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Reading Wikipedia's article of dendrodendritic synapse, I find that:

Dendrodendritic synapses are activated in a similar fashion to axodendritic synapses in respects to using a chemical synapse. These chemical synapses receive a depolarizing signal from an incoming action potential which results in an influx of calcium ions that permit release of Neurotransmitters to propagate the signal the post synaptic cell. There is also evidence of bi-directionality in signaling at dendrodendritic synapses. Ordinarily, one of the dendrites will display inhibitory effects while the other will display excitatory effects.

Now I was wondering, does dendrodendritic synapse occur only when the neuron reaches the threshold action potential and "fires" or is it possible that dendrodendritic synapse occurs as a result of, for example, an axodendritic synapse at the same dendrite? (even though the neuron doesn't fire)

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Clearly, we can see that the dendrite has multiple 'endings'. I was under the impression that a synapse can happen at any such 'ending'. Assuming that a synapse happens at one ending of the dendrite, is it viable that anything happens to a neighbouring neuron that is connected with a dendrodendritic synaptic connection to the other ending of the dendrite?

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I'm not sure if you are asking if an axon that sends a signal to a dendrite would then be released from that dendrite to another dendrite?

I don't see how this is possible seeing as the dendrite is already paired with the axon and downstream of said dendrite there would be a neuron.

A dendrodenritic synapse is two dendrites of two different neurons in contact with each other. For there to be a signal an action potential must have been reached.

Synapse is a junction between two neurons where chemical signaling occurs, but it is not the definition of a signal occurring. If that makes sense.

It seems like you are confused on the location and anatomy of a synapse.

There wouldn't be an axodendritic synapse followed by a dendrodendritic synapse then the neuron. It would either be axodendritic or dendrodendritic. Now there can be multitudes of connections between neurons but I don't think that is what you were asking.

Edit: Seeing your edit makes your question much clearer.

If the signal from the axodendritic synapse excites the neuron enough to reach action potential then that signal would be sent out through its synapses, including the dendrodendritic ones. So I guess in this way it was a "consequence" of the axodendritic synapse.

Though I would rather you think about it in that the action potential of one neuron sent a signal through it's connections to the neighborhing neuron, thus causing that neuron to reach action potential and further send out the signal. It's not really a "consequence" of the synapse, the synapse is more a pathway for the signal to travel.

The stimulus for the action potential is what causes a signal to fire and travel through a synapse.

Hopefully that answers your question.

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  • $\begingroup$ Yes, I might be confused. Thank you for your answer, I think you are right. See my edit for further explanation. $\endgroup$ – Jean-Paul Nov 13 '15 at 20:28
  • $\begingroup$ It does indeed answer my question. I already understood your answer, but I wanted to make absolutely sure that a dendrite cannot cause a synapse to another neuron if the initial neuron didn't fire. $\endgroup$ – Jean-Paul Nov 17 '15 at 11:50

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