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.

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.