To excite or inhibit an action potential in a receiving neuron is called

Neurotransmitters

Explanation:

Neurotransmitters play an important role in neural communication. They are chemical messengers that carry messages between nerve cells (neurons) and other cells in your body, influencing everything from mood to involuntary movements. This process is generally referred to as neurotransmission or synaptic transmission.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.