The parasympathetic nervous system (PSNS) is one of the two divisions of the autonomic nervous system (ANS). The PSNS is known as the “rest and digest” system, “feed and breed”, or the “relax, repair & reproduce” system. It is also called the craniosacral division of the autonomic nervous system because it originates at some of the cranial nerves and sacral nerves. This division of the ANS helps the body to conserve energy, and should be dominant when the person is not in a crisis. Relaxing activities such as massage, meditation, a warm bath, and other enjoyable activities can stimulate the parasympathetic nervous system. These are reflexive effects of massage (not mechanical effects).

Physiological effects of stimulating the parasympathetic nervous system:

Decreased heart rate and force of contraction
Decrease in blood pressure
Pupils constrict
Skeletal muscles relax
Bronchial tubes in lungs constrict
Peripheral vasodilation (decreased vascular resistance)
Stimulation of salivary glands
Digestive enzymes are released
Increased intestinal motility
Contraction of the urinary bladder and relaxation of sphincter
Changes in various hormone levels (e.g. decreased stress hormones such as cortisol)

There is another part of the autonomic nervous system that you may see in some sources called the enteric nervous system. It influences a lot of the body’s digestive functions. I doubt you will see any reference to the enteric system on the MBLEx, so just stick with studying the parasympathetic and sympathetic divisions of the ANS.

Sympathetic Nervous System

Chronic stress results in a perpetual state of increased sympathetic nervous system (SNS) activation. The sympathetic nervous system is an important survival system that gets you body ready for “fight or flight” (or “fight, fright or flight”). It is also called the thoracolumbar division of the autonomic nervous system because of where the nerves originate. It prepares the body for a perceived threat. But chronic overactivity of the SNS is detrimental to health.

Here are some of the physiological effects of SNS activation:

Increased heart rate and strength of contraction (increased cardiac output)
Increased blood pressure
Bronchial tubes dilate (to facilitate O2-CO2 exchange)
Digestion slows or stops
Stored glycogen is converted to glucose (usable fuel for muscles)
Muscles tense up
Peripheral vasoconstriction (cold hands & feet)
Changes in various hormone levels

“Rest and digest” or “Feed-and-breed” or “Relax, repair and reproduce”

parasympathetic nervous system

Decreased blood pressure
Decreased muscle tension
Increased peripheral circulation due to vasodilation
Improved digestion

sympathetic nervous system or thoracolumbar nervous system

By causing the body and mind to relax.

Previous Topic

Back to Lesson

Next Topic