Sympathetic vs Parasympathetic

Last Updated: April 28, 2024

Sympathetic vs Parasympathetic

The autonomic nervous system (ANS) is a critical component of the human body that regulates a variety of involuntary physiological processes, including blood circulation, digestion, and breathing. Operating independently from our conscious awareness, the ANS ensures the maintenance of internal stability and balance, known as homeostasis. By controlling essential functions such as heartbeat, breathing rate, body temperature, and more, this system plays a pivotal role in our daily survival.

Within the autonomic nervous system, there are two main subdivisions that work in tandem to maintain bodily functions: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is often characterized as the body’s “fight or flight” response, activating during times of stress to prepare the body for rapid action. In contrast, the parasympathetic nervous system is associated with “rest and digest” activities, promoting relaxation and conservation of energy.

Difference between Sympathetic and Parasympathetic

Sympathetic Autonomic Nervous System: Located along the thoracic and lumbar regions of the spinal cord, the sympathetic nervous system prepares the body for rapid, emergency responses, known as the “fight-or-flight” reaction. It increases heart rate, speeds up respiration, and dilates pupils to enhance survival-critical bodily functions.

Parasympathetic Autonomic Nervous System: In contrast, the parasympathetic nervous system, situated between the brainstem and the sacral spinal cord, manages the “rest and digest” activities that conserve and restore energy. It slows the heart rate, reduces respiration, and stimulates digestive processes, supporting functions that aid in relaxation and recovery.

AspectSympathetic Nervous SystemParasympathetic Nervous System
Primary FunctionPrepares the body for stress or emergency situations (fight-or-flight response).Promotes the maintenance of the body at rest (rest-and-digest response).
Origin of Nerve FibersThoracolumbar region of the spinal cord.Craniosacral region (brainstem and sacral spinal cord).
NeurotransmittersMainly uses norepinephrine (noradrenaline).Primarily uses acetylcholine.
Effects on HeartIncreases heart rate and the force of heart contractions.Decreases heart rate and the force of heart contractions.
Effects on LungsDilates bronchi, which increases air flow to the lungs.Constricts bronchi, which reduces air flow to the lungs.
Effects on EyesDilates pupils to improve vision.Constricts pupils and focuses the lens for near vision.
Effects on DigestionInhibits digestive activity.Stimulates digestive activity.
Effects on Salivary GlandsProduces thick, viscous saliva.Produces watery saliva to aid in digestion.
Effects on BladderRelaxes the bladder.Contracts the bladder to promote urination.
Effect on Blood VesselsGenerally constricts blood vessels in the skin and abdominal organs, but dilates blood vessels in muscles.Generally has little effect on blood vessels, but may cause dilation in the genital areas to enhance function.
Energy MobilizationStimulates the release of glucose from energy stores.Promotes the storage of glucose.
Response TimeRapid response to stress, preparing for quick action.Slower, more sustained response, geared towards conservation and restoration of body resources.

Key Similarities Between Sympathetic and Parasympathetic Nervous Systems

  • Both Systems Belong to the Autonomic Nervous System: Both the sympathetic and parasympathetic nervous systems serve as integral components of the autonomic nervous system, which governs the body’s involuntary functions.
  • They Regulate Vital Functions Automatically: These systems automatically regulate vital functions, ensuring the body appropriately responds to different situations without conscious effort.
  • They Operate Antagonistically to Maintain Homeostasis: Generally, these systems work in opposition to maintain homeostasis. When one system activates, the other typically recedes.
  • Both Use Neurotransmitters for Communication: The sympathetic and parasympathetic nervous systems use neurotransmitters to communicate with the body’s organs and glands.
  • Each System is Critical for Survival: Both systems play critical roles essential for survival, influencing various physiological processes.

Key Differences Between Sympathetic and Parasympathetic Nervous Systems

  • Differing Primary Roles: The sympathetic system prepares the body for energetic, emergency actions, while the parasympathetic system supports routine operations and conserves energy.
  • Effects on the Body Vary: Sympathetic activation typically stimulates organ functions that support rapid physical action, whereas parasympathetic activation supports activities that conserve and restore body resources.
  • Different Trigger Points: Perceived threats or emergencies trigger the sympathetic system, while the parasympathetic system predominates during relaxed states.
  • Impact Varies Across Organ Systems: Depending on which system dominates, different organ systems either activate or suppress, reflecting their roles in survival versus rest.
  • Direction of Activity Differs: Sympathetic actions generally affect many organs simultaneously and are diffuse, whereas parasympathetic effects are more targeted and specific.


What is the Difference Between Sympathetic and Parasympathetic?

The sympathetic nervous system triggers the fight-or-flight response, while the parasympathetic system promotes rest and digestion.

How to Remember the Difference Between Sympathetic and Parasympathetic?

Remember “Sympathetic = Stress” and “Parasympathetic = Peace” to differentiate their primary functions easily.

Is Stress Sympathetic or Parasympathetic?

Stress activates the sympathetic nervous system, preparing the body for quick action and response.

Is Increased Blood Pressure Sympathetic or Parasympathetic?

Increased blood pressure is typically a result of sympathetic nervous system activation, which constricts blood vessels.

How Do You Calm Your Parasympathetic Nervous System?

To calm the parasympathetic nervous system, engage in relaxing activities like deep breathing, meditation, or yoga.

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