Which component of the nervous system reacts to stimuli?

The correct answer is the receptor because it is specifically designed to detect and respond to various stimuli from the environment. Receptors can be found throughout the body and are specialized to sense changes such as temperature, light, pressure, and chemicals. When these stimuli are detected, receptors convert the information into electrical signals that can be transmitted to other parts of the nervous system for processing.

In contrast, neurons serve as the specialized cells that transmit these electrical signals, but they do not directly respond to stimuli; they relay the information. Effectors, like muscles or glands, perform the action or response, such as moving a limb or secreting a hormone. Synapses are the junctions between neurons where communication occurs, but they are not involved in detecting stimuli themselves. Therefore, receptors are the initial component in the nervous system that reacts to stimuli by converting them into signals that the nervous system can interpret.