Autonomic Nervous System section 2 unit 2 PT.1

Parasympathetic Nervous System (PNS)

meaning

Cholinergic- "Rest and Digest" 😌🍽

Think of the parasympathetic nervous system as your body's relaxation mode . It turns on when you're safe, calm, eating, or sleeping.

1. Restoration of Energy Stores

What it means:
Your body is saving and rebuilding energy.

✅ Slows the heart down
✅ Uses less energy
✅ Stores nutrients from food

Easy memory:
"Recharge your battery." 🔋

Parasympathetic Nervous System

what it does

2. Balance

What it means:
Keeps the body calm and steady after stress.

Example:

• After running → heart rate slows

• After being scared → body calms down

Easy memory:
"Brings the body back to normal." ⚖

3. Stimulates One Specific Body Part/System

Unlike the sympathetic system ("fight or flight"), which affects many organs at once, the parasympathetic system usually works on one organ at a time .

Example:

• Digesting food → mainly digestive system

• Making tears → mainly eyes

Easy memory:
"Targeted action, not whole-body action." 🎯

Parasympathetic Nervous System

4. Neurotransmitter (NT) = Acetylcholine (ACh)

A neurotransmitter is a chemical messenger that carries signals between nerves.

In the parasympathetic system:

Preganglionic neuron → releases ACh

⬇

Ganglion (relay station)

⬇

Postganglionic neuron → releases ACh

⬇

Target organ

Simple Flow:

🧠 Brain/Spinal Cord
⬇ ACh
🔄 Ganglion
⬇ ACh
❤ Stomach, lungs, eyes, etc.

Parasympathetic = ACh → ACh

Parasympathetic Nervous System

what it does side by side

Organ	Effect
Eyes 👀	Pupils constrict
Heart ❤	Heart rate decreases
Lungs 🫁	Airways constrict slightly
Stomach 🍔	Digestion increases
Salivary glands 🤤	More saliva
Bladder 🚽	Helps you urinate

Parasympathetic = Rest, Digest, ACh

R = Rest
D = Digest
ACh = Acetylcholine at both ganglia and postganglionic endings

Think:

"When I'm relaxing after a meal, my parasympathetic system uses ACh to help me rest and digest." 😌🍽🔋

Parasympathetic Nervous System

Vagus Nerve (Cranial Nerve X)

What is the vagus nerve?

The Vagus Nerve is the 10th cranial nerve (CN X) .

It is the body's main parasympathetic nerve ("Rest and Digest" nerve).

Easy Memory:

👉 Vagus = Vacation nerve 😌

When the vagus nerve is active, your body is in relaxation mode .

Where Does It Go?

The vagus nerve travels from the brain to many organs:

🗣 Larynx = voice box (helps with speaking)

👄 Pharynx = throat (helps with swallowing)

❤ Heart

🫁 Lungs

🩸 Blood vessels

🍔 Digestive organs (stomach, intestines)

Think:

"The vagus nerve visits the throat, heart, lungs, and stomach."

Vagus Nerve

What Does It Do?

• Parasympathetic responses

• slows heart

• bronchoconstriction-The vagus nerve makes them slightly narrower.

• increases GI activity- time to digest food

• decreases blood pressure- HR decreases BP decrease

Vagus Nerve

Other Jobs of the Vagus Nerve

🤢 Gag Reflex

Helps trigger the gag reflex when something touches the back of your throat.

🗣 Speaking

Controls muscles of the voice box.

Without it, speaking becomes difficult.

😓 Sweating

Helps regulate some body functions involved with sweating.

Vagus Nerve

Vasovagal Response

Sudden stimulation → drop in HR and BP, “vasovagal,” can result in syncope

Sometimes the vagus nerve gets stimulated too much.

Examples:

• Seeing blood

• Fear

• Pain

• Standing too long

The vagus nerve suddenly says:

"Slow everything down!"

What Happens?

❤ Heart rate drops

🩸 Blood pressure drops

⬇

🧠 Less blood reaches the brain

⬇

😵 Person faints

This is called:

Vasovagal Syncope

• Vaso = blood vessels

• Vagal = vagus nerve

• Syncope = fainting

vagus nerve side by side

Vagus Nerve Effect	What Happens?
❤ Heart	Slows heart rate
🩸 Blood Pressure	Decreases BP
🫁 Lungs	Bronchoconstriction
🍔 Digestive System	Increases digestion
🤢 Throat	Gag reflex
🗣 Voice Box	Speaking
😵 Too Much Stimulation	Vasovagal syncope (fainting)

Vagus nerve = Rest and Digest nerve that slows the heart, lowers blood pressure, helps digestion, and can cause fainting if overstimulated. 😌❤🍔😵

Parasympathetic Effects

Parasympathetic Nervous System Effects

"Rest and Digest" 😌🍔

Its job is to slow things down, relax the body, digest food, and help you pee and poop.

Neurotransmitter:

🧪 ACh (Acetylcholine)

• Released by parasympathetic nerves

• Also called cholinergic

• ACH is released (cholinergic)

Easy Memory:
👉 Parasympathetic = ACh = Rest and Digest

❤ Heart Effects Decreased Heart Rate

Heart beats slower.

Why?
Your body is resting and doesn't need to pump blood as fast.

Decreased Conduction

Electrical signals move slower through the heart.

Decreased Contractility

The heart squeezes less forcefully.

Easy Memory:
❤ Slow, Slow, Slow

• Slower heart rate

• Slower electrical signals

• Weaker contractions

Parasympathetic Nervous System Effects

2

👀 Miosis What is Miosis?

Pupil constriction (pupils get smaller).

Example: When relaxing or in bright light.

👀 Miosis = Mini pupils

🫁 Bronchoconstriction What's happening?

Airways become a little narrower.

Why? The body is resting, not running from danger.

Easy Memory:
🫁 Resting lungs = smaller airways

🍔 Increased Digestion

The stomach and intestines become more active.

✅ More movement of food

✅ Better digestion

time to digest lunch

🚽Urinary Bladder Contraction - SQUEEZE

🚽 Urinary Sphincter Relaxation- 🚽 Door opens

🚽 Increased Urination

Bladder squeezes + sphincter relaxes= More urination

💩 Increased Defecation

"Go to the bathroom"

Parasympathetic Nervous System Effects

VESSEL

Most arteries are NOT controlled by the parasympathetic system.

The parasympathetic system mainly affects:

❤ Heart

🫁 Lungs

🍔 Digestive system

🚽 Bladder

Not most arteries.

Parasympathetic Nervous System Effects

SIDE BY SIDE

Body Part	Parasympathetic Effect
❤ Heart	Slower heart rate
👀 Eyes	Miosis (small pupils)
🫁 Lungs	Bronchoconstriction
🍔 Stomach/Intestines	Increased digestion
🚽 Bladder	Contracts
🚽 Urinary Sphincter	Relaxes
🚽 Urination	Increases
💩 Defecation	Increases

Parasympathetic = "SLUDD"

S = Small pupils (Miosis) 👀

L = Lower heart rate ❤

U = Urination

D = Digestion 🍔

D = Defecation 💩

Think:

"Rest, digest, pee, and poop." 😌🍔🚽💩

3 Types of Cholinergic Receptors (Easy Version)

First, What is a Cholinergic Receptor?

A cholinergic receptor is a receptor that responds to Acetylcholine (ACh) .

Think of it like:

🧪 ACh = Key
🔒 Receiver = Lock

When ACh fits into the receptor, something happens.

Important:

✅ All 3 receptors are activated by ACh

muscarinic: 

nicotinic 1 (Nn): 

nicotinic 2 (Nm): 

3 Types of Cholinergic Receptors (Easy Version)

1. Muscarinic Receptors (M)

Where are they?

Found on:

❤ Heart

🫁 Smooth muscle (lungs, intestines, bladder)

🧴 Glands (salivary glands, digestive glands)

At parasympathetic postganglionic nerve endings

What happens when stimulated?

❤ Heart rate decreases

🫁 Bronchoconstriction

🍔 Digestion increases

🧃 Digestive secretions increase

🚽 Urination increases

👀 Pupils constrict (miosis)

M = Maintenance Mode

When you're resting

❤ Heart slows

🍔 Digest food

🚽 Pee

👀 Small pupils

Everything is Rest and Digest .

3 Types of Cholinergic Receptors (Easy Version)

2. Nicotinic 1 (Nn)

Where are they?

At the ganglia of:

✅ Sympathetic nervous system

✅ Parasympathetic nervous system

Think of them as the relay station receivers .

What do they do?

They help pass the message from:

Preganglionic neuron

⬇

Ganglion

⬇

Postganglionic neuron

Easy Memory: Nn = Nerve to Nerve

🧠 Nerve → Nerve

They help nerves talk to other nerves.

3. Nicotinic 2 (Nm)

3 Types of Cholinergic Receptors

Where are they?

At the neuromuscular junction

This is where:

🧠 Nerve meets 💪 Skeletal muscle

Part of the Somatic Nervous System (voluntary movement).

What happens when stimulated?

💪 Skeletal muscle contracts

Examples:

✅ Walking

✅ Writing

✅ Smiling

✅ Lifting weights

Nm = Nerve to Muscle

🧠 Nerve → Muscle

ACh tells the muscle:

"Contract!"

💪 Muscle contracts.

3 Types of Cholinergic Receptors

side by side

Receptor	Location	Easy Job
Muscarinic (M)	Heart, smooth muscle, glands	Rest and Digest
Nicotinic 1 (Nn)	Autonomic ganglia	Nerve → Nerve
Nicotinic 2 (Nm)	Neuromuscular junction	Nerve → Muscle

M = Muscarinic = Maintenance Mode 😌

• ❤ Slow heart

• 🍔 Digest food

• 🚽 Urinate

• 👀 Small pupils

Nn nicotinic 1 = Nicotinic Neuron 🧠➡🧠

• Nerve talks to nerve

Nm nicotinic 2 = Nicotinic Muscle 🧠➡💪

• Nerve tells muscle to contract

ACh activates all cholinergic receptors:

• Muscarinic = Rest and Digest

• Nn = Nerve to Nerve

• Nm = Nerve to Muscle 💪

Neurotransmission of Parasympathetic Nerves

Step 1: First Neuron (Preganglionic Neuron)

🧠 Brain or spinal cord

⬇

🏃 Preganglionic neuron

⬇

🔄 Ganglion (relay station)

At the ganglion, the first neuron releases:

🧪 Acetylcholine (ACh)

This ACh tells the second neuron:

"Okay, your turn! Carry the message."

Neurotransmission of Parasympathetic Nerves

Step 2: Second Neuron (Postganglionic Neuron)

🔄 Ganglion

⬇

🏃 Postganglionic neuron

⬇

❤ Heart, 🍔 stomach, 🫁 lungs, 🚽 bladder

At the organ, the second neuron ALSO releases:

🧪 Acetylcholine (ACh)

This ACh tells the organ what to do.

Examples:

❤ Heart → slow down

🍔 Stomach → digest food

🚽 Bladder → urinate

👀 Eyes → pupils constrict

BRAIN

↓

Preganglionic Neuron

↓ releases ACh

GANGLION

↓

Postganglionic Neuron

↓ releases ACh

TARGET ORGAN

What Your Notes Mean "NT released at ganglia is ACh"

Means:

The preganglionic neuron releases ACh at the ganglion.

🧠 → ACh → Ganglion

"NT released at postganglionic nerve endings is ACh"

Means:

The postganglionic neuron releases ACh onto the organ.

Ganglion → ACh → ❤🍔🫁🚽

Parasympathetic = ACh → ACh

🧠 → ACh → Ganglion

Ganglion → ACh → Organ

Both neurons use Acetylcholine .

Parasympathetic Nerves steps

Parasympathetic Nervous System

✅ Long preganglionic neuron

✅ ACh released at ganglion

✅ Nn receptor at ganglion

✅ ACh released at organ

✅ Muscarinic receptor on organ

BRAIN

↓

Long Preganglionic Neuron

↓ releases ACh

Nn Receptor (Ganglion)

↓

Short Postganglionic Neuron

↓ releases ACh

Muscarinic Receptor (Organ)

↓

Rest and Digest Effect

Quick Memory Trick

"ACh → Nn → ACh → Muscarinic"

🧠 → ACh → Nn

⬇

ACh → Muscarinic

⬇

😌 Rest and Digest (slow heart, digest food, pee, poop)

Step 7: Muscarinic Receptor on the Organ

The organ has:

🔵 Muscarinic receptors

Your notes say:

Muscarinic receptor at postganglionic nerve endings

This means the target organ (heart, lungs, stomach, bladder, etc.) has muscarinic receptors that receive the ACh.

Easy Memory

Muscarinic = Rest and Digest receptor

When ACh binds to muscarinic receptors:

❤ Heart slows

🍔 Digestion increases

🚽 Urination increases

👀 Pupils constrict

🫁 Bronchoconstriction

ANS Drug Effects

Parasympathomimetic vs

Parasympatholytic

Parasympathomimetic	Parasympatholytic
Mimics ACh	Blocks ACh
Cholinergic agonist	Cholinergic antagonist
Rest and Digest ON	Rest and Digest OFF
↓ Heart rate	↑ Heart rate
Small pupils	Large pupils
↑ Digestion	↓ Digestion
↑ Urination	↓ Urination

MIMETIC = MIMICS 😌

Parasympathomimetic
= Acts like ACh
= Rest and Digest

---

LYTIC = BLOCKS 🚫

Parasympatholytic
= Blocks ACh
= Opposite of Rest and Digest

---

One-Line Memory

✅ Parasympathomimetic = "Do more Rest and Digest.

🚫 Parasympatholytic = "Block Rest and Digest."

Cholinergics/Parasympathomimetics 

side by side

Problem	What the Drug Does
👀 Large pupil	Constricts pupil (miosis)
👀 High eye pressure	Lowers eye pressure
🚽 Can't pee	Helps bladder contract
💩 Constipation	Increases intestinal movement

Direct Cholinergic Agonists = "Fake ACh"

They stimulate muscarinic receptors and cause:

👀 Miosis

👀 ↓ Eye pressure

🚽 Urination

💩 More bowel movement

Think:

"See, Pee, and Poop"

👀 See (glaucoma)

🚽 Pee (urinary retention)

💩 Poop (intestinal stasis)

That's the easiest way to remember what these drugs do. 😊

Cholinergics/Parasympathomimetics 

First, what are they?

These drugs act like Acetylcholine (ACh) .MIMICS

They turn on the parasympathetic nervous system ("Rest and Digest").

Easy Memory:

🧪 Drug = Fake ACh

The drug claims to be ACh and activates parasympathetic receptors.

Directly stimulate/bind to muscarinic receptors

What does that mean?

Normally:

ACh ➡ Muscarinic receptor ➡ Effect

With these drugs:

💊 Drug ➡ Muscarinic receptor ➡ Same effect

The drug acts like ACh.

Direct-Acting Cholinergic Agonists

acetylcholine

pilocarpine (Pilocar®)

bethanechol

Direct-Acting Cholinergic Agonists = "Fake ACh"

💊 Drug pretends to be ACh

⬇

🔒 Binds directly to Muscarinic receiver

⬇

😌 Rest and Digest turns ON

Think:

👀 Small pupils

🚽 Pee

💩 Poop

❤ Slow heart

That's the main idea of ​​this entire diagram. 🎯

Normal Pathway

vs

Direct-Acting Cholinergic Agonist Pathway

Normal Pathway

Nerve makes ACh

↓

ACh released

↓

Muscarinic receptor

↓

Rest and Digest effects

↓

ACh destroyed by acetylcholinesterase

Direct-Acting Cholinergic Agonist Pathway

Drug (Bethanechol)

↓

Directly binds Muscarinic receptor

↓

Acts like ACh

↓

Rest and Digest effects

Normal: ACh → Muscarinic receptor → Effect

Drug: Drug → Muscarinic receptor → Same effect

Why Do Indirect-Acting Drugs Help?

They increase ACh.

More ACh means a better chance of stimulating the remaining receptors.

inhibit acetylcholinesterase, the enzyme that destroys ACH in the synapse

increases ACH

Result:

💪 Improved muscle strength

Antidote for Cholinergic Poisoning

Too much ACh can be dangerous.

Symptoms may include:

🚽 Too much urination

💩 Diarrhea

🤤 Excessive saliva

❤ Very slow heart rate

Antidote = Atropine

Atropine blocks muscarinic receptors.

***Antidote for cholinergic poisoning - atropine

Think:

Too much ACh

↓

Give atropine

↓

Blocks ACh effects

Indirect –Acting Cholinergic Agonists

Term	Easy Meaning
Acetylcholinesterase	Enzyme that destroys ACh ✂
Indirect-acting agonist	Blocks ACh destruction
Result	More ACh
Urinary retention	Helps patient pee 🚽
Ileus	Helps intestines move 💩
Myasthenia gravis	Helps weak muscles 💪
Atropine	Antidote for too much ACh

Direct-Acting Drug

💊 Acts like ACh

Indirect-Acting Drug

💊 Protects ACh

Myasthenia Gravis

💪 Weak muscles because the body attacks Nm receptors

Atropine

🚫 Blocks ACh when there is too much

👉 Indirect-acting cholinergic agonists block acetylcholinesterase, causing more ACh to stay in the synapse and produce stronger parasympathetic effects.

 Indirect-Acting Cholinergic Agonists

neostigmine - reverses actions of rocuronium bromide which causes respiratory paralysis from anesthesia

What Do Indirect-Acting Drugs Do?

 Indirect-Acting Cholinergic Agonists

They block acetylcholinesterase .

SW:

🚫 Acetylcholinesterase blocked

⬇

ACh is NOT destroyed

⬇

More ACh stays in the synapse

⬇

Stronger parasympathetic effects

Indirect = Protects ACh

Instead of acting like ACh, it keeps ACh alive longer.