( 4b ) Parasympathetic Nervous System

remember:

Parasympathetic is a subgroup of

Autonomic Nervous System

so it’ll have the varicosities at the postganglionic fiber

Anatomy wise

Parasympathetic Nervous System is

Craniosacral

Craniosacral means

The parasympathic neurons are coming from the

• Cranial Region

  OR

• Sacral Region

Cranial

refers to

Brain

Sacral

refers to

Spinal Cord

( lower area )

In this pic

→ we can see that cranial nerves come out the

Brain

What’s the cranial nerve we need to know?

#10 Vagus Nerve ( X )

Does the Vagus Nerve

have parasympathetic neurons or sympathetic neurons?

Parasympathetic neuron!

( remember nerves are bundles of many neuron’s axons )

What does it affect?

Abdominal ( tummy )

Thoracic ( chest )

• Breathing

• Heart rate

• Digestive Tract

• etc.

Parasympathetic’s

preganglionic ( first ) neuron

long or short?

quite LONG

The ganglion ( aka terminal ganglion )

is most often located

IN the final effector organ

examples:

• it’s IN our heart

• it’s IN our smooth muscle

• it’s IN our glands

Notice

The ganglions ( black dots )

are IN the effector organs!

So how far does the

Preganglionic ( first ) neuron

have to go?

ALL THE WAY to the ORGAN

= why it’s so long!

since we’re already in the organ:

Is the postganglionic ( second ) neuron

long or short?

Short

So what’s the usual length of the Parasympathetic Nervous System’s

Preganglionic vs. Postganglionic neurons?

Preganglionic : Long

Postganglionic: Short

What else can we call these neurons?

Cholinergic Neurons

Cholinergic

means

Acetycholine ( Ach )

What does the preganglionic ( first ) neuron release as a neurotransmitter?

Acetycholine ( Ach )

What does the postganglionic ( second ) neuron release as a neurotransmitter?

Acetycholine ( Ach )

Saying

“Both of these neurons are Cholinergic”

means

they release Acetycholine ( Ach )

So what type of receptor would the receiving cell have?

Cholinergic Receptors

What do Cholinergic Receptors do?

recieve Acetycholine ( Ach )

form the previous neuron

What 2 Proteins

are Cholinergic Receptors ?

• Nicotinic

• Muscarinic

What’s their job (designed to do ) ?

Bind to Acetylcholine ( Ach )

How are they different?

Beside from binding to Acetylcholine ( Ach )

Nicotinic receptors ALSO binds to

nicotine

( like the cigarette one - plant based and NOT in human body )

So if nicotine enters the body

where will it bind to?

The EXACT SAME nicotinic receptors that Acetylcholine ( Ach ) binds to !!

Beside from binding to Acetylcholine ( Ach )

Muscarinic receptors ALSO binds to

muscarine

• a toxin from certain speicies of poisonous mushrooms

Review:

The preganglionic neuron is cholinergic → releases acetylcholine

So that means the cell bodies and dendrites of the POSTganglionic cell must have

Cholinergic Receptors

What Cholinergic Receptors

is the postganglionic cell’s dendrites and cell bodies?

Nicotinic receptor

So this ganglion area has

Nicotinic receptors

→ binds to acetylcholine ( Ach )

BUT also nicotine if it’s present

What other place has Nicotinic Receptors?

Neuromuscular Junction !!

( communication point between motor neuron and skeletal muscle cell )

There’s Acetylcholine released

So the Motor End Elate has

Cholinergic Receptors

( specifically Nicotinic !! )

Review Question:

What type of CHANNEL is the

nicotinic acetylcholine ( Ach ) receptor in the neuromuscular junction?

Monovalent Cation Channel

→ Na⁺ AND K⁺ goes through! ( but Na⁺ is faster )

= depolarization → EPP → action potential!

What’s OTHER place that has monovalent cation channels?

Excitatory Synapse !!

• On dendrites and cell bodies

( part of past graded potential lectures )

Overview of Parasympathetic Nervous System so far":

1. First neuron is cholinergic

   → releases acetylcholine

2. Acetylcholine binds to nicotinic receptor

   → this receptor is a monovalent cation channel

= The second neuron gets excited !!

3. The second neuron is ALSO cholinergic

   → also releases acetylcholine

BUT it releases acetylcholine from a DIFFERENT area

The second postganglionic fiber releases acetylcholine from

Varicosities !!

Varicosities go ALL OVER our

• Smooth muscle

• Cardiac muscle

• Glands

= effector organs

What type of Cholinergic Receptors will these effector organ’s tissues have?

Muscarinic receptors

( the OTHER type of acetylcholine receptor )

How teacher remembers which one is which

It’s ALWAYS gonna be a nicotinic receptor

EXCEPT for this one case:

When it’s the parasympathetic nervous system

RIGHT ON the

• Smooth Muscle

• Cardiac Muscle

• Glands

What will ALWAYS be ON these effector organs?

Muscarinic receptors

BESIDES from them

Every OTHER time we mention acetylcholine receptors it’ll always be

Nicotinic

ex. in the neuromuscular junction it’s nicotinic

ex. The ganglion has nicotinic receptors

the ONE EXCEPTION is when it’s ON

• Smooth Muscle

• Cardiac Muscle

• Gland

it’ll be

Muscarinic receptors

Muscarinic receptors are

G-Protein Coupled

• different receptor unlike the nicotinic monovalent cation channel

Pic shows : Varicosity

Remember postganglionic neurons have varicosities

1. Acetylcholine will be released all over the tissue

And this tissue has what receptors on it?

Muscarinic receptors

2. Acetylcholine binds to muscarinic receptors

and that activates the

G-Protien

What will the G-Protien activate?

Depends on where it is!

→ Activates different effects for each cell types!!

• heart

• smooth muscle

• digestive tracts

• glands

• etc.

Overall

Acetylcholine released from both neurons

• In First Synapse → it binds to nicotinic receptors

  • Excites the second neuron

    → second neuron releases acetylcholine onto tissue

  • Tissue has muscarinic receptors

What type of response will come out from these tissues?

Parasympathetic Response