An electrical synapse involves a direct connection between two cells where ions can flow between the cells unimpeded i.e a direct electrical connection. Due to this direct connection there is no delay between the signal from one neuron and that being transmitted to the postsynaptic neuron.
So, if we have an action potential in cell 1 (cell on top) we can record its voltage and it will appear like this:
And in cell two, we would record a signal that looks almost exactly the same because it's gone directly through this electrical synapse. It's a bit smaller, however, because there's intrinsic resistance in this electrical synapse (gap junction), so the voltage is reduced, but we can see there's no time delay (look at x axis) between the two signals:
So as you can imagine, it's really good for fast transmission. Another property of an electrical synapse is that it is bidirectional. This is because the gap junctions form open channels that connect the cytoplasm of two neurons directly, allowing ionic current to move based on the electrochemical gradient. This means that the voltage in cell 2 would travel immediately to cell 1.
The pros of this is that it allows for synchronization meaning that groups of neurons can fire together/in a coordinated rhythm.
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Because electrical synapses allow direct and very fast passage of electrical current, when one neuron becomes active, it can instantly depolarize its neighbors through the gap junctions.
So instead of one neuron firing and the rest catching up later (as with slower chemical synapses), they all reach threshold together and fire in unison.
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However, the bidirectionality can lead to uncontrolled spread of electrical activity because there is no filtering like in one-way chemical synapses.