---
title: "Parasympathetic Nervous System — AP Psych Definition"
description: "The parasympathetic nervous system is the \"rest and digest\" branch of the autonomic nervous system that calms your body after arousal, the opposite of the sympathetic system."
canonical: "https://fiveable.me/ap-psych-revised/key-terms/parasympathetic-nervous-system"
type: "key-term"
subject: "AP Psychology"
unit: "Unit 2"
---

# Parasympathetic Nervous System — AP Psych Definition

## Definition

The parasympathetic nervous system is the division of the autonomic nervous system that conserves energy and returns the body to a calm state after arousal, slowing heart rate, boosting digestion, and relaxing the body once a stressor passes.

## What It Is

The parasympathetic nervous system is one half of your **[autonomic nervous system](/ap-psych-revised/key-terms/autonomic-nervous-system "fv-autolink")**, the part of your nervous system that runs automatic stuff you don't consciously control, like your heartbeat and digestion. Its job is to calm you down. People nickname it the "rest and digest" system because it slows your heart rate, ramps up digestion and gland activity, and lets your body relax once a threat or stressor is gone.

Think of it as the brakes on your body's gas pedal. When something startles you, your [sympathetic nervous system](/ap-psych-revised/unit-1/2-overview-of-the-nervous-system/study-guide/4EFLv8T9ARX14r9M "fv-autolink") floors the gas (the "fight or flight" response). The parasympathetic system is what eases you back down to neutral afterward. The [neurotransmitter](/ap-psych-revised/unit-1/3-the-neuron-and-neural-firing/study-guide/AVvPhAH234j4u83J "fv-autolink") **acetylcholine (ACh)** does a lot of the messaging here, and the whole system works to keep your body in **homeostasis**, a stable internal balance.

## Why It Matters

This term lives in [Unit 2](/ap-psych-revised/unit-2 "fv-autolink"): Cognition, under topic 2.3, Overview of the Nervous System and the Neuron. You need it to map out how the nervous system is organized: central vs. peripheral, then somatic vs. autonomic, then sympathetic vs. parasympathetic within the autonomic branch. Knowing where the parasympathetic system sits in that tree is exactly the kind of structural knowledge MCQs love to test. It also connects to the bigger biological-bases-of-behavior theme, since understanding arousal and recovery helps explain [stress](/ap-psych-revised/key-terms/stress "fv-autolink"), emotion, and how the body responds during anxiety.

## Connections

### Sympathetic Nervous System (Unit 2)

These two are a matched pair. The sympathetic system arouses you (fight or flight), and the parasympathetic system brings you back down (rest and digest). They work in opposition to keep your body balanced.

### [Homeostasis (Unit 2)](/ap-psych-revised/key-terms/homeostasis)

The parasympathetic system is one of the body's main tools for restoring [homeostasis](/ap-psych-revised/key-terms/homeostasis "fv-autolink"). After arousal spikes your heart rate and breathing, it dials everything back to a stable resting state.

### Acetylcholine (ACh) (Unit 2)

[Acetylcholine](/ap-psych-revised/key-terms/acetylcholine "fv-autolink") is a key neurotransmitter the parasympathetic system uses to send its calming signals, so the term you learn for neuron communication shows up again in how this division actually functions.

### [Anxiety Disorders (Unit 5)](/ap-psych-revised/key-terms/anxiety-disorders)

When someone has an [anxiety](/ap-psych-revised/key-terms/anxiety "fv-autolink") disorder, the body can get stuck in a high-arousal sympathetic state. Treatments like relaxation training aim to engage the parasympathetic system to calm that overactivation.

## On the AP Exam

Expect this almost entirely on multiple-choice questions, usually as part of a "match the system to its function" setup. A classic stem asks which system returns the body to a calm, neutral state after a stressor goes away, and the answer is the parasympathetic system. Other stems test whether you can tell it apart from the sympathetic system (arousal) and the somatic system (voluntary skeletal muscle movement). Your job is to place it correctly in the nervous system hierarchy and pair it with the right physical effects: slower heart rate, more digestion, relaxation.

## Parasympathetic Nervous System vs Sympathetic Nervous System

Easy to mix up because they're both autonomic branches with similar names. The sympathetic system speeds you up for fight or flight (faster heart, dilated pupils, less digestion). The parasympathetic system slows you down for rest and digest (slower heart, more digestion). One arouses, one calms.

## Key Takeaways

- The parasympathetic nervous system is the "rest and digest" branch of the autonomic nervous system that calms the body after arousal.
- It does the opposite of the sympathetic nervous system, slowing heart rate and boosting digestion instead of revving you up.
- It helps restore homeostasis, returning the body to a stable, neutral resting state.
- Acetylcholine is the neurotransmitter that carries many of its calming signals.
- On the AP exam it shows up mostly in MCQs that ask you to match a nervous system division to its function.

## FAQs

### What does the parasympathetic nervous system do?

It calms your body down after arousal, slowing your heart rate, increasing digestion and gland activity, and helping you return to a relaxed resting state. That's why it's called the "rest and digest" system.

### Is the parasympathetic nervous system the same as the sympathetic nervous system?

No, they're opposites within the autonomic nervous system. The sympathetic system arouses you for fight or flight, while the parasympathetic system calms you back down once the threat is gone.

### How is the parasympathetic system different from the somatic nervous system?

The parasympathetic system is part of the autonomic nervous system and controls involuntary functions like heart rate and digestion. The somatic nervous system controls voluntary movements of your skeletal muscles, like raising your hand.

### Is the parasympathetic nervous system on the AP Psychology exam?

Yes. It's part of Unit 2, topic 2.3, and commonly appears in multiple-choice questions that ask you to identify which system returns the body to a calm state after a stressor passes.

### What neurotransmitter does the parasympathetic nervous system use?

Acetylcholine (ACh) is a key neurotransmitter involved in parasympathetic signaling, helping send the calming messages that slow the heart and support digestion.

## Related Study Guides

- [2.3 Overview of the Nervous System and the Neuron](/ap-psych-revised/unit-2/review/study-guide/6LIggXCKrR2TfcynGNdN)

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