If all 15 presynaptic neurons stimulate the post-synaptic neuron at the same time, will an action potential be produced?

Yes

Explanation:

If all 15 presynaptic neurons stimulate the post-synaptic neuron at the same time, the action potential will be produced. In a chemical synapse, an action potential in the presynaptic neuron is responsible for the release of a chemical messenger known as neurotransmitter. After this, the neurotransmitter diffuses across the synapse and binds to the postsynaptic cell so we can say that potential can be produced.

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