Final answer:
The sympathetic nervous system is activated during stressful situations to enable a 'fight or flight' response, with physiological actions that prepare the body to face the threat. After the stress diminishes, the parasympathetic nervous system restores the body to a calm state.
Step-by-step explanation:
During times of heightened stress, the body's sympathetic nervous system is activated. Contrary to the activation of the parasympathetic nervous system during restful states that allows for 'rest and digest' activities, the sympathetic nervous system prepares the body for a 'fight or flight' response. This is an automatic, rapid response where physiological changes occur such as dilation of pupils, increase in heart rate and blood pressure, relaxation of the bladder, and release of glucose from the liver. Once the stress subsides, the parasympathetic nervous system takes over to bring the body back to a state of rest and normal functioning.