“Fight or Flight” or “Rest and Digest”
You have probably heard of this expression at some point and experienced it before, but why does it happen? How does it work?
The Autonomic nervous system is the part of the nervous system that happens automatically without us subconsciously making the process begin. The Autonomic Nervous System affects urination, respiration, digestion, sexual behavior, stress, and the sleep/wake cycle. The main point of the Autonomic system is to keep us alive.
The two main branches of the Autonomic nervous system are the sympathetic nervous system and the parasympathetic nervous system. These systems have an inverse relationship, so they act in opposite ways.
The Sympathetic Nervous System (SNS)
The SNS is your “Fight or Flight” (Some may include “Freeze”). The SNS is the stress response that adrenergic activators activate when you are in a life-or-death situation. When in fight or flight, your body puts digestion, urination, salivation, and defecation on the back burner. Those things do not matter if you are in a perceived life or death moment.
Instead, The body shunts blood to vital organs and your muscles so you can run. Hormones like adrenaline (epinephrine), cortisol, and noradrenaline (norepinephrine) are circulating in your bloodstream, increasing your heart and respiratory rate. These hormones put you in a vigilant state to make quick decisions.
- Adrenaline, also called epinephrine, is a hormone that causes an increase in heart rate and increases respiration efficacy as well as blood glucose to have energy readily available.
- Similarly, Cortisol is a steroid hormone produced by the adrenals and is released to increase glucose levels. Cortisol is involved in the SNS to give you the quick energy you need. We talked about Cortisol in another blog, which is linked here- https://wonderfullymade-kmk.com/how-to-balance-blood-glucose/.
- Noradrenaline, also called norepinephrine, affects blood vessels, inherently affecting blood pressure. Your blood vessels are like a water hose. Did you ever put your thumb over the opening to spray your siblings during the summer or trick them into thinking it was raining? Constricting the flow increases the pressure, causing the water to come out faster.
Similarly, in the body, it increases blood pressure and heart rate. But the pressure decreases once you take your thumb off the water hose opening, and the stream slows. This analogy is the best one I heard from my nursing school professor. Shout out to Mr. Miller.
How the SNS affects our sight
The sympathetic nervous system also vasodilates the pupils (Mydriasis). I remember this because vasodilation D helps you see distance D.
Note: I know what you are thinking. Wait, Kati, I thought that when you go to the eye doctor and get your eyes dilated, they tell you that you may have blurry vision. That is true, but don’t get confused because the blurry vision is from when you are trying to look at things up close when pupils are dilating. Remember, dilation is good for seeing distance, not up close. The pupils dilate to let in more light, which increases the ability to see.
The Parasympathetic Nervous System (PNS)
Cholinergic activators activate the other branch of the Autonomic Nervous System; the Parasympathetic Nervous System (PNS) is your “Rest and Digest”. Interestingly, this nervous system causes your pupils to vasoconstrict (Miosis). Vasoconstricts C so you can see close-up C.
I remember this with the parasympathetic system this way. If I’m sitting, relaxing, and reading a book or scrolling on the phone, my eyes only have to see the page or the screen, so my eyes will be focusing close to me. If it is close to me, it is cholinergic. The cholinergic effects are the opposite of the adrenergic effects.
Therefore, blood goes to the intestines and stomach to help with peristalsis. Salivary glands produce saliva to help with mastication. You will be able to urinate, defecate, and rest. The hormone involved with this system is Acetylcholine, which slows your heart rate. Your respiratory rate will be low and slow as well.
Memory Tricks
Some memory tricks I came up with in nursing school for this content were Parasympathetic “Peace” -> “Calm” Cholinergic. Sympathetic “Stress” -> “AHHHH” Adrenergic. I am a pneumonic visual learner, so if you also learn better when you see it in a diagram or table form, I have a template you can receive by joining the email list. Or you can locate it on my Pinterest account: https://pin.it/6YxWAxu
God, thank you for those who are taking the time to read these posts today. I pray that they can see how our bodies are so complex and there is no way we just appeared from anywhere other than an intentional creator. May you be glorified by every word and every breath. To you the honor, glory, and praise forever. Amen.