Final answer:
Exposure to an excitatory neurotransmitter causes depolarization of the neuron, making it more likely to fire an action potential, while an inhibitory neurotransmitter leads to hyperpolarization, reducing the likelihood of an action potential.
Step-by-step explanation:
When exposed to an excitatory neurotransmitter, like acetylcholine, the membrane potential of a neuron decreases, or depolarizes, due to the influx of Na+ ions through opened ligand-gated channels. This depolarization, referred to as an excitatory postsynaptic potential (EPSP), makes the neuron more likely to fire an action potential. On the contrary, when a neuron is exposed to an inhibitory neurotransmitter, such as GABA, Cl- channels open, leading to an influx of Cl- ions and causing a hyperpolarization of the membrane. This increase in membrane potential, known as an inhibitory postsynaptic potential (IPSP), makes the neuron less likely to fire an action potential. These processes are essential in neurotransmission, influencing how signals are propagated or inhibited throughout the nervous system.