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

The type of chemical function that leads to a decreased likelihood of action potentials is inhibitory. Inhibitory functions are associated with neurotransmitters that make a neuron's membrane potential more negative or hyperpolarized, which moves the membrane potential further away from the threshold needed to trigger an action potential.

When an inhibitory neurotransmitter binds to its receptor on a postsynaptic neuron, it often opens channels that allow positively charged ions to exit the neuron or negatively charged ions to enter. This movement of ions increases the membrane potential's negativity, making it less likely that the neuron will reach the threshold required to fire an action potential.

In contrast, excitatory functions typically promote depolarization, which makes an action potential more likely. Neurotransmitters encompass both excitatory and inhibitory types, but they do not denote the effect on action potential likelihood without specifying their nature. Hormonal functions primarily relate to the body’s endocrine system and do not directly influence synaptic transmission in the same immediate way that excitatory and inhibitory neurotransmitters do. Therefore, inhibitory chemical functions are specifically responsible for reducing the probability of action potentials occurring.