Parasympathetic vs. Sympathetic Nervous System: What's the Difference?

Key Difference

The human nervous system is divided into two portions, one is Central Nervous System (CNS), and other is Peripheral Nervous System (PNS). CNS comprise of the brain and neck whereas PNS covers the whole body below the neck. PNS has further two types, Somatic Nervous system, and Autonomic Nervous system. The somatic Nervous system is responsible for the voluntary actions and functions performed by body muscles. Autonomic Nervous System is responsible for involuntary actions and functions of smooth body muscle and internal organs. Autonomic Nervous System further splits into two types which are Parasympathetic and Sympathetic Nervous system. The sympathetic nervous system activates the psychological response, and parasympathetic system stops it slowly. Both work at the same time against each other. Sympathetic acts and reacts whereas parasympathetic constrain it.

Comparison Chart

  Sympathetic Nervous System Parasympathetic Nervous System
Definition Sympathetic Nervous System is the type of autonomic nervous system which activates due to external effects of stimulus i.e. threat, fear, anger, etc. Parasympathetic Nervous System is the type of autonomic nervous system which controls the body response to the situation, and it works along the sympathetic nervous system.
Function The main function is to control the body in response towards the stimulus. The main function is to control the body response in the state of rest i.e. calmness, etc.
General Body Response  Body tenses up increased muscular activity, body speeds up, more alert and activeness, etc. Works in the opposite direction to sympathetic, cool and calm the body, restore the normal state of the body, slows down the process.
Neuron Fiber Pathways Neurons are very short, and the whole system is quite fast. Long nerve fibers and paths. The system is slower as compare to sympathetic.
Cardiovascular Functioning Increases heart rate. Decreased heart rate.
Muscles Movement Muscles become active and contracts. Muscle moment is slow down, and muscles relax.

 What is Sympathetic Nervous System?

Sympathetic Nervous system is a type of autonomic nervous system which is responsible for activating the body against the stimuli. Whenever a person saw something dangerous in fronts of him like a snake or any other weird thing, his heart rate increases, muscles are contracted, breathing level is increased, eyes are frowning, and other various kinds of feelings of threat and stress are automatically induced in the body. A person could feel all such things because of sympathetic nervous system. It automatically charges up the body and stimulates the internal body organs which react to the situation according to demand. Whenever in any situation of fear, joy, excitement or sudden sadness our sympathetic nervous system initiates the nerve impulses via nerve fibers to the brain resulting in a reaction. This reaction is due to the external or internal stimulus. The reaction that is shown by an individual regarding any of the stimuli is due to the sympathetic nervous system. The responses shown are often referred as ‘fight or flight’ response. It is referred as fight or flight because of the situations in which our body is activated. For example, when our body feels the threat and when we perceive a threat to ourselves, that sympathetic nervous system of our body will work activate all the muscles and organs of the body. In a threat based situation a normal person usually has two choices, and he or she ponder upon those choices either they fight for their survival from the threat or they run or flight away from the threat situation to be safe. It is a very much faster system as compared to the parasympathetic nervous system. The neurons involved in this system are short in size and are linked with nerve fibers within the area of short ends. Whenever the sympathetic nervous system is activated, and it starts its working, the digestion and metabolic process of the person slows down. Additional hormones are released by ductless glands so that the required energy level of the body in that particular state is achieved.


What is Parasympathetic Nervous System?

Parasympathetic Nervous System is the type of autonomic system which is responsible for restoring the body to the normal state after stimulation and ignition done by the sympathetic system. The parasympathetic Nervous system works simultaneously with the sympathetic system. As the sympathetic nervous system in any situation of threat or fear initiates the body activity and enhances the body functioning, this parasympathetic nervous system starts working to cool and calm the body and help the body to get back to its natural position and normal state. It helps in slowing down the muscular activity, decrease the increased heartbeat and another hormone level inside the body. Digestion is slowed down and inhibited by sympathetic system, the parasympathetic system again enhances the process of digestion and increase the metabolic activity. The neurons involved in this process possess longer pathways and larger nerve fibers due to which it is a slow process as compare to sympathetic nervous system.


Parasympathetic vs. Sympathetic Nervous System

  • Sympathetic Nervous System is one of the two types of autonomic nervous system that is responsible for activating the body against the stimulus.
  • Parasympathetic Nervous System is other of the two types of autonomic nervous system that is responsible for restoring the normal state of the body after activation.
  • Both these nervous system works at the same time simultaneously.
  • Sympathetic nervous system is referred as “Fight or Flight” response
  • Parasympathetic nervous system is referred as “Rest or Digest” response.
  • The sympathetic nervous system activates and initiates the body.
  • Parasympathetic nervous system calm and cools down the body.
  • Heartbeat and muscle activity are increased in the Sympathetic
  • Hear beat and muscle activity is decreased in the Parasympathetic
  • The parasympathetic system enhances the digestion process and increases metabolic activity.
  • Sympathetic system decreases the digestion process and slows down metabolic activity.

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