Final answer:
Both options A and C are true about IPSPs and EPSPs; they can sum together and are types of graded potentials which affect the overall membrane potential depending on their nature and the total voltage change they produce.
Step-by-step explanation:
The student's question relates to the characteristics of inhibitory postsynaptic potentials (IPSPs) and excitatory postsynaptic potentials (EPSPs) in neurons. The two options provided are correct as they are indeed characteristics of IPSPs and EPSPs. To address the student's question, both A and C are true. IPSPs and EPSPs are forms of graded potentials, which are temporary changes in the membrane voltage that can be depolarizing or hyperpolarizing depending on the specific ion channels that are activated.
These graded potentials can sum together, termed summation, to influence the overall membrane potential of a neuron. Summation can be either spatial, involving multiple graded potentials at different locations of the neuron, or temporal, involving multiple graded potentials over time. When sufficient EPSPs accumulate, they can depolarize the membrane to reach the threshold potential, leading to an action potential. Conversely, the presence of IPSPs can move the membrane potential further away from threshold and inhibit the occurrence of an action potential. If the total change in voltage in the membrane is enough to reach the threshold, then the neuron will fire an action potential. This reflects the importance of the balance between EPSPs and IPSPs in the regulation of neuronal activity.