkiske opdager Jan Evangelista Purkyně.
Anatomi
Purkinje celler er nogle af de største celler i menneskehjernen (med Betz celler som de største)[1] med et indviklet og detaljeret dendrittræ, som er karakteriseret ved et stort antal af dendritiske fremskud (en: Spines). Purkinje cellerne forekommer i lillehjernens såkaldte Purkinje lag. Purkinje cellerne er placeret foran hinanden som dominobrikker. Deres store dendritiske træ danner nærmest et todimensionelt netværk, hvor parallelfibrer fra de dybere lillehjernelag passerer. Parallelfibrene danner forholdvis svagere excitatoriske (aktiverende) glutaminerge synapser med dendritfremskuddene på dendritttræet, hvorimod klatre fibrer fra nucleus olivarius inferior i medulla oblongata danner et kraftigt excitatorisk input til de proksimale dendritter og cellelegemet. Parallelfibrer passerer ortogonalt gennem Purkinje cellernes dendrittræ med op til 200.000 parallelfibrer,[2] dannende et Granula-celle-Purkinje celle synapse med en enkel Purkinje celle. Hver Purkinje celle modtager ca. 500 klatrefibrersynapser som alle opstår fra en enkel klatrefibre[3]. Både Kurveceller og Stellate celler (lokaliseret i lillehjernens molekylærlag danner inhibitoriske (hæmmende) GABAerge input til Purkinje cellerne, med Kurveceller som synapser på Purkinje cellernes aksonrod og stellate celler på dendritterne.
Purkinje celler sender inhibitoriske projektioner til de dybe lillehjerne kerner, og udgør derved det endelige output vedrørende motorisk koordination i lillehjernebarken.
Referencer
Fodnoter
- ^ Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White (2008). Neuroscience. 4th ed. Sinauer Associates. s. 432-4. ISBN 978-0-87893-697-7.
{{cite book}}: CS1-vedligeholdelse: Flere navne: authors list (link) - ^ Tyrrell, T (1992-05-29). "Cerebellar cortex: its simulation and the relevance of Marr's theory". Philosophical transactions of the Royal Society of London. Series B, Biological sciences. 336 (1277): 239-57. doi:10.1098/rstb.1992.0059. PMID 1353267.
{{cite journal}}: Ukendt parameter|coauthors=ignoreret (|author=foreslået) (hjælp) - ^ Wadiche, JI (2001-10-25). "Multivesicular release at climbing fiber-Purkinje cell synapses". Neuron. 32 (2): 301-13. doi:10.1016/S0896-6273(01)00488-3. PMID 11683999.
{{cite journal}}: Ukendt parameter|coauthors=ignoreret (|author=foreslået) (hjælp)