Final answer:
The parasympathetic nervous system counteracts the sympathetic nervous system's effects by promoting a 'rest and digest' state, which includes lowering heart rate, blood pressure, and enhancing digestion to maintain homeostasis.
Step-by-step explanation:
While the sympathetic nervous system is activated by stressful situations to prepare for a "fight or flight" response, the parasympathetic nervous system is responsible for resetting the organ function following such reactions, thus allowing the body to "rest and digest." The parasympathetic nervous system effectively counterbalances the sympathetic system's effects, reducing heart rate, lowering blood pressure, and stimulating digestion. These functions are vital for maintaining the body's homeostasis, where internal conditions are kept stable despite external changes. The parasympathetic system's activity is usually most prominent during peaceful conditions such as relaxing or after eating a satisfying meal, epitomized by the memory aid of associating 'picnic' with 'parasympathetic' since both start with 'p'.
The parasympathetic nervous system allows animals to "rest and digest" while the sympathetic nervous system is activated in stressful situations. During restful periods, the parasympathetic nervous system is in control, ensuring routine functions are carried out. Preganglionic neurons in the brainstem and sacral spinal cord release acetylcholine onto postganglionic neurons near the target organs. Target organs are influenced by the parasympathetic nervous system, resulting in effects such as lowered heart rate, blood pressure, and stimulation of digestion.