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Difference Between Sympathetic and Parasympathetic Nervous System


Before knowing the difference between the sympathetic and parasympathetic nervous systems, we should first understand the autonomic nervous system. It is the primary controlling system of our body that specifically involves the processes of blood circulation, breathing, digestion, and urination, etc. The main reason for naming it is because it functions autonomously, which means working involuntarily.

Homeostasis is considered a fundamental function of the autonomic nervous system apart from all the systems mentioned above. It is the ability to maintain an internal environment despite several changes in the surrounding.

There are two major types of the autonomic nervous system, the Sympathetic Nervous System, and the Parasympathetic Nervous System.

Let’s take a glance at their comparison table below!

 Sympathetic Nervous SystemParasympathetic Nervous System
OriginFrom the thoracic, cranial, and lumbar system of CNSFrom the sacral and cranial system of CNS
Ganglion PositionAway from effector, and close to spinal cordClose to effector, and away from spinal cord
Pre-ganglionic Fiber SizeShortLong
Post-ganglionic Fiber SizeLongShort
Activation of ResponsesFight & flightRest & digest
Neuron PathwaysFast system with very short neuronsSlow system, longer pathways  

Sympathetic Nervous System – Brief Explanation

The primary function of the sympathetic nervous system is to control the “fight and flight” responses in the body. As this system arises from the spinal cord, particularly the lumbar and thoracic regions, it manages to deal with the external danger.

Parasympathetic Nervous System – Brief Explanation

The primary function of the parasympathetic nervous system is to control the “rest and digest” systems in the body. This system originates from the medulla and spinal cord to control homeostasis, internal maintenance of a body.

Know the Similarities Between Sympathetic and Parasympathetic Nervous System

Despite being opposite in managing a body’s internal system, both of them have a few similarities that are discussed below:

Parts of ANS

Either its sympathetic or parasympathetic system, both are the main parts of the autonomic nervous system.


Both the nervous systems commonly originate from the spinal cord.

Effect of Physiological Processes

it doesn’t matter if it is the sympathetic or parasympathetic nervous system both significantly affect the body’s physiological processes, such as reproduction, circulation, respiration, digestion, and urination, etc.


Both systems play a major part in maintaining homeostasis, an internal temperature of a body.


Sympathetic and Parasympathetic nervous systems consist of pre-ganglionic and post-ganglionic neurons.

Check Out the Differences between Sympathetic and Parasympathetic Nervous System

Both of the autonomic nervous systems have a major role in maintaining different situations of a body. While the sympathetic system controls the emergencies, the other functions to balance and restore it. Let us discuss a few more common differences between the two.

How Do These Nervous Systems Respond?


After the activation of this nervous system, a living organism accelerates, tenses up, and gets more careful. Here are the primary responses by a sympathetic nervous system:

  • Increase in heart rate
  • Constriction of the heart
  • Contraction of smooth muscles
  • Contraction of sphincters
  • Dilation of the eye pupils and bronchial tubes in the lungs
  • The decrease in the process of urination
  • Freeing up adrenaline from adrenal glands
  • Shutting down of all the unimportant processes of survival
  • Production of energy for muscles by the conversion of glycogen to glucose
  • Reduction in the production of saliva


While on the other hand, the parasympathetic system works to balance the sympathetic nervous system. It contributes to maintaining the calm state of a body. Below are the primary responses by this system:

  • Reduction in heart rate
  • Relaxation of smooth muscles
  • Relaxation of sphincters
  • Constriction of eye pupils and bronchial tubes in the lungs
  • Increase in the process of urination
  • More saliva production for increased digestion

Working of the Nervous Systems


This system is known as a faster system with movements along the short neurons in the body. The sympathetic system triggers the adrenal medulla to discharge chemical receptors and hormones into the bloodstream. Moreover, the targeted muscles and glands get excited too. Soon after the attacking danger is all gone, the other autonomic nervous system takes over to balance the body’s working.


As discussed above, this system works to counterbalance the sympathetic system. Parasympathetic is a slower mechanism with movements along the higher pathways. This system usually functions by activating the preganglionic fibers from the spinal cord or medulla that works nearby the target unit. They are set to produce a synapse that helps in activating the desired response.


The overall differences between sympathetic and parasympathetic nervous systems make them two distinct types of the autonomic nervous system. Both methods work one after the other. If the former activates the fight and flight situation of the body, the latter counterbalances these activities to the rest and digest condition. Either it’s sympathetic or parasympathetic system, both hold their own significance for the daily working of a body.

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