Schematic diagram of large myelinated club ending (LMCE) forming a glutamatergic mixed synapse onto a Mauthner cell dendrite. “Large” (50-nm) round, clear synaptic vesicles (with blue stippling for glutamate) are characteristic of excitatory chemical synapses. Long vs. short red arrows indicate bi-directional but asymmetric 4:1 electrical conductance (i.e., electrical rectification), with the preferred direction of current flow (longer arrow) from the postsynaptic to the presynaptic compartment. In the gap junction, the connexins have 100% asymmetric distribution in apposing hemiplaques, with Cx35 present only in axon terminal hemiplaques (green connexons) and Cx34.7 only in somatic and dendritic hemiplaques (blue connexons), as previously described (Rash et al., 2013). Yellow arrows indicate unidirectional chemical synaptic transmission. Myelin = beige overlay; LMCE = green overlay, dendrite = blue overlay, yellow ovals = glutamate receptors.