Answer:
1. Receptor (nociceptor).
2. Afferent neurons.
3. Spinal cord.
4. Motor neurons.
5. Efferent neuron (effector).
Step-by-step explanation:
In Biology, stimulus can be defined as an obvious change in either the chemical or physical structure of an organism' environment (either external or internal). Thus, all living organisms (both animals and plants) respond to changes in their environment and consequently, an appropriate response or reaction is made. Also, stimulus arising from within the organism is known as internal stimulus while those from its environment are known as the external stimulus.
In organisms, the specialized cells that detect stimulus are generally known as sensory receptors while a group of these receptors is referred to as sense organ.
In this scenario, you accidentally stub your toe on a chair when walking in a darkened room. A receptor (nociceptor) relays this information by sensory nerves in the afferent neurons to the spinal cord, which in this case is the spinal cord. You immediately step back because the spinal cord sends a command via the motor neurons to your leg muscles, which are acting as the efferent neuron (effector).