Final answer:
The acronym for the parasympathetic nervous system is 'PSNS', which is responsible for the body's 'rest and digest' functions, slowing heart rate, stimulating digestion, and helping to maintain internal homeostasis.
Step-by-step explanation:
The acronym commonly associated with the parasympathetic nervous system is 'PSNS'. The PSNS is a division of the autonomic nervous system responsible for the "rest and digest" set of functions that lead to restful actions and digestion. After the body experiences the fight-or-flight response triggered by the sympathetic nervous system, the PSNS works to return the body to normal. This includes slowing down the heart rate, narrowing air passages in the lungs, and stimulating digestion by reducing blood flow to the skeletal muscles.
The PSNS helps maintain internal homeostasis of the body at times other than after a fight-or-flight response as well. Its activities are often considered to have opposing effects to those of the sympathetic nervous system (SNS). For instance, where the SNS speeds up the heart rate, the PSNS slows it down; where the SNS inhibits digestion, the PSNS stimulates it. These functions contribute to the body's ability to recover and conserve energy after stress.