Final answer:
Neural stimulation that exceeds a threshold triggers an action potential, which is an electrical signal that moves down a neuron's axon.
Step-by-step explanation:
When neural stimulation exceeds a threshold, it triggers an action potential. This electrical signal moves down the neuron's axon as an all-or-none phenomenon, meaning the incoming signal is either sufficient to reach the threshold and cause depolarization or it is insufficient and no action potential occurs. Conversely, the fight or flight response is an involuntary reaction mediated by the nervous and endocrine systems in response to a perceived threat, involving hormones like epinephrine secreted by the adrenal gland. However, this response is not directly triggered by a neural stimulation threshold as is the case with an action potential.