Autonomic Nervous System | Types & Functions

TAIMOOR AHMED | September 5th, 2023

The autonomic nervous system is that part of your overall nervous system that controls the automatic functions of your body that you need to survive. It is a network of nerves that extend through your head and body and controls unconscious processes without a person’s own effort.

The autonomic nervous system has two main divisions:

  • Sympathetic: This system activates body processes and prepares it for stressful situations, especially in times of emergency, stress or danger. It is responsible for your body’s “fight-or-flight” response. Thus, it increases heart rate and widens (dilates) the airways to make breathing easier. It causes the body to release stored energy. Muscular strength is increased. This division also causes palms to sweat, pupils to dilate, and hair to stand on end. It slows body processes that are less important in emergencies, such as digestion and urination.
  • Parasympathetic: This part of your autonomic nervous system does the opposite of your sympathetic nervous system. This system is responsible for the “rest-and-digest” body processes. It controls body processes during ordinary situations. Generally, it conserves and restores energy. It slows the heart rate and decreases blood pressure. It stimulates the digestive tract to process food and eliminate wastes. Energy from the processed food is used to restore and build tissues.


The autonomic nervous system controls internal body processes such as the following:

  • Blood pressure
  • Heart and breathing rates
  • Body temperature
  • Digestion
  • Metabolism (thus affecting body weight)
  • Immune system
  • The balance of water and electrolytes (such as sodium and calcium)
  • The production of body fluids (saliva, sweat, and tears)
  • Urination
  • Defecation
  • Sexual response

The part of your brain that runs autonomic functions is your hypothalamus. This structure isn’t part of your autonomic nervous system, but is a key part of how it works.

Your autonomic nervous system is a vital part of how you live your life. You don’t even have to think about it most of the time and it will keep doing its job. It is always active, even when you’re asleep, and it’s key to your continued survival.

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