Autonomic Nervous System

The autonomic nervous system (ANS) regulates the functions of our internal organs (the viscera) such as the heart, stomach and intestines. The ANS is part of the peripheral nervous system and it also controls some of the muscles within the body. We are often unaware of the ANS because it functions involuntary and reflexively. For example, we do not notice when blood vessels change size or when our heart beats faster.


The ANS is most important in two situations:

  • In emergencies that cause stress and require us to “fight” or take “flight” (run away) 
  • In non-emergencies that allow us to “rest” and “digest.” 
There are two branches of the autonomic nervous system – sympathetic and parasympathetic (vagal) nervous systems that always work as antagonists in their effect on target organs.

Sympathetic nervous system. For most organs including heart the sympathetic nervous system stimulates organ functioning. An increase in sympathetic stimulation causes increase in HR, stroke volume, systemic vasoconstriction, etc. The heart response time to sympathetic stimulation is relatively slow. It takes about 5 seconds to increase HR after actual onset of sympathetic stimulation and almost 30 seconds to reach its peak steady level. 

Parasympathetic nervous system. In contrast, the parasympathetic nervous system inhibits functioning of those organs. An increase in parasympathetic stimulation causes decrease in HR, stroke volume, systemic vasodilatation, etc. The heart response time to parasympathetic stimulation is almost instantaneous. Depending on the actual phase of the heart cycle it takes just 1 or 2 heartbeats before heart slows down to its minimum, proportional to the level of stimulation. 

At rest both sympathetic and parasympathetic systems are active with parasympathetic dominance. The actual balance between them is constantly changing in an attempt to achieve optimum, taking into account all internal and external stimuli.


Autonomic Dysfunction or Dysautonomia - problems with this autonomic nervous system. 

Problems with the ANS can range from mild to life threatening. Sometimes only one part of the nervous system is affected. In other cases, the entire ANS is affected. Some conditions are temporary and can be reversed, while others are chronic and will continue to worsen over time. Diseases such as diabetes or Parkinson’s disease can cause irregularities with the ANS. Problems with ANS regulation often involve organ failure, or the failure of the nerves to transmit a necessary signal. 


Symptoms of Autonomic Dysfunction 

Effects of autonomic dysfunction can include just a small part of the ANS, or the entire ANS. Some symptoms that may indicate the presence of an autonomic nerve disorder include: 

  • Dizziness and fainting upon standing up (orthostatic hypotension) 
  • Inability to alter heart rate with exercise (exercise intolerance) 
  • Sweating abnormalities, which could alternately be too much sweat or insufficient sweat
  • Digestion difficulties due to slow digestion. Resulting symptoms could include loss of appetite, bloating, diarrhoea or constipation and difficulty swallowing. 
  • Urinary problems. These can include difficulty starting urination, incontinence and incomplete emptying of the bladder. 
  • Sexual problems and dysfunction. 
  • Vision problems. This could be blurry vision or the failure of the pupils to react quickly enough to changes in light.


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