Autonomic Nervous System

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Introduction[edit | edit source]

Autonomic and Somatic Nervous System

The autonomic nervous system is a component of the peripheral nervous system that regulates involuntary physiologic processes. It functions without conscious control throughout the lifespan of an organism to control cardiac muscle, smooth muscle, and exocrine and endocrine glands, which in turn regulate blood pressure, urination, bowel movements, and thermoregulation.. The ANS does this by using many diverse chemicals and signals to maintain homeostasis.

It contains three anatomically distinct divisions: sympathetic, parasympathetic, and enteric.[1][2]See links

Overview[edit | edit source]

The autonomic nervous system operates by receiving information from the environment and from other parts of the body. The sympathetic system is viewed as a quickly responding system that mobilizes the body for action where the parasympathetic system is believed to act much more slowly to dampen responses[3].

  • Sympathetic fibres, located in spinal nerves are responsible for the "fight or flight" response, which is an acute response that takes place in case of an imminent harmful event or intense mental distress. To activate this response, the sympathetic fibres use the neurotransmitter noradrenaline to activate the blood flow in skeletal muscles and lungs, dilating lungs and blood vessels and raise the heart rate.
  • On the contrary, parasympathetic fibres regulate resting responses such as heart rate, salivation, lacrimation (secreting tears), digestion, with the only exception being sexual arousal. Parasympathetic motor fibres are found in four of the 12 pairs of cranial nerves. Synapses established by the parasympathetic fibres are typically inhibitory, with acetylcholine as main neurotransmitter.

Although most of the autonomic nervous system responses are involuntary, they can integrate with the somatic nervous system, which is responsible for the voluntary movements. eg in the case of defecation, there is an interplay between voluntary and involuntary movements[4].

  • The enteric nervous system is confined to the gastrointestinal tract.

Dysautonomia[edit | edit source]

Hand of a person with POTS and dysautonomia exhibiting blood pooling

When the parasympathetic and sympathetic components of the autonomic nervous systems become out of sync, people can experience an autonomic disorder, also called dysautonomia.[3] Dysautonomia is an umbrella term used to describe several different medical conditions that cause a malfunction of the Autonomic Nervous System. The Autonomic Nervous System controls functions of the body that we do not consciously think about. People living with various forms of dysautonomia have trouble regulating these systems, which can result in lightheadedness, fainting, unstable blood pressure, abnormal heart rates, malnutrition, and in severe cases, death. Over 70 million people worldwide live with various forms of dysautonomia. People of any age, gender or race can be impacted. There is no cure for any form of dysautonomia at this time[5]. There are numerous types of autonomic disorders including: Postural Tachycardia Syndrome (POTS); Idiopathic orthostatic hypotension; Multiple system atrophy; Orthostatic hypotension; Postprandial hypotension.[3]

References[edit | edit source]

  1. Waxenbaum JA, Reddy V, Varacallo M. Anatomy, autonomic nervous system.Available: 11.4.2022)
  2. LeBouef T, Yaker Z, Whited L. Physiology, Autonomic Nervous System. InStatPearls [Internet] 2020 Jun 1. StatPearls Publishing. Available; 11.4.2022)
  3. 3.0 3.1 3.2 Very well health What Is the Autonomic Nervous System? Available: (accessed 11.4.2022)
  4. University of Queensland The autonomic nervous system Available: (accessed 11.4.20220
  5. Dysautonomia International What is Dysautonomia )accessed 11.4.2022)