In a<unk>  system, a<unk>  is a structure that recognizes a stimulus in the internal or external environment of an organism. In response to stimuli the<unk>  initiates<unk>  transduction by creating graded potentials or action potentials in the same cell or in an adjacent one.
Sensory receptor
Receptor 
Nociceptor
Interneuron
Autonomic nervous system
Vestibular system
Circulatory system
Cone cell