---
title: "EPSP in Intro to Psychology"
description: "EPSP is an excitatory postsynaptic potential that depolarizes a neuron and brings it closer to firing an action potential in Intro to Psychology."
canonical: "https://fiveable.me/intro-psychology/key-terms/epsp"
type: "key-term"
subject: "Intro to Psychology"
unit: "Unit 3"
---

# EPSP in Intro to Psychology

## Definition

EPSP means excitatory postsynaptic potential. In Intro to Psychology, it is the depolarizing change in a neuron that makes firing an action potential more likely.

## What It Is

An EPSP in Intro to Psychology is the small electrical change that makes a postsynaptic neuron more likely to fire. EPSP stands for excitatory postsynaptic potential, and it happens when an excitatory neurotransmitter binds to receptors on the postsynaptic membrane and opens channels that move the membrane toward threshold.

The simplest way to picture it is this: the neuron starts at a resting state, then a chemical signal arrives at the dendrite or cell body, and the inside of the neuron becomes a little less negative. That shift is called depolarization. By itself, one EPSP usually is not enough to trigger an action potential, but it pushes the neuron closer to the point where it can fire.

This is where the word postsynaptic matters. The EPSP happens in the neuron receiving the message, not the neuron releasing it. The presynaptic neuron sends neurotransmitters from its axon terminals across the synapse, and the postsynaptic membrane receives them through neurotransmitter receptors. In many intro psych examples, glutamate is the excitatory neurotransmitter people talk about most often.

EPSPs are graded, not all-or-nothing. A stronger signal can create a larger depolarization, and multiple EPSPs can add together if they happen close enough in time or at nearby spots on the neuron. That summation is how a neuron decides whether to cross threshold at the axon hillock and produce an action potential.

A good way to remember it is that an EPSP is like a push toward firing, not the firing itself. If the neuron also receives inhibitory signals at the same time, those can cancel out some of the depolarization. So when you see EPSP in a question, think about a neuron receiving an excitatory message, moving closer to threshold, and possibly combining with other signals before it fires.

## Why It Matters

EPSP shows up whenever Intro to Psychology shifts from naming parts of neurons to explaining how they actually communicate. Without EPSPs, you are just memorizing anatomy. With EPSPs, you can trace how a chemical message becomes an electrical decision in the receiving neuron.

That matters for questions about behavior, sensation, learning, and brain function because neurons do not fire randomly. They sum inputs, compare excitatory and inhibitory signals, and only then decide whether to send an action potential down the axon. EPSPs are part of that decision-making process.

It also helps with signal-flow questions. If a prompt describes neurotransmitters released from axon terminals, binding to receptors, and a membrane becoming more positive, you should be able to identify the event as an EPSP rather than a full action potential. That distinction shows you understand the sequence of communication at the synapse.

EPSPs also connect to common unit ideas like summation and threshold. A neuron can receive several small excitatory inputs that individually do nothing, but together they can bring the membrane to firing level. That is a big reason the nervous system can be selective instead of reacting to every tiny signal.

## Connections

### [Action Potential](/intro-psychology/key-terms/action-potential)

An EPSP is one of the events that can lead to an action potential, but it is not the same thing. EPSPs are small graded depolarizations in the postsynaptic neuron, while an action potential is the full electrical spike that travels down the axon once threshold is reached. If a question asks what happens next after enough EPSPs add up, action potential is usually the answer.

### Neurotransmitter

EPSPs are caused by excitatory neurotransmitters binding to receptors on the postsynaptic membrane. That means you need the chemical messenger first before you get the electrical change. In intro psych questions, neurotransmitter names can clue you in to whether the signal is excitatory or inhibitory, especially when the prompt mentions synaptic communication.

### [Neurotransmitter Receptors](/intro-psychology/key-terms/neurotransmitter-receptors)

Receptors on the postsynaptic membrane are what let the neuron detect the neurotransmitter and respond with an EPSP. If the receptor does not bind the message, the excitatory effect does not happen. This connection comes up in questions about how specificity works at the synapse, because only neurons with the right receptors react in the right way.

### [Neurotransmitter Reuptake](/intro-psychology/key-terms/neurotransmitter-reuptake)

Reuptake ends the signal by pulling neurotransmitters back into the presynaptic neuron, which can reduce how long an EPSP lasts. That is why reuptake changes signal strength and timing. If a question asks why a postsynaptic response is shorter or weaker, reuptake is one possible reason.

## On the AP Exam

A quiz question might describe glutamate binding to receptors and ask what happens to the postsynaptic neuron. You would identify the change as an EPSP because the membrane is depolarizing and moving closer to threshold. In a diagram question, look for the postsynaptic side of the synapse and a small shift toward a less negative membrane potential.

You may also see EPSP in short-answer prompts about summation. The move is to explain that several EPSPs can add together over time or from different synapses, and that this increases the chance of an action potential. If the item includes both excitatory and inhibitory signals, explain whether the neuron reaches threshold or gets held back by IPSPs.

## EPSP vs IPSP

EPSPs and IPSPs are easy to mix up because both happen on the postsynaptic neuron after neurotransmitters bind to receptors. EPSPs are excitatory and depolarize the membrane, bringing it closer to threshold. IPSPs are inhibitory and make firing less likely by moving the membrane away from threshold or counteracting excitation.

## Key Takeaways

- An EPSP is a small depolarization in the postsynaptic neuron that makes firing an action potential more likely.
- It happens after an excitatory neurotransmitter binds to receptors on the postsynaptic membrane.
- EPSPs are graded, so several of them can add together and push the neuron to threshold.
- An EPSP is not the same as an action potential, which is the full signal that travels down the axon.
- If inhibitory signals are present too, they can reduce or cancel the effect of an EPSP.

## FAQs

### What is EPSP in Intro to Psychology?

EPSP stands for excitatory postsynaptic potential. In Intro to Psychology, it is the depolarizing change that happens in the receiving neuron after an excitatory neurotransmitter binds to its receptors. This makes the neuron more likely to reach threshold and fire an action potential.

### How is EPSP different from an action potential?

An EPSP is a small, graded change in membrane potential, while an action potential is the full electrical impulse that travels down the axon. EPSPs can add together and help the neuron reach threshold, but they do not themselves move the signal down the neuron. Once threshold is reached, the action potential takes over.

### How do EPSPs add up?

EPSPs can sum when they happen close together in time or at nearby places on the neuron. This means multiple excitatory inputs can combine into a larger depolarization. If the combined effect reaches threshold, the neuron fires an action potential.

### What neurotransmitter causes an EPSP?

A common example is glutamate, which is usually the main excitatory neurotransmitter discussed in intro psych. The exact neurotransmitter can vary by synapse, but the important part is that it binds to receptors and depolarizes the postsynaptic membrane. That excitatory effect is what makes it an EPSP.

## Related Study Guides

- [3.2 Cells of the Nervous System](/intro-psychology/unit-3/2-cells-nervous-system/study-guide/Dv5ov2Xy99aaOGdN)

## About This Document

Canonical Fiveable pages are available as Markdown at the same path plus `.md`.

- [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns
- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
- [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`)
- [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`)

## Structured Data

```json
{"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/intro-psychology/key-terms/epsp#resource","name":"EPSP in Intro to Psychology","url":"https://fiveable.me/intro-psychology/key-terms/epsp","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/intro-psychology/key-terms/epsp#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:22:12.771Z","isPartOf":{"@type":"Collection","name":"Intro to Psychology Key Terms","url":"https://fiveable.me/intro-psychology/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/intro-psychology/key-terms/epsp#term","name":"EPSP","description":"EPSP means excitatory postsynaptic potential. In Intro to Psychology, it is the depolarizing change in a neuron that makes firing an action potential more likely.","url":"https://fiveable.me/intro-psychology/key-terms/epsp","inDefinedTermSet":{"@type":"DefinedTermSet","name":"Intro to Psychology Key Terms","url":"https://fiveable.me/intro-psychology/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is EPSP in Intro to Psychology?","acceptedAnswer":{"@type":"Answer","text":"EPSP stands for excitatory postsynaptic potential. In Intro to Psychology, it is the depolarizing change that happens in the receiving neuron after an excitatory neurotransmitter binds to its receptors. This makes the neuron more likely to reach threshold and fire an action potential."}},{"@type":"Question","name":"How is EPSP different from an action potential?","acceptedAnswer":{"@type":"Answer","text":"An EPSP is a small, graded change in membrane potential, while an action potential is the full electrical impulse that travels down the axon. EPSPs can add together and help the neuron reach threshold, but they do not themselves move the signal down the neuron. Once threshold is reached, the action potential takes over."}},{"@type":"Question","name":"How do EPSPs add up?","acceptedAnswer":{"@type":"Answer","text":"EPSPs can sum when they happen close together in time or at nearby places on the neuron. This means multiple excitatory inputs can combine into a larger depolarization. If the combined effect reaches threshold, the neuron fires an action potential."}},{"@type":"Question","name":"What neurotransmitter causes an EPSP?","acceptedAnswer":{"@type":"Answer","text":"A common example is glutamate, which is usually the main excitatory neurotransmitter discussed in intro psych. The exact neurotransmitter can vary by synapse, but the important part is that it binds to receptors and depolarizes the postsynaptic membrane. That excitatory effect is what makes it an EPSP."}}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Intro to Psychology","item":"https://fiveable.me/intro-psychology"},{"@type":"ListItem","position":2,"name":"Key Terms","item":"https://fiveable.me/intro-psychology/key-terms"},{"@type":"ListItem","position":3,"name":"Unit 3","item":"https://fiveable.me/intro-psychology/unit-3"},{"@type":"ListItem","position":4,"name":"EPSP"}]}]}
```