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.
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.
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.
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: