What is the chemical secreted into the gap between neurons at a synapse called?

Answer: Neurotransmitter

Explanation:

Neurotransmitter are refers to as chemical messengers, which are secreted by the nerves cells, to stimulate neighbouring neuron, thereby allowing impulses to be passed from one cell to next, throughout the entire nervous system. Neurotransmitter are released by the axon terminal, after an action potential has reached the synapse, which the is the neuron transmit signal. Neurotransmitter are often released when, electric signal gets to neuron, it triggers the vesicles that contains neurotransmitters, which will split neurotransmitters into the synapse.