Final answer:
A change in the membrane potential of a neuron from -70 mV to -90 mV is known as an inhibitory postsynaptic potential (IPSP), decreasing the likelihood of firing an action potential.
Step-by-step explanation:
A change in the membrane potential of a postsynaptic neuron from -70 mV to -90 mV is called an inhibitory postsynaptic potential (IPSP). This hyperpolarization moves the membrane potential further away from the threshold, thus decreasing the likelihood that the neuron will fire an action potential. In comparison to a battery's voltage, such as an AA battery's 1.5 V, the changes in membrane potential during an action potential are much less, usually around 0.1 V. Graded potentials can either depolarize or hyperpolarize the membrane, and their sum may lead to reaching the threshold for generating an action potential, if the overall change is sufficiently depolarizing.