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Encyclopedia > Electrical synapse
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An electrical synapse is a mechanical and electrically conductive link between two abutting neurons that is formed at a narrow gap between the pre- and postsynaptic cells known as a gap junction. At gap junctions, cells approach within about 3.5 nm of each other (Kandel et al., 2000, p. 179), a much shorter distance than the 20 to 40 nm distance that separates cells at chemical synapses (Hormuzdi et al., 2004). It has been suggested that Conductor (power engineering) be merged into this article or section. ... Neurons (also spelled neurones or called nerve cells) are the primary cells of the nervous system. ... Jump to: navigation, search A cell is a single unit or compartment, enclosed by a border or wall. ... A gap junction is a junction between certain animal/plant cell-types that allows different molecules and ions to pass freely between cells. ...


Each gap junction contains numerous gap junction channels which cross the membranes of both cells (Gibson et al., 2004). With a lumen diameter of about 1.2 to 2.0 nm (Bennet and Zukin, 2004; Hormuzdi et al., 2004), the pore of a gap junction channel is wide enough to allow ions and even medium sized molecules like signaling molecules to flow from one cell to the next (Kandel et al., 2000, p. 178-180; Hormuzdi et al., 2004). Thus when the voltage of one cell changes, ions may move through connecting the two cells' cytoplasm from one cell to the next, carrying positive charge with them and depolarizing the postsynaptic cell. Another, unrelated ion channeling process is part of ion implantation. ... Jump to: navigation, search Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Jump to: navigation, search A cell is a single unit or compartment, enclosed by a border or wall. ... In biological cells that are electrically at rest, the cytosol possesses a uniform electric potential or voltage compared to the extracellular solution. ... Jump to: navigation, search An ion is an atom or group of atoms with a net electric charge. ... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ...


Gap junction channels are composed of two hemi-channels called connexons, one contributed by each cell at the synapse (Kandel et al., 2000, p. 178; Bennet and Zukin, 2004; Hormuzdi et al., 2004). Connexons are formed by six 7.5 nm long, six-pass membrane-spanning protein subunits called connexins, which may be identical or slightly different from one another (Bennet and Zukin, 2004). In biology, a connexon is an assembly of 6 proteins called connexins that forms a bridge between the cytoplasm of two adjacent cells. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Connexins are four-pass transmembrane proteins, six of which assemble to form a channel, a connexon. ...


Without the need for receptors to recognize chemical messengers, signaling at electrical synapses is more rapid than that which occurs across chemical synapses, which are the predominant kind of junctions between neurons, though the difference in speed between chemical and electrical synapses is not as important in mammals as it is in cold-blooded animals (Bennet and Zukin, 2004). Thus, electrical synapses are found in escape mechanisms and other processes that require quick responses, such as the goldfish tail-flip response to danger (Kandel et al., 2000). The relative speed of electrical synapses also allows for many neurons to fire synchronously (Kandel et al., 2000, p. 180; Bennet and Zukin, 2004; Gibson et al., 2004). Jump to: navigation, search Illustration of the major elements in a prototypical synapse. ...


Normally current carried by ions could travel in either direction through this type of synapse (Hormuzdi et al., 2004). However, sometimes the junctions are rectifying synapses (Hormuzdi et al., 2004), containing voltage-dependent gates that prevent current from traveling in one of the two directions and open in response to a depolarization (Kandel et al., 2000, p. 180). Some channels may also close in response to increased calcium (Ca++) or hydrogen (H+) ion concentration so as not to spread damage from one cell to another (Kandel et al., 2000, p. 180). Jump to: navigation, search Calcium plays a vital role in the anatomy, physiology and biochemistry of organisms and of the cell, particularly in signal transduction pathways. ...


There is also evidence for "plasticity" at some of these synapses--that is, that the electrical connection they establish can strengthen or weaken as a result of activity. The term synaptic plasticity refers to the variability of the strength of a signal transmitted through a synapse. ...


Electrical synapses are abundant in the retina and cerebral cortex of vertebrates. Human eye cross-sectional view. ... Jump to: navigation, search Location of the Cerebral cortex Slice of the Cerebral cortex, ca. ... Jump to: navigation, search Groups Conodonta Hyperoartia Petromyzontidae (lampreys) Pteraspidomorphi (early jawless fish) Thelodonti Anaspida Cephalaspidomorphi (early jawless fish) Galeaspida Pituriaspida Osteostraci Gnathostomata (jawed vertebrates) Placodermi Chondrichthyes (cartilaginous fish) Acanthodii Osteichthyes (bony fish) Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Tetrapoda Amphibia Amniota Sauropsida/(Reptiles...


History

The model of a reticular network of directly interconnected cells was one of the early hypotheses for the organization of the nervous system at the beginning of the 20th century. This reticular hypothesis was considered to conflict directly with the now predominant neuron doctrine, a model in which isolated, individual neurons signal to each other chemically across synaptic gaps. These two models came into sharp contrast at the award ceremony for the 1906 Nobel Prize in Physiology or Medicine, in which the award went jointly to Camillo Golgi, a reticularist and hugely famous cell biologist, and Santiago Ramón y Cajal, the champion of the neuron doctrine and the father of modern neuroscience. Golgi delivered his Nobel lecture first, in part detailing evidence for a reticular model of the nervous system. Ramón y Cajal then took the podium and refuted Golgi's conclusions in his lecture. Modern understanding of the coexistence of chemical and electrical synapses, however, suggests that both models are physiological significant; it could be said that the Nobel committee acted with great foresight in awarding the Prize jointly. List of Nobel Prize laureates in Physiology or Medicine from 1901 to the present day. ... Camillo Golgi Camillo Golgi (July 7, 1843 - January 21, 1926) was an Italian physician. ... Jump to: navigation, search Santiago Ramón y Cajal Santiago Ramón y Cajal (May 1, 1852–October 17/18, 1934) was a Spanish histologist and is considered to be the father of modern neuroscience. ...


References

  • Bennett M.V. L. and Zukin R. S. 2004. Electrical coupling and neuronal synchronization in the mammalian brain. Neuron, 41(4), 495-511. <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=14980200&dopt=Citation>
  • Gibson J.R., Beierlein M., and ConnorsB.W. 2004. Functional properties of electrical synapses between inhibitory interneurons of neocortical layer 4. Journal of Neurophysiology, 93: 467–480. Available via the World Wide Web: <http://66.102.7.104/search?q=cache:8_SZTPyLGBoJ:www.brown.edu/Research/Connors_Laboratory/publications/J.%2520Neurophysiology/Gibson%2520et%2520al.,%2520J%2520Neurophysiol%25202005.pdf+inhibitory+electrical+synapse&hl=en&client=firefox-a>
  • Hormuzdi S.G., Filippov M.A., Mitropoulou G., Monyer H., and Bruzzone R. 2004. Electrical synapses: a dynamic signaling system that shapes the activity of neuronal networks. Biochimica et Biophysica Acta, 1662(1-2), 113-137. <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15033583&dopt=Citation>
  • Kandel, E.R., Schwartz, J.H., Jessell, T.M. (2000). Principles of Neural Science, 4th ed., pp.178-180. McGraw-Hill, New York.

  Results from FactBites:
 
Synapse - Wikipedia, the free encyclopedia (1111 words)
Synapses are specialized junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands.
A synapse between a motor neuron and a muscle cell is called a neuromuscular junction.
Whether a synapse is excitatory or inhibitory depends on what type(s) of ion channel conduct the post-synaptic current, which in turn is a function of the type of receptors and neurotransmitter employed at the synapse.
  More results at FactBites »

 
 

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