- Cerebellum granule cell
Neuron: Cerebellar granule cell
Granule cells, parallel fibers, and flattened dendritic trees of Purkinje cells
Location Cerebellum Function excitatory Neurotransmitter glutamate Morphology small cell with few dendrites Presynaptic connections Mossy fibers and Golgi cells Postsynaptic connections Parallel fibers to cerebellar cortex
Granule cells of the cerebellum are among the smallest neurons in the brain. (The term granule cell is used for several unrelated types of small neurons in various parts of the brain.) Cerebellar granule cells are also easily the most numerous neurons in the brain: in humans, estimates of their total number average around 50 billion, which means that they constitute about 3/4 of the brain's neurons.
The cell bodies are packed into a thick layer at the bottom of the cerebellar cortex. A granule cell emits only four to five dendrites, each of which ends in an enlargement called a dendritic claw. These enlargements are sites of excitatory input from mossy fibers and inhibitory input from Golgi cells.
The thin, unmyelinated axons of granule cells rise vertically to the upper (molecular) layer of the cortex, where they split in two, with each branch traveling horizontally to form a parallel fiber; the splitting of the vertical branch into two horizontal branches gives rise to a distinctive "T" shape. A parallel fiber runs for an average of 3 mm in each direction from the split, for a total length of about 6 mm (about 1/10 of the total width of the cortical layer). As they run along, the parallel fibers pass through the dendritic trees of Purkinje cells, contacting one of every 3-5 that they pass, making a total of 80-100 synaptic connections with Purkinje cell dendritic spines. Granule cells use glutamate as their neurotransmitter, and therefore exert excitatory effects on their targets.
Granule cells receive all of their input from mossy fibers, but outnumber them 200 to 1 (in humans). Thus, the information in the granule cell population activity state is the same as the information in the mossy fibers, but recoded in a much more expansive way. Because granule cells are so small and so densely packed, it has been very difficult to record their spike activity in behaving animals, so there is little data to use as a basis of theorizing. The most popular concept of their function was proposed by David Marr, who suggested that they could encode combinations of mossy fiber inputs. The idea is that with each granule cell receiving input from only 4–5 mossy fibers, a granule cell would not respond if only a single one of its inputs was active, but would respond if more than one were active. This "combinatorial coding" scheme would potentially allow the cerebellum to make much finer distinctions between input patterns than the mossy fibers alone would permit.
- ^ a b c d Llinas RR, Walton KD, Lang EJ (2004). "Ch. 7 Cerebellum". In Shepherd GM. The Synaptic Organization of the Brain. New York: Oxford University Press. ISBN 0-19-515955-1.
- ^ Marr D (1969). "A theory of cerebellar cortex". J. Physiol. Lond. 202: 437–70. PMC 1351491. PMID 5784296. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1351491.
Histology: nervous tissue (TA A14, GA 9.849, TH H2.00.06, H3.11) CNSGeneralOther PNSGeneral Neurons/
TerminationSynapse Human brain, rhombencephalon, metencephalon: cerebellum (TA 14.1.07, GA 9.788) Surface anatomyLobesMedial/lateral Grey matter White matterInternalPeduncles
Wikimedia Foundation. 2010.
Look at other dictionaries:
granule cell — n one of the small neurons of the cortex of the cerebellum and cerebrum … Medical dictionary
Granule cell — Not to be confused with granular cells in the kidney. 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. In neuroscience, granule cells… … Wikipedia
granule cell — I. noun : a connective tissue cell containing cytoplasmic granules that stain intensely with aniline dyes II. noun : one of the small neurons of the cortex of the cerebellum and the cerebrum … Useful english dictionary
granule cell — Type of neuron found in the cerebellum … Dictionary of molecular biology
Cerebellum — This article is about the smaller region in the lower part of the brain. For the large region of the brain, see Cerebrum. Brain: Cerebellum A human brain, with the cerebellum colored in purple … Wikipedia
cerebellum — Part of the vertebrate hindbrain, concerned primarily with somatic motor function, the control of muscle tone and the maintenance of balance. Important model for cell migration in developing mammalian brain owing to well studied migratory pathway … Dictionary of molecular biology
Cell (biology) — Allium cells in different phases of the cell cycle … Wikipedia
Anatomy of the cerebellum — This article gives a detailed description of the anatomy of the cerebellum. The structure of the cerebellum can be viewed at three levels. At the level of large scale anatomy, the cerebellum consists of a tightly folded and crumpled layer of… … Wikipedia
Mossy fiber (cerebellum) — For the bundle of axons within the hippocampus, see Mossy fiber (hippocampus). Figure 5: Microcircuitry of the cerebellum. Excitatory synapses are denoted by (+) and inhibitory synapses by ( ). MF: Mossy fiber. DCN: Deep cerebellar nuclei. IO:… … Wikipedia
Golgi cell — Infobox Anatomy Name = PAGENAME Latin = GraySubject = GrayPage = Caption = Microcircuitry of the cerebellum. Excitatory synapses are denoted by (+) and inhibitory synapses by ( ). MF: Mossy fiber. DCN: Deep cerebellar nuclei. IO: Inferior olive.… … Wikipedia