Final answer:
The parasympathetic nervous system during its phase reduces heart rate, air passage diameter, and blood flow to muscles, while stimulating digestion, returning the body to a restful state following a fight-or-flight response.
Step-by-step explanation:
During the parasympathetic phase of the fight-or-flight response, the parasympathetic nervous system is responsible for returning the body to a state of rest after a perceived danger has passed. Key processes include reducing the heart rate, narrowing the air passages in the lungs, decreasing blood flow to the skeletal muscles, and stimulating the digestive system to resume its normal functions. This is often termed the 'rest and digest' phase, as opposed to the 'fight or flight' response triggered by the sympathetic nervous system.
The parasympathetic nervous system uses acetylcholine as a neurotransmitter to activate these restorative processes, which are essential for maintaining homeostasis. A good way to remember the role of the parasympathetic nervous system is to associate it with peaceful situations, as both 'parasympathetic' and 'picnic' start with 'p' and convey the notion of relaxation and restoration.
These restorative processes help the body to conserve energy and prepare for future challenges, balancing the body's internal environment following an adrenaline rush associated with the fight-or-flight response.