The peripheral sympathetic neurons arise from the mesoderm, neural crest.
The ANS in general regulates physiological processes.
The newborn uses primitive brainstem-visceral circuits via ingestive (eating and drinking) behaviors as the primary mechanism to regulate physiological states.
During the first year of life (already starting in the third trimester of the pregnancy), the cortical regulation of the brainstem develops.
2 important sequential phases in the neurophysiological development arise:
• The development of the myelinated vagus system during the last trimester.
• The development of cortical regulation of the brainstem which regulates the vagus nerve functions during the first year postpartum.
At birth, the central ANS is maturing and at that time it is vulnerable to adverse environmental and physiological influences.
Critical connections are formed early in development between the ANS and the limbic system to integrate psychological and body responses.
The unmyelinated, more primitive, vagus nerve is the first autonomic branch to develop in fetal life but does not have significant function prior to birth.
Note: the myelinated branch of the vagus nerve controls facial muscles associated with speaking, swallowing, sucking and, most importantly, breathing. It also regulates ANS pathways to the heart and can rapidly initiate relaxation and calm.
The myelinated vagus fibers send signals to the brain much more quickly than the phylogenically older, unmyelinated fibers. As a result, the myelinated vagus system in mammals can override the signals of the ANS, a phenomenon that is called the vagal brake.
The vagal brake’s essential function is to regulate heart rate through the rapid inhibition and disinhibition of vagal tone to the heart.
When the brake is released, the sympathetic part becomes dominant, and heart rate increases to catalyze the system in response to environmental demands.
When the brake is impaired for any reason, phylogenically older autonomic responses are activated, resulting in a narrowed repertoire of fight or flight behaviors.
In infants and young children, studies show that vagus tone is an important indicator of self-regulation, sustained attention, resiliency and the ability to calm down after experiencing a stressor.
Osteopathy: this is possibly the explanation why gentle high cervical techniques in children (cranial base release, compression 4th ventricle…) stimulate the vagus system whereby the general vagus tone increases. This improves several functions in children such as sleep, calmness, well-feeling, digestion, heart functions, respiration…
Beside the posterior high cervical techniques, osteopaths should not forget to also treat the ventral soft tissues of the upper neck.
More techniques can be found in my book ‘Scientific Osteopathic Approach to Patients with Cervical Complaints and Headache’.