In addition to the above neuron classification scheme more recent schemes use connectivity patterns and quantitative morphology (cell body, dendrites and axons) together with biophysical and biochemical parameters 11, 12 as well as information on proteomics and gene expression 13. Conversely, inhibitory neurons have been considered as local cells (interneuron) without obvious axonal projections into the white matter 10. they send out the axons into the white matter in order to reach other cortical or subcortical regions. Furthermore, a large proportion of excitatory neurons are projection neurons, i.e. Excitatory neurons establish type I or asymmetric synapses with the postsynaptic targets whereas inhibitory neurons work via type II or symmetric synapses 8, 9. Another difference between the two basic neuron classes regards their synaptic connections with the postsynaptic targets. Inhibitory neurons receive input synapses on the dendritic shaft that, from the point of view of signal integration, differs radically from that of spine-bearing dendrites. On the other hand, there is a large variety of non-spiny or smooth dendritic neurons 5, 6 which are inhibitory in nature and contain the neurotransmitter GABA 7. Another characteristic feature of excitatory neurons is that their dendrites bear spines each representing a postsynaptic surface mainly to excitatory inputs arriving either from nearby excitatory neurons or from neurons of other cortical/subcortical areas. The excitatory neuron population shows typically a pyramidal morphology although, in layer 4, spiny stellate and star-pyramidal cell morphology is also common 2, 3, 4. In the visual cortex, excitatory neurons are glutamateergic 1 and represent the dominant cell population in all cortical layers except layer 1. The results suggest an integrating role for the layer 6 stellate neuron which projects to a functionally broad range of neurons in the deep cortical layers and to other cortical and/or subcortical regions. Superimposing the axonal field on the orientation map obtained with optical imaging showed a preponderance of boutons to cross-orientations (38%) and an equal representation of iso- and oblique orientations (31%). Nearly half of the postsynaptic dendrites were immunopositive to GABA. Electron microscopy of the boutons revealed that they targeted dendritic spines (78%) and less frequently dendritic shafts (22%). Dendritic length, surface area and volume values were at least 3 times larger than any known cortical neuron types with the exception of giant pyramidal cells of layer 5. The boutons were uniformly distributed along the axon without forming distinct clusters. However, the axon gave off long-range axons up to 2.8 mm from the parent soma in layers 5/6 before entering the white matter. The neuron was selected from a large pool of intracellularly labelled cells based on the large cell body, numerous spine-free dendrites with an overall interneuron morphology. Many will live the whole lifetime of the animal.Here we report the morpho-functional features of a novel type of deep-layer neuron. Generally, once born, neurons do not divide. However, stem cells in the adult brain may regenerate functional neurons throughout the life of an organism. The chain reaction is a strong electrical current called an action potential that flows down the axon to the next synapse.įully differentiated neurons do not divide. If the dendrites get lots of signals from axons, then it sets off a chain reaction. The movement of the charged ions in the dendrite causes an electrical current, which spreads to the soma briefly before being restored to normal. These chemicals cross the synapse to the dendrite, where they trigger the flow of ions into or out of the cell. When electrical impulses reach the end of an axon, they trigger the release of chemicals called neurotransmitters. Ī dendrite from one neuron and an axon from another neuron meet at a synapse, which is a very narrow gap between the two cells. The dendrites carry signals from other neurons into the soma, and the axon carries a single signal from the soma to the next neuron or to a muscle fiber. The signals go into the cell body (or soma).Ī cell may have hundreds of dendrites, but may have only one axon. Please see for interactive versionĭendrites are the branches of neurons that receive signals from other neurons. The dendrites receive a signal, the axon hillock funnels the signal to the initial segment and the initial segment triggers the activity (action potential) that is sent along the axon towards the synapse. Synapses allow neurons to activate other neurons. Schwann cells make activity move faster down axon. The neuron contains dendrites that receives information, a cell body called the soma, and an axon that sends information.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |