Final answer:
The autonomic nervous system consists of the sympathetic system, which activates the 'fight or flight' response during stress, and the parasympathetic system, which promotes 'rest and digest' activities during relaxation.
Step-by-step explanation:
The autonomic nervous system plays a critical role in regulating involuntary body processes and is divided into two main components: the sympathetic and parasympathetic nervous systems. These two systems often work in opposition to maintain the body's homeostasis, an equilibrium state where biological conditions are optimally sustained.
The sympathetic nervous system activates the body's 'fight or flight' response during perceived threats or emergency situations. It triggers a series of physiological changes like increased heart rate, dilated pupils, and redirected blood flow to muscles, enabling an individual to react promptly to stress.
In contrast, the parasympathetic nervous system supports 'rest and digest' activities when the body is at rest. It conserves energy by slowing down the heart rate, increasing digestive activity, and promoting relaxation of the body. In summary, while the sympathetic nervous system prepares the body for acute stress and heightened alertness, the parasympathetic nervous system calms the body to conserve energy and maintain functions at a basal level necessary for long-term survival.