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Letters to the Editor  |   December 2017
Landmark Article Transforms Traditional View of the Autonomic Nervous System
Author Notes
  • New York Institute of Technology College of Osteopathic Medicine, Old Westbury 
Article Information
Neuromusculoskeletal Disorders
Letters to the Editor   |   December 2017
Landmark Article Transforms Traditional View of the Autonomic Nervous System
The Journal of the American Osteopathic Association, December 2017, Vol. 117, 735. doi:10.7556/jaoa.2017.143
The Journal of the American Osteopathic Association, December 2017, Vol. 117, 735. doi:10.7556/jaoa.2017.143
To the Editor: 
In the February 2017 issue of The Journal of the American Osteopathic Association, Hoehmann and Cuoco1 highlighted the 2017 Science article by Espinosa-Medina et al2 describing the sacral autonomic outflow as sympathetic, not parasympathetic. Researchers used ontogenetic markers and transcription factors to molecularly fingerprint the cells of cranial, thoracolumbar, and sacral autonomic nervous systems. Thoracolumbar and sacral embryologic markers were found to be indistinguishable and distinct from the cranial autonomic system.1 While these findings redefine our understanding of the embryologic development of the sacral autonomics, these data do not address 2 fundamental principles of autonomic nomenclature: structure and function. 
Basic neurophysiology describes preganglionic efferents using acetylcholine as their main neurotransmitter in both sympathetic and parasympathetic models. Postganglionic terminals of the pelvic splanchnic nerves use cholinergic receptors similarly to the cranial efferents of the parasympathetic divisions. This pathway is in contrast to the thoracolumbar sympathetic outflows, which use postganglionic noradrenergic receptors. Additionally, preganglionic thoracolumbar neurons are shorter than their postganglionic counterparts because ganglia are close to the spinal cord. This model is in contrast to the cranial and sacral pre- and postganglionic neurons, which have longer preganglionic neurons with ganglia near the effected organs. These physiologic differences between cranial, thoracolumbar, and sacral systems impart functional distinctions in their effects on different tissues of the body. 
These data encourage a more integrated understanding of traditional “sympathetic-parasympathetic autonomics,” which may be more accurately termed craniospinal autonomics. Craniosacral outflow, therefore, may not be an accurate term for the parasympathetic division. Cranial cholinergic autonomics develop distinctly from spinal autonomics, and spinal autonomics then branch into 2 distinct pathways—thoracolumbar noradrenergic autonomics with sympathetic activity and sacral cholinergic autonomics with parasympathetic activity. So, whereas embryology and neural crest cell migration more accurately define autonomics as cranial vs spinal, anatomic and neurochemical analyses argue a sympathetic vs parasympathetic distinction.3 No evidence exists that the sacral autonomics are not parasympathetic in their effects; therefore, whereas sacral autonomics may be spinal in origin, they are in no functional way “sympathetic.” Although these findings change our understanding of the craniosacral model, they do not affect traditional osteopathic sacral treatments, which are aimed at addressing the parasympathetic nervous system. 
References
Hoehmann CL, Cuoco JA. Landmark article transforms traditional view of the autonomic nervous system [letter]. J Am Osteopath Assoc. . 2017;117(2):72. doi: 10.7556/jaoa.2017.016 [CrossRef] [PubMed]
Espinosa-Medina I, Saha O, Boismoreau F, et al The sacral autonomic outflow is sympathetic. Science. 2016;354(6314):893-898. doi: 10.1126/science.aah5454 [CrossRef] [PubMed]
Neuhuber W, Mclachlan E, Jänig W. The sacral autonomic outflow is spinal, but not “sympathetic.” Anat Rec (Hoboken). 2017;300(8):1369-1370. doi: 10.1002/ar.23600 [CrossRef] [PubMed]