Electrical synapse

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).

Related Topics:
Conductive - Neuron - Cell - Gap junction

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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.

Related Topics:
Channel - Membranes - Cell - Voltage - Ion - Cytoplasm

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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, membrane spanning protein subunits called connexins, which may be identical or slightly different from one another (Bennet and Zukin, 2004).

Related Topics:
Connexon - Protein - Connexin

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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).

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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{{sup|++}}) or hydrogen (H{{sup|+}}) ion concentration so as not to spread damage from one cell to another (Kandel et al., 2000, p. 180).

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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.

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Electrical synapses are abundant in the retina and cerebral cortex of vertebrates.

Related Topics:
Retina - Cerebral cortex - Vertebrate

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