1 THE AUTONOMIC PHYSIOLOGY OF TERROR MANAGEMENT ...

excitatory chronotropic and inotropic influences. However, SNS activity, only when the
PNS is first inactive, can also mildly and temporarily inhibits PNS influence. As a
consequence, only when the PNS is less active does the SNS plays a substantial role in
affecting the heart. When the PNS is more active, it serves to antagonize and greatly limit
the ability for the SNS to affect the heart. Therefore, the PNS effect on the heart may be
viewed as dual. It (1) directly calms the body by slowing the firing of the SA node and
slowing conduction speed at the AV node, and (2) protects the body from fight or flight
related physiological patterns by inhibiting or buffering the excitatory effects of the SNS
on the speed at which the SA node fires, the force of ventricle and atrium contractility,
and the excitability of the ventricles.
Polyvagal Theory
Consistent with the PNS and SNS pattern of interaction put forth above, Porges
(1995) has proposed a Polyvagal Theory that further explicates the function and
components of the PNS and its interaction with the SNS. The Polyvagal Theory proposes
that the PNS consists of two main branches, the smart mammalian vagus and the
vegetative reptilian vagus. In general, the vegetative vagus affects the workings of lower
organs, such as the stomach and intestines, though it also innervates the heart and other
organs, and controls very basic responses and reflexes. Porges posits that this branch
evolved in cold blooded reptiles to help regulate their bodies and responses to the
environment. The reptilian vagal strategy is for vagal tone to be generally or tonically
low, which allows for activity in an animal that does not have an idling sympathetic
nervous system to propel it. However, in reptiles, without the ability to become quickly
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