Final answer:
A local hyperpolarization moving the membrane potential to -85 mV is described as an Inhibitory Postsynaptic Potential (IPSP), caused by the exit of K+ or entrance of Cl- ions, making the inside of a neuron more negative and hindering the initiation of an action potential.
Step-by-step explanation:
A local hyperpolarization that changes a postsynaptic neuron's membrane from the resting potential to -85 mV is called an Inhibitory Postsynaptic Potential (IPSP). This hyperpolarization occurs because of the movement of ions across the neuron's membrane, specifically when positive ions, like potassium (K+), leave the cell or when negative ions, like chloride (Cl-), enter the cell. As a result, the internal environment of the neuron becomes more negative, moving the membrane potential further away from the threshold needed to trigger an action potential.
The main purpose of this hyperpolarization is to inhibit the neuron from firing an action potential. If the membrane potential moves away from the threshold required to generate an action potential, the neuron is less likely to fire. The process of returning to the resting potential involves various ion channels and is crucial for the neuron's ability to fire again.