Responses of Nervous System 

The Nervous system is composed of a complex network of neurons and supporting cells and is essential for regulating bodily functions. It is categorized into two broad categories: central nervous system and peripheral nervous system. These are further divided into autonomic and somatic nervous systems. Autonomic nervous system is a significant component of the nervous system and it plays the most important role in regulating our involuntary physiological responses towards stimuli in the environment. This is further divided into two systems called sympathetic nervous system and parasympathetic nervous system. Each of these branch have different effects on the body and they work together in opposition to maintain a homeostasis within the body. Sympathetic nervous system is responsible for the arousal and bodily changes in response to stimulation from environment while parasympathetic system functions to calm down the body after the stress response. 

Sympathetic Nervous System: Fight vs Flight 

Commonly referred to as the flight/ fight response or acute stress response is a function of the sympathetic nervous system in reaction to a stressful, threatening or emergency situation. On  activation, SNS triggers a number of physiological changes in the body.

Increased Heart Rate

To make sure in an emergency situation muscles have sufficient supply of oxygen and nutrients, blood vessels constrict which increases the blood pressure. Heart rate is also elevated to pump the blood flow towards major muscles in the body.

Dilated Pupils 

In order to improve vision it allows more light to enter the eye by dilating pupils, hence, increasing the probability to detect any danger or threat. 

Dilation in Lungs 

SNS (Sympathetic Nervous System) allows the airways in lungs to expand to provide increased levels of oxygen for breathing and respiration.

Release of Energy 

Glucose is released directly into the bloodstream from the liver to provide instant energy to fight or flee from the threat.

Inhibited Digestion 

Digestive processes are slowed down, blood flow and energy is directed towards other organs to ensure the availability of oxygen and energy for survival.

Arousal 

Adrenal glands are stimulated and release adrenaline also known as epinephrine. It is responsible for arousal and helps in activation of the body to immediately respond to threat, danger or any emergency situation.

Parasympathetic Nervous System: Rest and Digest 

After a stressful or arousing situation is resolved, the parasympathetic system gets activated to relax the body and maintain a neutral optimal state of the biochemicals within it. It is commonly referred to as the rest and digest system as it is activated in the absence of a threatening stimulus, promoting bodily maintenance and energy conservation. 

It is characterized by following changes in the body.

Decreased Heart Rate and Blood Pressure 

In the resting state, blood vessels are expanded and heart rate is reduced. It helps the body relax and remain in a calm state. 

Constricted Pupils 

Pupils are constricted to improve near vision.

Lung Constriction

Now that the emergency situation is over, it is the responsibility of the parasympathetic system to maintain neutral oxygen levels, hence airways towards lungs are constricted as the oxygen demand is decreased due to resting state of body. 

Active Digestion

Digestive system is activated, saliva production is enhanced, enzymes are released to actively break down the food and absorb nutrients. 

Energy Storage 

In the resting state, PNS allows the body to conserve energy for future use by storing sugars and fats.

Homeostasis 

Sympathetic and parasympathetic nervous systems work together to create a balance within the body. Both these systems are crucial to respond appropriately to various situations depending on the requirement such as action or relaxation. SNS maintains arousal when needed and PNS relaxes and brings body to neutral states once the emergency situation is resolved. For example, if a person is flight and encounters turbulence, their SNS will be activated it will  increase their heart rate, blood pressure, energy and their body will be in a state of arousal. After a few minutes when the turbulence has passed and situation is perceived as being safe, PNS will be activated to relax the body, decrease the heart rate and blood pressure and bring back the body into a neutral state.Both these responses are essential for survival.

Dysregulation In these systems can lead to various health complications.Overactive SNS leads to chronic stress, inflammation, low immunity, and increases likelihood of stroke, cardiovascular disorders and hypertension.

A take away message will be that understanding the mechanisms of sympathetic and parasympathetic nervous systems is important to manage stress and relaxation.It provides a better insight into how the body responds and how we can better take care of it.Relaxation techniques,mindfulness, meditation and physical activity help maintain a healthy balance between these two autonomic systems. 

References 

Ludwig, P. E., Reddy, V., & Varacallo, M. (2022, October 10). Neuroanatomy, central nervous system (CNS). StatPearls – NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK442010/