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.