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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Nervous System Anatomy and Physiology: Pharmacologic Reactions

This lecture is a continuation of our previous nervous system’s anatomy and physiology. In this piece, we will go through the involvement of sympathomimetic and parasympathomimetic drugs to the peripheral nervous system.

As a quick review, the nervous system is primarily composed of the following:

  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)

The peripheral nervous system is broken down into two parts, mainly:

  • Sympathetic nervous system
  • Parasympathetic nervous system

Sympathetic Nervous System

The sympathetic nervous system, also known as the fight or flight response, is related mainly to stress. This means that when stimuli trigger the sympathetic nervous system, the following occurrences, which are also signs of stress, are bound to happen:

  1. Increased heart rate
  2. Increased respiratory rate

Parasympathetic Nervous System

The parasympathetic nervous system, also known as the rest and digest response, is the opposite of the sympathetic nervous system. This is basically what happens when the body is not going into overdrive or utilizing the sympathetic nervous system.

The parasympathetic nervous system’s functions are:

  • Slows down the heart rate
  • Stimulates gastrointestinal activities
  • Relaxes the muscles of the urinary and excretory system

The Teeter-Totter Effect

Remember that the sympathetic nervous system and the parasympathetic nervous system are opposites, acting like a teeter-totter wherein, if one is turned on, the other is turned off automatically.

Sympathomimetic versus Parasympathomimetic

The sympathomimetic and parasympathomimetic drugs are like nicknames for the sympathetic and parasympathetic nervous system drugs, emulating their functions and actions inside the body.

The Sympathomimetic Drugs

Sympathomimetic drugs are sympathetic nervous system stimulants, jumpstarting the heart and lungs to increase their rates; thereby, boosting oxygen supply to numerous parts of the body and inducing better breathing.

Epinephrine is a typical example of a sympathomimetic drug. Epinephrine is adrenaline utilized in hospital settings, especially in emergency rooms.

The Parasympathomimetic Drugs

When the body is given parasympathomimetic drugs, other organs will be prioritized, and the following will happen:

  • Increased digestion
  • Increased mucus production
  • Increased blood flow to different organs

This means that there will be a cholinergic effect that can lead to better perfusion to the mucous membranes, gastrointestinal tract, and kidneys.

SNS and Adrenaline

Loading up adrenaline to a client will shunt blood to the two vital organs of the body – the heart and lungs. Blood pressure will shoot up, squeezing blood from the extremities to make sure that distribution will be focused on the system that matters most during distressing situations.

However, there are side effects that are expected to happen, namely:

  • Dry mouth
  • Constipation
  • Urinary retention
  • Confusion
  • Drowsiness

Hospital Scenario

A client who is in cardiac arrest comes into the emergency room. The health team is pumping the heart to perfuse the body. Are you going to give a parasympathomimetic or sympathomimetic drug?

To sustain life, the heart and lungs need to have adequate perfusion. Therefore, epinephrine and dopamine have to be given to raise the blood pressure and pulse, and shunt the required blood to the heart and lungs.

In our next discussion, we’ll be talking about agonist, adrenergic agonist, and antagonists.

Quick and Simple Nervous System Physiology

Hello. Let’s talk about the nervous system.

The nervous system is fundamentally broken up into two categories:

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)

Under the peripheral nervous system is the sympathetic and parasympathetic nervous system.

So, we’ll be briefly discussing these systems and also focus on the drugs that mainly affects how they function.

The Nervous System

As previously stated, the nervous system is composed of the central nervous system and the peripheral nervous system.

The central nervous system is composed mainly of the spinal cord and the brain. The CNS makes all the automatic responses of the body. On the other hand, the peripheral nervous system has more influence when it comes to the primary drugs that are administered to the body in terms of therapeutic response.

The sympathetic nervous system and parasympathetic nervous system act like a teeter-totter; meaning, if one is on, then the other one is off, and vice versa. So, this is what determines the drugs administered inside the hospital.

The Sympathetic Nervous System (SNS)

The sympathetic nervous system is referred to as the fight or flight response.

To easily remember this system, you can think about a bear chasing you and thinking, “Oh, snap!” That’s your sympathetic nervous system working because your body is immediately responding to the bear’s presence.

Now, whether you choose to run away from the bear or stay to fight the bear, your sympathetic nervous system is mainly working. But what are the main organs that comprise the SNS? The answer is your lungs and your heart. If you chose to run, your heart would pump faster to get more oxygen around the body and to distribute oxygen to the muscles.

The brain is also involved in the sympathetic nervous system because it decides whether to fight or run.

The Parasympathetic Nervous System

On the opposite side of the spectrum, opposite your sympathetic nervous system, is your parasympathetic nervous system. Now, whether you choose to fight or run, there are parts of your body that are least needed – like for digesting or producing urine. Therefore, the parasympathetic nervous system is your rest and digest system.

What are the parts of the body involved in the parasympathetic nervous system?

  • GI tract
  • Kidneys

You can remember this by imagining that you’re chilling out underneath a cabana. While resting, your heart doesn’t need to race, and your lungs do not require increased amounts of oxygen. If you’re just relaxing, there is no need for the brain, heart, and lungs to speed up and work hard. Therefore, when you’re resting and digesting, other organs that sustain life are activated.

For instance, the GI system can actively create feces or poop which would prompt you that your parasympathetic nervous system is doing its job.

The parasympathetic nervous system does all other activities that aren’t necessary when you’re fighting or running – digesting, creating urine and feces, even distribution of blood to the extremities. 

What to look forward to

In the next video, we will be discussing the different kinds of drugs that influence the sympathetic and parasympathetic nervous systems. We will also be tackling drugs such as:

  • Sympathomimetics and Parasympathomimetics
  • Adrenergic and antagonist
  • Anti-adrenergic receptor

We urge you to watch that video as a continuation of this lecture to gain more insight on the different drugs that affect the nervous system.