The Physiology of the Nervous System Part 3

Hello. This is our third video focusing on the nervous system’s physiology, primarily giving a quick review of the sympathetic and parasympathetic nervous systems.

Sympathetic Nervous System (SNS)

The sympathetic nervous system mainly controls the fight and flight response, which, in layman’s terms, would be the system responsible for responding during a stressful situation. And the two main organs that are involved in the sympathetic nervous system are the heart and lungs.

On the other side of the spectrum, when the sympathetic nervous system is turned off, the parasympathetic nervous system is turned on. So, the SNS and PNS have a teeter-totter- like communication.

Parasympathetic Nervous System (PNS)

You can think of the parasympathetic nervous system as the opposite of the sympathetic nervous system. The PNS is also known as the rest and digest system, essentially in charge of the gastrointestinal system and urinary system.

Anticholinergic vs. Cholinergic

If the sympathetic nervous system is activated, its anticholinergic properties are also engaged. Meaning, the client’s heart will race, and fast, deep breathing will follow. Anticholinergic is also known as sympathomimetic drugs that affect sight, pee, and poop in a way that they won’t work while the SNS is at peak.

Now, if the parasympathetic nervous system is triggered, the body will experience cholinergic effects which are opposite of what one feels when the SNS is turned on; the client will have normal eyesight, digestion, salivation, urination, and excretion.


Let’s discuss the different drugs under anticholinergic and cholinergic classifications.


Anticholinergic drugs are mostly:

  • Beta-1 (affects the heart)
  • Beta-2 (affects the lungs)

To easily memorize which beta works for either the lungs or heart, remember: beta-1 is for the heart because humans only have one heart, while beta-2 is for the lungs because there are two lungs.

Beta-1 vs. Beta-2

Beta-1 agonist causes cardiac stimulation which results in increased heart rate, contractility, and relaxation; these drugs shunts blood from the rest of the body to the heart and lungs to better supply these organs with oxygen, to sustain the fight and flight response during stressful situations. Epinephrine and dopamine are well-known beta-1 drugs. Caffeine is also a potent beta-1 adrenergic agonist.

On the other hand, beta-2 agonist causes lung dilation; the bronchial tubes and bronchioles will expand, resulting in better breathing. Medications ending in “-terol,” like Albuterol, the rescue inhaler, is a typical example of a beta-2 drug.


Cholinergic drugs also known as anti-adrenergic drugs are those that block the receptors, mainly the beta-1 and beta-2 receptors.  Cholinergic medications cause contraction of the smooth muscles, blood vessels dilation, increased secretions, decreased heart rate.

Beta-blockers affect both the lungs and heart; which is why it is essential that blood pressure and respiration are monitored if the client is receiving this kind of treatment. Assessment is important to prevent lung collapse and other side effects.

So, that’s it for our nervous system review part three. Hopefully, this lecture has shed light on this confusing topic about the sympathetic and parasympathetic nervous system and the drugs involved.

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Cholinergic and Anticholinergic Pharmacology Made Easy

Today, we’ll be focusing our attention on anticholinergic bronchodilators.

In the simplest sense, you anticholinergic bronchodilators are your drugs that have the capacity to turn off the system in your body that causes the fight and flight reaction.

To explain further…

Sympathetic versus Parasympathetic

So, there are two systems involved – the sympathetic nervous system and the parasympathetic nervous system. How do you distinguish one from the other?

  • Sympathetic nervous system (SNS) – fight and flight
  • Parasympathetic nervous system (PNS) – rest and digest

When trying to differentiate one from the other, there are a couple of questions that you need to ask:

  1. Where is the blood going?
  2. Is it headed towards your fight and flight organs or towards your digest and rest organs?
  3. What are your fight and flight organs?
  4. What are your digest and rest organs?

Your fight and flight organs are:

  1. Heart
  2. Lungs
  3. Brain

Your digest and rest organs are:

  1. Gastrointestinal (GI) Tract
  2. Kidneys
  3. Muscles
  4. Other organs

The teeter-totter figure

To make your memorization easier, imagine a teeter-totter.

On the left side, is your sympathetic nervous system (SNS), and on the right side is your parasympathetic nervous system (PNS) or the parasympathomimetics nervous system. Below your SNS, write down the organs responsible for the fight and flight reaction which is your heart, lungs, and brain. Then below the PNS, write down the organs responsible for the digest and rest reaction.

Anticholinergic versus Cholinergic

After identifying what your SNS and PNS are, we now have to relate them to your cholinergic and anticholinergic drugs.

How does one distinguish anticholinergic from cholinergic drugs?

Sympathomimetic reactions (fight and flight) – Anticholinergic drugs

The mechanism of anticholinergic drugs is to direct blood to your heart, lungs, and brain by inhibiting the parasympathetic nervous system. When the signal going to the PNS is blocked or disrupted, the involuntary functions like mucus secretion, salivation, urination, and digestion is decreased significantly.

Examples: Atropine, Epinephrine

Parasympathetic nervous system (rest and digest) – Cholinergic drugs

On the other hand, cholinergic drugs are basically the opposite of the SNS. Because with cholinergic drugs, there is an increase in involuntary functions which basically means that there is saliva production, urination, and mucus secretion.

An instructor of Mike’s once shared a very useful tip when remembering cholinergic and anticholinergic drugs. Just remember the 3 S’s:

  • See
  • Spit
  • Shit (excrete)

Simply put it this way:

Anticholinergics – can’t see, can’t spit, can’t shit

Cholinergics – can see, can spit, can shit

Easy enough?

Cholinergic agents allow you to see due to the production of fluid that moisturizes the eyes and you can salivate because of the production of mucus. You can also urinate and defecate.

Anticholinergic agents decrease all the activities mentioned above. Instead, you will increase the client’s heart rate and perfusion to the lungs and brain.

So just remember…

Administering drugs with SNS and PNS effects will directly influence where the blood will be heavily distributed for the sake of treating a number of conditions. If you turn one off, the other is turned on. Don’t forget the teeter-totter figure.