Electrical feedback in chemical synapses and the efficacy of synaptic transmission grow with the increase in the gap resistance, so they should be higher in invaginated synapses than in the flat ones. So the plastic changes in the invagination depth may provide a morphological basis for long-term changes in synaptic efficacy: long-term potentiation (LTP) in brain and retinal synapses. In retinal photoreceptor triad synapses, the electrical feedback can provide an "operational" (instantaneous) control of synaptic transmission.