A change you notice in your surroundings is a [ ]; what you do because of it is a [ ].
A change you notice in your surroundings is a receptor; what you do because of it is a response.
A change you notice in your surroundings is a stimulus; what you do because of it is a effector.
A change you notice in your surroundings is a stimulus; what you do because of it is a response.
A change you notice in your surroundings is a response; what you do because of it is a stimulus.