it's definitely an electro-chemical gradient of sorts. at the cellular junction i believe the messages being transmitted are mostly receptor based (neurotransmitters) but there possibly some external ionic messages as well. I believe what you're referring to is when an action potential of ionic charge moves up a neuron and triggers the release of neurotransmitters. The message inside the neuron is due to the behavior of ions, and the message externally by receptor-binding neurotransmitters.
