Answer: The correct definitions are:
1. Sensory Receptor: The receptor detects the changes that has occurred in the external stimulus. This step is very important as signal would not be transferred further without being received.
2. Integrating Center: The signals is then send to proper areas of the body regarding the stimulus.
3. Effectors: The signals are received by the receptors and respond to the stimulus to maintain the homeostasis in the body of the organism.