Which two systems make up the autonomic nervous system?

The autonomic nervous system is predominantly composed of two main divisions: the sympathetic and parasympathetic nervous systems. The sympathetic system is responsible for initiating the body's "fight or flight" response, preparing the body to respond to perceived threats and stressful situations by increasing heart rate, blood flow to muscles, and other physiological changes. In contrast, the parasympathetic system supports the "rest and digest" state, promoting conservation of energy, facilitating digestion, and maintaining homeostasis when the body is relaxed.

This dualistic structure allows the autonomic nervous system to regulate involuntary functions effectively, often working in opposition to maintain balance within the body. For instance, when one system is activated, the other is usually suppressed, which plays a crucial role in body regulation.

The other options refer to various components of the nervous system but do not accurately describe the structure of the autonomic nervous system. Thus, focusing on the sympathetic and parasympathetic divisions is essential for understanding how the autonomic nervous system functions.