Purkinje neuron

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Fig. 1: Drawing of Purkinje cells (A) and granule cells (B) from pigeon cerebellum by Santiago Ramón y Cajal, 1899. Instituto Santiago Ramón y Cajal, Madrid, Spain. [1]

Purkinje cells (or Purkinje neurons) are neurons found in all vertebrates.

Basic information

Purkinje cells are neurons located in the Purkinje and Molecular Layers of the vertebrate cerebellar cortex. These cells receive input from parallel fibers and climbing fibers, making 100,000 to 200,000 dendritic connections. Purkinje cells integrate this large number of input signals and provide feedback into the deep cerebellar nuclei, regulating the effect that other cells have on the deep nuclei. This effectively means that Purkinje cells control the sole output of motor coordination in the cerebellum.

Anatomy

The elaborate, nearly two-dimensional dendritic arbors of Purkinje cells make them some of the largest neurons in the human brain. These dendritic arbors consist of hundreds of spiny branches lying within a plane. The cell bodies are located in the Purkinje (middle) Layer of the cerebellar cortex, while the dendrites extend, stacking closely together, into the Molecular (outermost) Layer.

Molecular profile

  • Neurotransmitter: Gamma-aminobutyric acid (GABA), which is the primary inhibitory neurotransmitter in the mammalian central nervous system, performs essential functions in regulating neuronal excitability. GABA is involved in the regulation of both chloride and potassium ion channels.

Physiology

Fig. 2: 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.

Synaptic Connections

Synaptic Inputs

Parallel fibers, the T-shaped axons of granule cells in the Granular (innermost) Layer of the cerebellar cortex, pass orthogonally through the flat layers of Purkinje dendritic arbors. The parallel fibers form excitatory synapses in the Purkinje cell dendrite. Though these synapses are relatively weak in comparison with other synapses on the Purkinje cells, a single Purkinje cell may form synapses with up to 200,000 parallel fibers.

Climbing fibers, neuronal projections from the inferior olivary nucleus in the medulla, form powerful excitatory synapses to the proximal dendrites and cell soma of Purkinje cells. Purkinje cells synapse with multiple climbing fibers early in development. As the cerebellum matures, these synapses are gradually eliminated. The result is that each Purkinje cell receives a synapse from only a single climbing cell, though a single climbing cell forms synapses with 1-10 Purkinje cells.

Basket and stellate cells (located in the cerebellar Molecular Layer) contribute inhibitory input to Purkinje cells. Basket cells synapse on the initial segment of the axon. Stellate Cells synapse onto the dendrites.

Synaptic Outputs

Purkinje cells provide inhibitory feedback into the deep cerebellar nuclei, regulating the effect of climbing and mossy fibers (Fig. 2).

Spiking properties

Purkinje cells show two distinct spiking patterns:

• Simple spikes occur at rates of 17 - 150 Hz either spontaneously or and when Purkinje cells are activated by the parallel fibers. These spikes have a fixed action potential.

• Complex spikes are rapid (>300 Hz) bursts of several spikes with progressively diminishing action potential. These spikes are induced by climbing fiber activation, and can involve the generation of calcium-mediated action potentials in the dendrites.

References

  1. Lee KJ, Kim H, Rhyu IJ. The roles of dendritic spine shapes in Purkinje cells. Cerebellum. 2005;4(2):97-104. Review. PMID: 16035191
  2. Sugihara I. Organization and remodeling of the olivocerebellar climbing fiber projection. Cerebellum. 2006;5(1):15-22. Review. PMID: 16527759
  3. Beierlein M, Regehr WG. Conventional synapses for unconventional cells. Neuron. 2005 Jun 2;46(5):694-6. Review. PMID: 15924854
  4. Hartmann J, Konnerth A. Determinants of postsynaptic Ca2+ signaling in Purkinje neurons. Cell Calcium. 2005 May;37(5):459-66. Review. PMID: 15820394
  5. Schmolesky MT, De Zeeuw CI, Hansel C. Climbing fiber synaptic plasticity and modifications in Purkinje cell excitability. Prog Brain Res. 2005;148:81-94. Review. PMID: 15661183

Additional information

  1. Wikipedia Purkinje Cell [2]
  2. Wikipedia Cerebellum [3]
  3. Wikipedia Climbing fiber [4]
  4. NeuronDB representation of a Purkinje Neuron
  5. Cell Centered Data Base list of Purkinje Neurons
  6. Pubmed search for Purkinje Neuron
  7. Wikipedia entry on Purkinje Neuron