What type of chemical function leads to a decreased likelihood of action potentials?

The correct answer, indicating an inhibitory function, refers to the role of certain neurotransmitters that reduce the likelihood of action potentials occurring in a neuron. Inhibitory neurotransmitters work by causing hyperpolarization of the postsynaptic membrane, which makes it less likely for the neuron to reach the threshold needed to generate an action potential.

An example of an inhibitory neurotransmitter is gamma-aminobutyric acid (GABA), which opens channels that allow negatively charged ions into the neuron, thus increasing its internal negativity and stabilizing it. This effect counteracts the excitatory signals that, if in excess, could lead to uncontrolled firing of action potentials.

While excitatory functions increase the likelihood of action potential generation by depolarizing the postsynaptic membrane, this option does not apply to the question's focus on decreased likelihood. Neurotransmitters and hormonal functions encompass a broader category where both excitatory and inhibitory types exist, but again, the specificity of inhibition is what is critical here. Therefore, it is the inhibitory function that explicitly reduces the potential for action signaling within the neural circuitry.