Most reflex arcs have five main components: receptors, sensory neurons,interneurons, motor neurone and muscles.Neurons have special proteins called receptors. Receptors respond to signals in the environment like pressure, pain, vibrations, light etc.Sensory neurons have sensory receptors, they get activated by the signal from the environment. The activated sensory neurons extend into spinal cord sending an electrical signal to another neuron, the interneuron.Interneuron then relays the signal to the motor neuron. Motor neuron run out of spinal cord and connect with the muscle or effector.Thus the correct sequence is a sensory receptor, sensory neuron, interneuron, motor neuron and last effector.