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==Anatomi==
==Anatomi==
[[Image:Gray706.png|thumb|200px|left|Transverse section of a cerebellar [[folium (brain)|folium]]. (Purkinje Cell labeled at center top.)]]
[[Image:Gray706.png|thumb|200px|left|Transversalsnit af en foldning i lillehjernen med Purkinje celle angivelsen centralt i toppen af billedet.]]
[[Image:Cerebellum - biel - very high mag.jpg|thumb|left|Purkinje cells. [[Bielschowsky stain]].]]


Purkinje celler er nogle af de største celler i menneskehjenen (med [[Betz celle]]r som de største)<ref name="Purves" >{{cite book | author = Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White | title = Neuroscience. 4th ed. | publisher = Sinauer Associates | pages = 432–4 | year = 2008 | isbn = 978-0-87893-697-7}}</ref> indviklet detaljeret dendrittræ som er karakteriseret ved det store antal af dendritiske fremskud (en: Spines). Purkinje cellerne forekommer i lillehjernens såkaldte Purkinje lag.
Purkinje celler er nogle af de største celler i menneskehjernen (med [[Betz celle]]r som de største)<ref name="Purves" >{{cite book | author = Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White | title = Neuroscience. 4th ed. | publisher = Sinauer Associates | pages = 432–4 | year = 2008 | isbn = 978-0-87893-697-7}}</ref> 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 [[domino]]brikker. Deres store dendritiske træ danner nærmest et todimensionelt netværk, hvor [[parallelfibre]]r fra de dybere lillehjernelag passerer. Parallelfibrene danner forholdvis svagere [[excitatorisk]]e (aktiverende) [[glutamat|glutaminerge]] [[synapse]]r med dendritfremskuddene på dendritttræet, hvorimod [[klatre fibre]]r fra [[nucleus olivarius inferior]] i [[medulla oblongata]] danner et kraftigt excitatorisk input til de [[proksimal]]e dendritter og cellelegemet. Parallelfibrer passerer [[ortogonal]]t gennem Purkinje cellernes dendrittræ med op til 200.000 parallelfibrer,<ref>{{cite journal|last=Tyrrell|first=T|coauthors=Willshaw, D|title=Cerebellar cortex: its simulation and the relevance of Marr's theory.|journal=Philosophical transactions of the Royal Society of London. Series B, Biological sciences|date=1992-05-29|volume=336|issue=1277|pages=239–57|pmid=1353267|doi=10.1098/rstb.1992.0059}}</ref> 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<ref>{{cite journal|last=Wadiche|first=JI|coauthors=Jahr, CE|title=Multivesicular release at climbing fiber-Purkinje cell synapses|journal=Neuron|date=2001-10-25|volume=32|issue=2|pages=301–13|pmid=11683999|doi=10.1016/S0896-6273(01)00488-3}}</ref>. Både [[Kurvecelle]]r og [[Stellate celle]]r (lokaliseret i lillehjernens molekylærlag danner inhibitoriske (hæmmende) [[GABA]]erge input til Purkinje cellerne, med Kurveceller som synapser på Purkinje cellernes [[akson]]rod 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.
Purkinje cells are aligned like [[domino]]s stacked one in front of the other. Their large dendritic arbors form nearly [[two-dimensional]] layers through which [[parallel fiber]]s from the deeper-layers pass. These parallel fibers make relatively weaker [[excitatory synapse|excitatory]] ([[glutamatergic]]) synapses to spines in the Purkinje cell dendrite, whereas [[climbing fibers]] originating from the [[inferior olivary nucleus]] in the [[medulla oblongata|medulla]] provide very powerful excitatory input to the proximal dendrites and cell soma. Parallel fibers pass [[orthogonal]]ly through the Purkinje neuron's dendritic arbor, with up to 200,000 parallel fibers<ref>{{cite journal|last=Tyrrell|first=T|coauthors=Willshaw, D|title=Cerebellar cortex: its simulation and the relevance of Marr's theory.|journal=Philosophical transactions of the Royal Society of London. Series B, Biological sciences|date=1992-05-29|volume=336|issue=1277|pages=239–57|pmid=1353267|doi=10.1098/rstb.1992.0059}}</ref> forming a [[Granule-cell-Purkinje-cell synapse]] with a single Purkinje cell. Each Purkinje cell receives ca 500 climbing fiber synapses, all originating from a single climbing fiber.<ref>{{cite journal|last=Wadiche|first=JI|coauthors=Jahr, CE|title=Multivesicular release at climbing fiber-Purkinje cell synapses|journal=Neuron|date=2001-10-25|volume=32|issue=2|pages=301–13|pmid=11683999|doi=10.1016/S0896-6273(01)00488-3}}</ref> Both basket and stellate cells (found in the cerebellar [[Cerebellum#Molecular Layer|molecular layer]]) provide [[inhibitory]] (GABAergic) input to the Purkinje cell, with basket cells synapsing on the Purkinje cell axon initial segment and stellate cells onto the dendrites.


Purkinje cells send inhibitory projections to the deep cerebellar nuclei, and constitute the sole output of all [[motor coordination]] in the cerebellar cortex.
== Elektrofysiologi ==
== Elektrofysiologi ==
[[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]].]]
[[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]].]]

Versionen fra 23. jun. 2014, 21:17

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

Transversalsnit af en foldning i lillehjernen med Purkinje celle angivelsen centralt i toppen af billedet.

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.

Elektrofysiologi

Microcircuitry of the cerebellum. Excitatory synapses are denoted by (+) and inhibitory synapses by (-).
MF: Mossy fiber.
DCN: Deep cerebellar nuclei.
IO: Inferior olive.
CF: Climbing fiber.
GC: Granule cell.
PF: Parallel fiber.
PC: Purkinje cell.
GgC: Golgi cell.
SC: Stellate cell.
BC: Basket cell.

Purkinje celler har to forskellige former for elektrofysiologisk aktivitet:

  • 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.
  • 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.[4]

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).

Findings have suggested that Purkinje cell dendrites release endocannabinoids that can transiently downregulate both excitatory and inhibitory synapses.[5]

The intrinsic activity mode of Purkinje cells is set and controlled by the sodium-potassium pump.[6] 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 Na+-K+ pump causes rapid onset dystonia parkinsonism; its symptoms indicate that it is a pathology of cerebellar computation.[7] Furthermore, using the poison ouabain to block Na+-K+ pumps in the cerebellum of a live mouse induces ataxia and dystonia.[8]

Referencer

Fodnoter

  1. ^ 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)
  2. ^ 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)
  3. ^ 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)
  4. ^ Eric R. Kandel, James H. Schwartz, Thomas M. Jessell (2000). Principles of Neural Science. 4/e. McGraw-Hill. pp.837-40.
  5. ^ Kreitzer AC, Regehr WG (marts 2001). "Retrograde inhibition of presynaptic calcium influx by endogenous cannabinoids at excitatory synapses onto Purkinje cells". Neuron. 29 (3): 717-27. doi:10.1016/S0896-6273(01)00246-X. PMID 11301030.{{cite journal}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
  6. ^ Forrest MD, Wall MJ, Press DA, Feng J (december 2012). Cymbalyuk, Gennady (red.). "The Sodium-Potassium Pump Controls the Intrinsic Firing of the Cerebellar Purkinje Neuron". PLoS ONE. 7 (12): e51169. doi:10.1371/journal.pone.0051169. PMC 3527461. PMID 23284664.{{cite journal}}: CS1-vedligeholdelse: Dato automatisk oversat (link) CS1-vedligeholdelse: Flere navne: authors list (link)
  7. ^ Cannon C (juli 2004). "Paying the Price at the Pump: Dystonia from Mutations in a Na+/K+-ATPase". Neuron. 43 (2): 153-154. doi:10.1016/j.neuron.2004.07.002. PMID 15260948.{{cite journal}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
  8. ^ Calderon DP, Fremont R, Kraenzlin F, Khodakhah K (marts 2011). "The neural substrates of rapid-onset Dystonia-Parkinsonism". Nature Neuroscience. 14 (3): 357-65. doi:10.1038/nn.2753. PMC 3430603. PMID 21297628.{{cite journal}}: CS1-vedligeholdelse: Dato automatisk oversat (link) CS1-vedligeholdelse: Flere navne: authors list (link)
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