Resting Potential in AP Psychology

In AP Psychology, resting potential is the stable, negative charge (about -70mV) inside a neuron that is not sending a signal. The inside of the cell is more negative than the outside, so the neuron is polarized and ready to fire an action potential once stimulation pushes it to threshold.

What is Resting Potential?

Resting potential is what a neuron looks like electrically when it's not firing. The inside of the cell membrane carries a negative charge compared to the outside, usually around -70 millivolts (mV). Because there's a charge difference across the membrane, the neuron is called polarized.

Think of resting potential as a loaded spring. Nothing is happening yet, but the energy is stored and ready. When the neuron gets enough excitatory input, positive charge rushes in. That depolarization pushes the charge up toward threshold (around -55mV). If it reaches threshold, the neuron fires an action potential. Afterward, the neuron goes through a refractory period and resets back to resting potential so it can fire again. The CED lists resting potential as one of the core steps of neural transmission in 1.3.B.1. It also explicitly says the sodium-potassium pump is outside the scope of the AP Psychology Exam, so you only need to know what resting potential is and where it fits in the sequence. You don't need the pump chemistry behind it.

Why Resting Potential matters in AP® Psychology

Resting potential lives in Unit 1: Biological Bases of Behavior, Topic 1.3 The Neuron and Neural Firing. It directly supports learning objective AP Psych 1.3.B (explain how the basic process of neural transmission is related to behavior and mental processes). Essential knowledge 1.3.B.1 names it alongside the all-or-none principle, depolarization, refractory period, reuptake, and threshold.

Why care? Resting potential is the starting line for every neural signal. You can't explain threshold, the all-or-none principle, or why a neuron needs a refractory period without knowing what state the neuron starts from and returns to. It also sets you up for 1.3.C, because psychoactive drugs and disorders like multiple sclerosis change how easily or reliably neurons move from rest to firing.

How Resting Potential connects across the course

Action Potential (Unit 1)

Resting potential and the action potential are two halves of the same story. Resting potential is the neuron "off" and charged up. The action potential is the neuron "on," sending an electrical impulse down the axon. Every action potential starts from rest and ends with a return to rest.

Threshold and the All-or-None Principle (Unit 1)

Threshold is the finish line, and resting potential is the starting line. Going from -70mV to -55mV is the gap a stimulus has to close. If input falls short, the neuron stays at rest and nothing fires. If input crosses threshold, the neuron fires at full strength. That's the all-or-none principle.

Hyperpolarization and the Refractory Period (Unit 1)

Right after firing, the neuron briefly dips even more negative than its resting level. That dip is hyperpolarization. During this refractory period the neuron is harder to fire until it settles back to resting potential. This is why neurons can't fire nonstop.

Psychoactive Drugs and Neural Disorders (Unit 1)

Under 1.3.C, stimulants like caffeine increase neural activity and depressants like alcohol decrease it. Put another way, they change how often neurons leave rest and fire. Disorders like multiple sclerosis disrupt the orderly signal that resting potential sets up, which leads to symptoms like weakness and poor coordination.

Is Resting Potential on the AP® Psychology exam?

Resting potential shows up mostly in multiple-choice questions that test the order and logic of neural firing. Expect these kinds of questions:

• Number-based stems. A question might give you a resting potential of -70mV and a threshold of -55mV, then ask what happens when an excitatory input arrives. You have to reason that the neuron fires only if the input pushes it all the way to threshold, and that it fires at full strength when it does.
• Data-interpretation stems. A study might report firing rates for different stimuli. A stimulus producing 0 action potentials per second means the neuron stayed at resting potential and never reached threshold.
• Disorder applications. Questions about multiple sclerosis ask you to connect a disrupted neural transmission process to behavioral symptoms like impaired coordination.

No released FRQ has used "resting potential" verbatim. Still, it supports the kind of explanation FRQs reward, where you trace how a biological process (neural firing) connects to a behavior. Don't bring up the sodium-potassium pump. The CED excludes it, so it won't earn you points.

Resting Potential vs Action Potential

Resting potential is the neuron at rest. The charge stays steady at about -70mV and no signal is being sent. An action potential is the neuron actively firing, a brief electrical impulse that travels down the axon after the charge reaches threshold. If the question describes a neuron that's waiting, polarized, or not stimulated, think resting potential. If it describes a neuron sending a signal, think action potential.

Key things to remember about Resting Potential

• Resting potential is the negative charge inside a neuron that is not firing, usually about -70mV.

• A neuron at resting potential is polarized, meaning the inside is more negative than the outside.

• Excitatory input depolarizes the neuron, and if the charge reaches threshold (around -55mV), the neuron fires an action potential.

• After firing, the neuron briefly hyperpolarizes during the refractory period and then returns to resting potential.

• Resting potential is part of essential knowledge 1.3.B.1 under learning objective AP Psych 1.3.B in Unit 1.

• The sodium-potassium pump is excluded from the AP Psychology Exam, so focus on the sequence of firing rather than the ion chemistry.

Frequently asked questions about Resting Potential

What is resting potential in AP Psychology?

Resting potential is the stable negative charge inside a neuron when it isn't sending a signal, about -70mV. It's the neuron's ready state, and the action potential starts from it.

Is a neuron at resting potential doing nothing?

Not exactly. It isn't sending a signal, but it is holding a charge difference across its membrane, like a loaded spring. That stored charge is what lets the neuron fire quickly once input pushes it to threshold.

What's the difference between resting potential and action potential?

Resting potential is the neuron at rest, holding steady at about -70mV. An action potential is the neuron firing, an electrical impulse triggered when the charge rises to threshold (about -55mV) and travels down the axon.

Is resting potential the same as hyperpolarization?

No. Hyperpolarization is a brief dip below resting potential that happens right after a neuron fires. It makes the neuron harder to fire during the refractory period until the charge settles back to its normal resting level.

Do I need to know the sodium-potassium pump for the AP Psych exam?

No. The CED explicitly says the sodium-potassium pump is outside the scope of the AP Psychology Exam. You only need to know what resting potential is and how it fits with depolarization, threshold, the action potential, and the refractory period.