Difference Between Sympathetic and Parasympathetic Nervous System

Main Difference – Sympathetic vs Parasympathetic Nervous System

Sympathetic and parasympathetic sympathetic nervous systems belong to the autonomic nervous system (ANS) in animals. The ANS controls involuntary or reflex functions in the body, including the regulation of the functions of internal organs such as the heart, stomach, and intestine. The sympathetic nervous system originates from the cranial, thoracic and lumbar regions of the spinal cord. The parasympathetic nervous system originates from the cranial and sacral regions of the spinal cord. The main difference between sympathetic and parasympathetic nervous system is that sympathetic nervous system prepares the body for an intense physical activity whereas parasympathetic nervous system relaxes the body by inhibiting high energy functions.        

Key Areas Covered

1. What is Sympathetic Nervous System
      – Definition, Features, Functions
2. What is Parasympathetic Nervous System
      – Definition, Features, Functions
3. What are the Similarities Between Sympathetic and Parasympathetic Nervous System
      – Outline of common features
4. What is the Difference Between Sympathetic and Parasympathetic Nervous System
      – Comparison of Key Differences

Key Terms: Autonomic Nervous System, Central Nervous System, Fight-or-Flight Response, Parasympathetic Nervous System, Spinal Cord, Sympathetic Nervous System

What is Sympathetic Nervous System

The sympathetic nervous system (SNS) is a part of ANS, which prepares the body to respond to stressful situations and is constantly active at the basal level to maintain homeostasis. It extends from the thoracic to lumbar regions of the spinal cord. The SNS mediates the neuronal and hormonal response to stress, which is known as fight-or-flight response or sympathoadrenal response. As a response to pre-ganglionic sympathetic nerve fibers ending at the adrenal medulla, acetylcholine is secreted activating adrenaline and noradrenaline. Adrenaline facilitates the immediate physical actions to prepare the body for violent muscular actions. The sympathetic nerve fibers innervate almost all the organs in the body. The efferent neuronal messages decrease the motility of the digestive tract and urinary output and increase the rate of the heart, metabolic rate, and glycogen breakdown. They also widen the bronchial passages, constrict blood vessels, and dilate the pupil of the eye. The afferent neurons are also involved in carrying sensations like heat, pressure, and pain. The innervation of the SNS is shown in figure 1. 

Figure 1: Sympathetic Innervation 

What is Parasympathetic Nervous System

The parasympathetic nervous system (PSNS) is a part of the ANS, which slows the heart and relaxes muscles. The nerves of the PSNS originates at the middle of the spinal cord. The PSNS functions, in opposition to the sympathetic nervous system and its action, are slower when compared to the sympathetic nervous system. The PSNS stimulates the salivation, digestion, urination, lacrimation, and defecation. Acetylcholine is the neurotransmitter involving in the actions of the PSNS. The stimulation of pre-ganglionic nerve fibers release acetylcholine, and this acetylcholine acts on nicotinic receptors of the post-ganglionic neurons. The stimulation of post-ganglionic receptors release acetylcholine again, and this acetylcholine acts on the muscarinic receptors of the target organ. The innervation of the PSNS is shown in figure 2.

Figure 2: Parasympathetic Innervation

Similarities  Between Sympathetic and Parasympathetic Nervous System

• Sympathetic and parasympathetic nervous systems belong to the autonomic nervous system.
• Both nervous systems originate from the spinal cord.
• Both nervous systems control physiological processes of the body (ex: respiration, digestion, circulation, urination, and reproduction).
• They are involved in maintaining homeostasis of the body.
• They are composed of pre-ganglionic and post-ganglionic neurons.

Difference Between Sympathetic and Parasympathetic Nervous System

Definition

Sympathetic Nervous System: Sympathetic nervous system is a part of the autonomic nervous system that serves to accelerate the heart rate, constrict blood vessels, and raise blood pressure.

Parasympathetic Nervous System: Parasympathetic nervous system is another part of the autonomic nervous system that serves to slow the heart rate, increase intestinal and glandular activity, and relax the sphincter muscles.

Origin

Sympathetic Nervous System: Sympathetic nervous system originates from cranial, thoracic, and lumbar regions of the central nervous system.

Parasympathetic Nervous System: Parasympathetic nervous system originates from cranial and sacral regions of the central nervous system.

Function

Sympathetic Nervous System: Sympathetic nervous system prepares the body for an intense physiological activity.

Parasympathetic Nervous System: Parasympathetic nervous system relaxes the body by inhibiting high energy functions.

Response

Sympathetic Nervous System: The action of the sympathetic nervous system is a quick response.

Parasympathetic Nervous System: The action of the parasympathetic nervous system is a slow response.

Position of the Ganglion

Sympathetic Nervous System: Ganglions of the sympathetic nervous system are found close to the central nervous system.

Parasympathetic Nervous System: Ganglions of the parasympathetic nervous system are found away from the central nervous system but close to the effector.

Pre-ganglionic Fibers

Sympathetic Nervous System: The pre-ganglionic fibers are short in the sympathetic nervous system.

Parasympathetic Nervous System: The pre-ganglionic fibers are long in the parasympathetic nervous system.

Post-ganglionic Fibers

Sympathetic Nervous System: The size of the post-ganglionic fibers is long in the sympathetic nervous system.

Parasympathetic Nervous System: The size of the post-ganglionic fibers is short in the parasympathetic nervous system.

Number of Post-ganglionic Fibers

Sympathetic Nervous System: A large number of post-ganglionic fibers are found in the sympathetic nervous system.

Parasympathetic Nervous System: A small number of post-ganglionic fibers are found in the parasympathetic nervous system

Effective Area

Sympathetic Nervous System: Sympathetic nervous system covers a large area in the body.

Parasympathetic Nervous System: Parasympathetic nervous system covers a small area in the body.

Mode of the Effect

Sympathetic Nervous System: Sympathetic nervous system generates a diffused effect at its target area.

Parasympathetic Nervous System: Parasympathetic nervous system generates a localized effect at its target area.

Releasing Neurotransmitter

Sympathetic Nervous System: Noradrenaline is released at the effector by the sympathetic nervous system.

Parasympathetic Nervous System: Acetylcholine is released at the effector by the parasympathetic nervous system.

Homeostatic Effect

Sympathetic Nervous System: Sympathetic nervous system generates an excitatory homeostatic effect.

Parasympathetic Nervous System: Parasympathetic nervous system generates an inhibitory homeostatic effect.

Effect on Heart Beat, Blood level, and Metabolic Rate

Sympathetic Nervous System: Sympathetic nervous system increases heart beat, blood level, and metabolic rate.

Parasympathetic Nervous System: Parasympathetic nervous system decreases heart beat, blood level, and metabolic rate.

Effect on Sensory Awareness

Sympathetic Nervous System: Sympathetic nervous system raises the sensory awareness.

Parasympathetic Nervous System: Parasympathetic nervous system restores the sensory awareness to the normal level.

Effect on the Pupil of the Eye

Sympathetic Nervous System: Sympathetic nervous system dilates the pupil of the eye.

Parasympathetic Nervous System: Parasympathetic nervous system stimulates the pupil of the eye.

Effect on the Secretion of Saliva

Sympathetic Nervous System: Sympathetic nervous system inhibits the saliva secretion.

Parasympathetic Nervous System: Parasympathetic nervous system stimulate the secretion of saliva.

Effect on the Pulmonary System

Sympathetic Nervous System: Sympathetic nervous system dilates the bronchial tubules.

Parasympathetic Nervous System: Parasympathetic nervous system constricts the bronchial tubules.

Adrenaline Release

Sympathetic Nervous System: Sympathetic nervous system releases adrenaline from adrenaline glands.

Parasympathetic Nervous System: Parasympathetic nervous system have no action on the adrenaline gland.

Effect on Digestive System

Sympathetic Nervous System: Sympathetic nervous system increases the activity of the digestive system.

Parasympathetic Nervous System: Parasympathetic nervous system decreases the activity of the digestive system.

Effect on the Breakdown of Glycogen

Sympathetic Nervous System: Sympathetic nervous system increases the rate of glycogen breakdown.

Parasympathetic Nervous System: Parasympathetic nervous system has no effect on the glycogen breakdown.

Effect on Urinary Output and Rectum

Sympathetic Nervous System: Sympathetic nervous system decreases the urinary output and contracts the rectum.

Parasympathetic Nervous System: Parasympathetic nervous system increases the urinary output and relaxes the rectum.

Conclusion

Sympathetic and parasympathetic nervous systems are two components of the autonomic nervous system of the body in animals. The SNS originates from the thoracic and lumbar regions of the spinal cord and the PSNS originates from the middle of the spinal cord. The SNS prepares the body for stressful situations known as the fight-or-flight response. In contrast, the PSNS relaxes the body and regulates its normal processes. Thus, the main difference between sympathetic and parasympathetic nervous system is their influence on the normal body function.

Reference:

1.”Sympathetic Responses.” Boundless. N.p., 23 Oct. 2016. Web. Available here. 01 July 2017. 
2.”Parasympathetic Nervous System.” GoodTherapy.org Therapy Blog. N.p., 17 Aug. 2015. Web. Available here. 01 July 2017. 

Image Courtesy:

1. “Blausen 0838 Sympathetic Innervation” Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia
2. “Blausen 0703 Parasympathetic Innervation” Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia