Question

Through the exchange of small metabolites and ions, gap junctions provide metabolic and electrical coupling between cells. Why, then, do you suppose that neurons communicate primarily through synapses rather than through gap junctions?

Answer 1

If action potential spreads through gap junctions, the ions flow directly between the two cells at an extremely fast rate, leading to an unbroken transmission channel. The disadvantage of this type of transmission is that there is no scope for regulation, and there is no gap for depolarization between two successive potentials if they occur immediately.

However, using chemical neurotransmitters, inhibition or delay can be created. There is precise regulation also possible since different transmitters work for different durations and send a different amplitude of signal. That means, a chemical signal can be fine tuned according to the need whereas sending a direct electrical signal does not allow for finetuning.

One more advantage is that gap junctions may transmit signal in both direction due to their continuity, whereas chemical synapses are unidirectional. The neuron that secretes the transmitter sends the signal and the other cell receives it with the help of receptors to the chemical signal.

Another advangate is that one set of ionic currents can be transformed into any other set, thus translating a signal to either excitatory or inhibitory.