The Physiology of the Nervous System Part 3

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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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