Final answer:
The sympathetic nervous system prepares the body for 'fight or flight' responses in stress, whereas the parasympathetic nervous system allows for 'rest and digest' during calm periods, maintaining body homeostasis.
Step-by-step explanation:
The sympathetic and parasympathetic nervous systems are two divisions of the autonomic nervous system, which provides unconscious control over visceral functions. The sympathetic nervous system is known for the 'fight or flight' response, activated during stressful situations to prepare the body for action. It increases heart rate, redirects blood to muscles, and releases stored energy. Conversely, the parasympathetic nervous system is active during restful periods, often referred to as 'rest and digest,' and it conserves energy as it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract.