Final answer:
The sympathetic nervous system activates the fight-or-flight response, increasing metabolism during emergencies, whereas the parasympathetic nervous system promotes rest and digestion, reducing metabolic rates and conserving energy.
Step-by-step explanation:
The autonomic nervous system plays a crucial role in regulating metabolism through its two components: the sympathetic and parasympathetic systems. The sympathetic nervous system is known for its "fight-or-flight" response, which gears the body up for emergency situations. This includes increasing heart rate, dilating air passages in the lungs, elevating blood flow to muscles, and temporarily inhibiting processes such as digestion. Contrarily, the parasympathetic system enacts the "rest and digest" mode, calming the body post-stress by slowing the heart rate, constricting air passages, reducing blood flow to muscles, and reactivating the digestive system. Consequently, metabolism ramps up under sympathetic control when energy is needed rapidly, and it slows down under parasympathetic influence, focusing on conservation and nutrient absorption.