What is an example of an effector in the body?

An effector in the body is a structure that produces an effect or response to a stimulus, and muscle fibers are prime examples of effectors. They contract and cause movement in response to signals from the nervous system. When a nerve impulse reaches a muscle fiber, it triggers the fibers to contract, leading to actions such as walking, lifting, or even involuntary movements like heartbeat.

In contrast, while nerve cells and interneurons are essential components of the nervous system responsible for transmitting signals, they do not produce responses themselves; rather, they relay information. Blood vessels, on the other hand, are involved in circulation and can react to certain stimuli, but they do not generate movement in the way muscle fibers do. This distinction reinforces the role of muscle fibers as direct effectors, making them the correct choice in this context.