What are EPSPs?

• A. Inhibitory signals that decrease chance of firing
• B. Excitatory signals that increase chance of firing
• C. Signals that travel along the axon without decrement
• D. The electrical potential of muscles at rest

Answer: (B)

EPSPs are excitatory postsynaptic potentials—depolarizing changes in the postsynaptic membrane that make it more likely for the neuron to fire an action potential. They occur when excitatory neurotransmitters bind to receptors and open channels that let positive ions (like Na+ or Ca2+) flow into the cell, nudging the membrane potential toward the threshold. These signals are graded and can summate over time (temporal) or across space (spatial), increasing the chance that enough depolarization accumulates to trigger an action potential. This is in contrast to inhibitory signals, which make firing less likely by hyperpolarizing the membrane. EPSPs are not the same as signals that travel along the axon without decrement (that describes action potentials) and they’re not the resting electrical potential of muscles (that’s the resting membrane potential).