A discussion about the Properties of the Autonomic Nervous Sytem sub systems

Please do not refer it to other people (yet)

Purpose of this webpage

The purpose of this web page is to define and discuss the properties of the Autonomic Nervous System (ANS) of human beings and to provide support for these properties by by citing supportive material in the scientific literature. I am writing this page becuase I have been found myself inventing properties of the ANS which may or may not be politically correct, (i.e. currently approved by leaders in the field) .

Overview of Autonomic Nervous System (ANS)

The ANS can easily be described as consisting of three subsystems.

NameMain Function Comment
Sympathetic Nervous Systemfight or flight )
 “quick response mobilizing system” (maybe freeze too?)
Activated to defend against perceived threats
Parasympathetic Nervous System“Rest and digest” or “feed and breed” Activated to heal and restore body functions after SNS activation
Enteric Nervous System intrinsic nervous system of the gastrointestinal system.Will not be discussed further.
Table 1: Three subdivisions of Autonomic System

Next we will consider the respective properties of the two major divisions of the Autonomic Nervous System.,

Sub SystemSNS ActivePSNS ActiveComment
FearSense of impeding threat to life, limb, and ego. Amygdala triggers and a bunch of body systems get ready to protect and defendAcceptance of whatever is happening in the here and now. Emotions are calm peaceful, connecting etc.May be the underlying cause of all the other subsystems
ActivityFlight/Flee/FreezeMoving Peacefully
Future FearConfidence/hope
Heart Rate VariabilityHF/HRV high, Respiratory Sinus Arrythmia high
VagusVagal tone high
Table 2, Suggested opposite emotional states/actions for active SNS versus active PSNS

Sub System discussions

Activity Subsystem

Fear Subsystem


Feeling Subsystem

Future Subsystem

Interconnectedness Subsystem

Heart Rate Variability Subsystem

We can observe the activity levels of the SNS and PSNS by doing a spectral analysis of HRV.
Shaffer and Ginsberg (2017) give an overview of Heart Rate Variability (HRV) and state “Two distinct but overlapping processes generate short-term HRV measurements. The first source is a complex and dynamic relationship between the sympathetic and parasympathetic branches. The second source includes the regulatory mechanisms that control HR via respiratory sinus arrhythmia (RSA).”). (p 5 of 36)
The HF or respiratory band is (0.15–0.40 Hz)
“The assumptions underlying the LF/HF ratio is that LF power may be generated by the SNS while HF power is produced by the PNS. In this model, a low LF/HF ratio reflects parasympathetic dominance.” (p 11 of 36)
“This is seen when we conserve energy and engage in tend-and-befriend behaviors.” In contrast, a high LF/HF ratio indicates sympathetic dominance, which occurs when we engage in fight-or-flight behaviors or parasympathetic withdrawal.” {p11/36)

Vagus Nerve Subsystem


Claisse et al ( 2017) Heart rate variability changes and emotion regulation abilities in short- and long-term abstinent alcoholic individuals

Drug and Alcohol Dependence

Volume 175, 1 June 2017, Pages 237-245

Shaffer. F and Ginsberg, J (201 7) An Overview of Heart Rate Variability Metrics and Norms. Public Health, 2017;5.;258. September 28,2017  https://doi.org/10.3389/fpubh.2017.00258

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