Electrical synapse

An electrical synapse, or gap junction, is a mechanical and electrically conductive synapse, a functional junction between two neighboring neurons. The synapse is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction. At gap junctions, such cells approach within about 3.8 nm of each other, a much shorter distance than the 20- to 40-nanometer distance that separates cells at a chemical synapse. In many^[specify] animals, electrical synapse-based systems co-exist with chemical synapses.

Compared to chemical synapses, electrical synapses conduct nerve impulses faster and provide continuous-time bidirectional coupling via linked cytoplasm. As such, the notion of signal directionality across these synapses is not always defined. They are known to produce synchronization of network activity in the brain and can create chaotic network level dynamics. In situations where a signal direction can be defined, they lack gain (unlike chemical synapses)—the signal in the postsynaptic neuron is the same or smaller than that of the originating neuron.^{[citation needed]} The fundamental bases for perceiving electrical synapses comes down to the connexons that are located in the gap junction between two neurons. Electrical synapses are often found in neural systems that require the fastest possible response, such as defensive reflexes. An important characteristic of electrical synapses is that they are mostly bidirectional, allowing impulse transmission in either direction.

Each gap junction (sometimes called a nexus) contains numerous gap junction channels that cross the plasma membranes of both cells. With a lumen diameter of about 1.2 to 2.0 nm, the pore of a gap junction channel is wide enough to allow ions and even medium-size molecules like signaling molecules to flow from one cell to the next, thereby connecting the two cells' cytoplasm. Thus when the membrane potential of one cell changes, ions may move through from one cell to the next, carrying positive charge with them and depolarizing the postsynaptic cell.

Gap junction channels are composed of two hemichannels called connexons in vertebrates, one contributed by each cell at the synapse. Connexons are formed by six 7.5 nm long, four-pass membrane-spanning protein subunits called connexins, which may be identical or slightly different from one another.

An autapse is an electrical (or chemical) synapse formed when the axon of one neuron synapses with its own dendrites.

They are found in many regions in animal and human body. The simplicity of electrical synapses results in synapses that are fast, but more importantly the bidirectional coupling can produce very complex behaviors at the network level.

The relative speed of electrical synapses also allows for many neurons to fire synchronously. Because of the speed of transmission, electrical synapses are found in escape mechanisms and other processes that require quick responses, such as the response to danger of the sea hare Aplysia, which quickly releases large quantities of ink to obscure enemies' vision.

Normally, current carried by ions could travel in either direction through this type of synapse. However, sometimes the junctions are rectifying synapses, containing voltage-gated ion channels that open in response to depolarization of an axon's plasma membrane, and prevent current from traveling in one of the two directions. Some channels may also close in response to increased calcium (Ca²⁺
) or hydrogen (H⁺
) ion concentration, so as not to spread damage from one cell to another.