Final answer:
An inhibitory postsynaptic potential (IPSP) is associated with hyperpolarization of the postsynaptic membrane. The correct answer is option 2).
Step-by-step explanation:
An inhibitory postsynaptic potential (IPSP) is associated with hyperpolarization. Hyperpolarization in a postsynaptic potential causes the membrane potential to move away from the threshold required for action potential initiation, making an action potential less likely to occur. For instance, when the neurotransmitter GABA is released, it binds to and opens Cl- channels.
The entry of Cl- ions into the neuron results in hyperpolarization of the postsynaptic membrane which increases the negativity of the membrane potential. This process makes the neuron less likely to fire an action potential. Contrastingly, an excitatory postsynaptic potential (EPSP) leads to depolarization.
Moving the membrane potential towards the threshold and increasing the likelihood of action potential generation. The process of summation, where the net effect of EPSPs and IPSPs determines whether a neuron will reach the threshold for action potential generation, further illustrates the inhibitory role of IPSPs.