Inhibitory neurotransmitters do what?

• A. Initiate impulses
• B. Block conduction
• C. Decrease impulse
• D. Increase impulse

Answer: (C)

When inhibitory neurotransmitters act, they dampen the postsynaptic neuron's response by making it harder for an action potential to occur. They do this by hyperpolarizing the membrane, often by opening chloride channels or increasing potassium efflux, which pulls the inside of the cell more negative. With the membrane potential further from the threshold, the neuron is less likely to fire. This is why their effect is to decrease impulse transmission. Examples include GABA in the brain and glycine in the spinal cord. In contrast, excitatory transmitters depolarize the membrane and increase the chance of firing, and there’s no direct role in physically blocking conduction along the axon.