The Sympathetic Nervous System is a division of the autonomic nervous system that prepares the body for stress, danger, or emergencies. It is responsible for the “fight-or-flight” response, which activates a series of physiological changes to enable the body to respond quickly and effectively to perceived threats.


  • Sympathetic Chain Ganglia: Also known as the paravertebral ganglia, these are a chain of interconnected ganglia located bilaterally on either side of the spinal cord.
  • Prevertebral Ganglia: These ganglia are situated anterior to the spinal column and are responsible for innervating the abdominal and pelvic organs.


The sympathetic nervous system plays a crucial role in physiological responses related to stress and survival. Its main functions include:

  1. Increased Heart Rate: The sympathetic system stimulates the heart, leading to an increase in heart rate and cardiac output in order to supply more oxygen and nutrients to the muscles and organs.
  2. Dilation of Pupils: The sympathetic system causes the dilation of pupils, allowing more light to enter the eyes and enhancing visual sensitivity.
  3. Bronchodilation: It facilitates the relaxation of smooth muscles in the bronchi, resulting in the dilation of airways and increased oxygen intake.
  4. Release of Adrenaline: The sympathetic system triggers the adrenal glands to release adrenaline (epinephrine) into the bloodstream, which further enhances the fight-or-flight response.
  5. Inhibition of Digestion: During sympathetic activation, blood flow is diverted away from the digestive organs, resulting in the inhibition of digestive processes.
  6. Elevation of Blood Pressure: Constriction of blood vessels in non-essential areas helps redirect blood flow to vital organs, increasing blood pressure and supplying nutrients where they are needed most.
  7. Mobilization of Energy: The sympathetic system promotes the release of stored glucose (glycogen) in the liver, providing energy for the body to respond effectively to stressors.


The sympathetic nervous system can be activated by various stimuli, including physical threats, emotional stress, exercise, and certain drugs. Activation of this system prepares the body for action and enables it to effectively deal with the challenges at hand.