How Does the Nervous System Work? And What is the Difference Between the PNS vs. SNS?

Most people do not understand how the human anatomy functions, and the important role that the nervous system plays in our wellbeing. 

According to the NCBI, "The nervous system is made up of all the nerve cells in your body. It is through the nervous system that we communicate with the outside world and, at the same time, many mechanisms inside our body are controlled. The nervous system takes in information through our senses, processes the information and triggers reactions, such as making your muscles move or causing you to feel pain. For example, if you touch a hot plate, you reflexively pull back your hand and your nerves simultaneously send pain signals to your brain. Metabolic processes are also controlled by the nervous system."

The nervous system contains nerve cells that are called neurons, and fire to do a certain task when a "message" is communicated through the nervous system. 

In exercise science, we learned that "neurons that fire together, wire together," and that healthy and unhealthy habits are learned, but also retrainable through retraining the neurons. 

There are two parts of the nervous system, which includes the central nervous system (brain and spinal cord) and the Peripheral nervous system (that connects the CNS to all other areas in the body). 

Under the division of the PNS is the autonomic nervous system (ANS) and the somatic nervous system.

​What we will discuss today are the parts of the nervous system that is under the ANS, which include the parasympathetic nervous system, PNS, (rest and digest phase) and the sympathetic nervous system, SNS (fight or flight). 

The ANS is responsible for involuntary body functions such as blood flow, heart beat, digestion and breathing. Thus, it controls parts of the body that are not under voluntary control. 

The PNS & the SNS are opposites and perform two different functions. One gets you ready for rest and digestion where the other stimulates the body to respond to stress. 

Parasympathetic Nervous System 

This part of the nervous system aides the body in normal functions and conserve physical resources. When activated, most of the blood flow goes to the visceral organs and allows the body to function at normal levels or homeostasis. 

When we sleep, meditate or do yoga, we are activating the PNS. 

Sympathetic Nervous System 

The SNS is opposite where it activates the body to expend energy and respond to external threats and fears. Approximately 85% of the blood flow moves away from the visceral organs to the working muscles of the body and the limbs. When triggered, heart rate and breathing increases, sweat secretion activates and the pupils dilate.  

In reality, we need both parts of the nervous system to function properly. The SNS can save your life if responding to an immediate dangerous situation. And we need the PNS to keep us rested and restored so that you can function in daily life. Both areas of the nervous system encounter biochemical reactions that release certain types of hormones depending on the (lack of) stress or demand on the body. 

However, there are ramifications of being in "fight of flight" for long periods of time. 

​And Why is This Knowledge Important?

It is important to note that the body and the brain receives a biological signal and trigger from physical, emotional, mental or psychological stress. What is important is that the body and brain receives a signal, but cannot tell or discern if that threat is physical or emotional. It is just a biological response, so the brain has no clue the trigger, it just knows its response. 

The brain sends warning signals through the central nervous system. The adrenal glands begin producing hormones (adrenalin and noradrenalin) which are recreated into the body. This causes the heart to beat faster and breathing to become more rapid. Muscles tense and pupils dilate.

So whether you're watching a scary movie, or escaping danger, it is important to know that today, we are under chronic stress response. 

​If you think about society right now, look at all the stress we respond to in our daily life. Traffic, fighting opinions on social media, horror or action-packed movies, news and media reactions, political disagreements, we are constantly triggered by emotional chaos, fear and stress. On top, things like exercise, which is healthy for the body, is also stress and demand on the body.

​WE NEED TO SLOW DOWN! 

​What are the Consequences of Chronic SNS Activation?

Physiologically, this is what people need to understand about the consequences of too much stress on the body. YOU BASICALLY "BURN" OUT OR SECRETE NUTRIENTS THROUGH YOUR URINE. 

When under chronic stress, the nutrient calcium doesn't go to it's function, but rather gets secreted through the urine. When cortisone releases, it leads to a dip in calcium absorption and spikes excretion. 

​Long term nutrient release leads to additional health issues. And when this happens things go south mentally, physically and emotionally. When stressed long term with certain hormones constantly secreting, we crave more comfort food to emotionally fulfill our mental and emotional state. Most of this food lacks nutrients so its a vicious cycle that never ends. The two main hormones released when in the SNS is cortisol and adrenalin (epinephrine). 

According to the Stress and Eating Behavior research study posted it states, "Uncontrollable stress changes eating patterns and the salience and consumption of hyperpalatable foods; over time, this could lead to changes in allostatic load and trigger neurobiological adaptations that promote increasingly compulsively behavior. This association may be mediated by alterations in the hypothalamic-pituitary-adrenal (HPA) axis, glucose metabolism, insulin sensitivity, and other appetite-related hormones and hypothalamic neuropeptides. At a neurocircuitry level, chronic stress may affect the mesolimbic dopaminergic system and other brain regions involved in stress/motivation circuits. Together, these may synergistically potentiate reward sensitivity, food preference, and the wanting and seeking of hyperpalatable foods, as well as induce metabolic changes that promote weight and body fat mass. Individual differences in susceptibility to obesity and types of stressors may further moderate this process."

Chronic SNS activation will eventually put wear and tear on the body. This can lead to injuries, disease, malnutrition, lack of sleep and impaired judgment. Stress is the main reason for SNS and in today's society, we are bombarded with too much stress, especially now emotional chaos. 

We don't feel good about ourselves when under chronic stress. We feel good about ourselves when in homeostasis and living in harmony with the body and mind. 

​Do you have thoughts to share on the PNS & SNS? If so, please share them in the comments below!

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