Timothy C. Hain, MD • Page last modified: March 7, 2021
|By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 839, Public Domain, https://commons.wikimedia.org/w/index.php?curid=792179|
The autonomic nervous system controls bodily functions that are run without (much) conscious control. It keeps you alive by regulating your blood pressure, body temperature, breathing, secretions of glands (such as saliva), it allows you to have sex, it keeps the "motor running".
Dysautonomia then is just saying that there is something wrong with this extensive system of wiring. It doesn't mean much because it covers such a large territory. The autonomic nervous system controls sexual activity, and thus persons with erectile dysfunction often have a "dysautonomia".A similarly nearly meaningless statement might be to say someone has a "traumatic brain injury" -- that covers too much territory as well. It is just vague. Dysautonomia covers a huge amount of ground.
Much of the autonomic systems work is carried out by sending messages through nerves to particular glands that secrete neurotransmitters. These have unfortunate and misleading names.
The "sympathetic" nervous system (which has little to do with emotions), carries out its functions by releasing hormones related to adrenalin -- epinephrine, norepinephrine primarily. Examples of sympathetic nervous system actions are dilation of the pupil, increasing heart output, dilating the airway, causing sweat, and facilitating an erection. Thus most of the sympathetic nervous systems action has to do with increasing output of something. The sympathetic system largely sends output first to a set of ganglia in a "chain" running from just below the brainstem to the sacrum, located just outside of the spinal cord. (see red lines on figure on right) From these ganglia post-ganglionic nerves run to the target organ (such as the heart), and release an adrenalin related substance.
The "parasympathetic" nervous system, evidently named just to be different from the sympathetic nervous system, carries out function by releasing acetylcholine. This is a smaller molecule, not considered to be a hormone. Examples of parasympathetic actions are constriction of the pupil, increasing saliva, increasing gut contraction and controlling elimination, and also facilitating secretory aspects of sexual function. There is no "chain" running near the spinal cord as is the case for the sympathetic nervous system, but instead nerves run directly to the target organs (see blue lines on figure above). The vagus nerve in particular carries a large amount of the bodily parasympathetic traffic to target organs, where it synapses there with another cell body, that releases acetylcholine. There are also parasympathetic components to other cranial nerves (such as the oculomotor nerve -- called the "ciliary", going to the pupil), and to sacral nerves (involved with sexual function among other things). Often the outflow portions of the parasympathetic system are named after their ganglions that are close to the target organs.
There are of course myriads of other chemicals released through the nervous system, that fall outside of this general scheme. A newly described chemical subsystem uses nitrogen oxide (NO) as a neurotransmitter, and also seems to be involved with autonomic function. It seems likely that "splitters" will describe other systems.
As the autonomic nervous system goes "everywhere", practically speaking, nearly any disorder of any body part could be potentially blamed on a disorder of the autonomic nervous system. This makes "dysautonomia" a convenient catch-all for situations where people have mysterious disorders that defy simple analysis. There are many articles concerning association of dysautonomia with other vaguely defined conditions.
On this site, we concentrate on dysautonomias related to dizziness and imbalance. It is implausible that the disturbances of the autonomic system cause the inner ear to malfunction, as suggested by Takeda (2006).
On the other hand, disturbances of blood pressure heart rate could reasonably cause a faint feeling, and designated as "dizziness".
Disorders where blood pressure goes too low or pulse too high are commonly attributed to dysautonomia, and discussions of syncope, orthostatic hypotension, and POTs are found on separate pages on this site. These symptom complexes are very common.
There are also disease oriented discussions including Multiple Systems Atrophy, and autoimmune autonomic neuropathy. These disorders are rare. Thus there appear to be a lot more collections of symptoms than there are specific diseases to account for them.
Diabetes is a very large source of dysautonomia as diabetes often damages small nerves which are used to transmit output from the autonomic nervous system to the target organs. (Lakhotia et al, 1997)
There is also a substantial literature about an extremely rare condition -- familial dysautonomia (e.g. Dieterich et al, 2016; Gutierrez et al, 2016). If blood pressure control problems run in your family, you may want to look into this.