Final answer:
Negative feedback is a biological process where a response to a stimulus decreases function, maintaining homeostasis and preventing overactivity in systems such as hormonal regulation, muscle use, and immune response.
Step-by-step explanation:
When a stimulus elicits a response that leads to a decrease in function within biological systems, this process is known as negative feedback. This is a common mechanism in biology that helps maintain homeostasis or the stability of a system's internal environment. For instance, down-regulation is where high hormone levels lead to a reduced number of hormone receptors, which in turn can decrease the hormone's effect on the body, preventing overactivity. Similarly, atrophy is the decrease in the size of a muscle due to nonuse, effectively reducing its function over time in response to a lack of stimulus.
Extinction in classical conditioning also reflects this concept—at the point where a conditioned stimulus is no longer paired with an unconditioned stimulus, the learned response begins to decrease and eventually disappears. In another example, immunosuppression causes a decreased effectiveness of the immune system, often leading to an increased susceptibility to infections, as seen in cases like AIDS.
Negative feedback mechanisms are crucial for preventing overreaction within biological systems and ensuring that functions do not exceed their necessary limits, thus maintaining overall system equilibrium.