What body system is responsible for detecting changes in the internal and external environments and coordinating responses?

The nervous system is crucial for detecting changes in both internal and external environments and coordinating appropriate responses. It consists of the brain, spinal cord, and a network of nerves that transmit signals throughout the body. When a change occurs—such as touching a hot surface—the nervous system quickly processes the information, sends signals to the muscles to react, and can also trigger various involuntary responses. This ability to receive sensory input, interpret it, and respond effectively is essential for maintaining homeostasis and ensuring the safety and functionality of the organism.

In contrast, the circulatory system primarily focuses on the transportation of blood, nutrients, and waste throughout the body but does not play a direct role in environmental detection and response coordination. The muscular system is responsible for movement and stability but relies on the nervous system to receive commands and stimuli. The respiratory system is mainly concerned with gas exchange and does not coordinate responses to changes in the environment directly. Thus, the nervous system stands out as the primary system for sensing and responding to changes around us.