Receptor, Spinal cord, Effector, Motor neuron, Sensory neuron.

The nervous system detects and responds to changes inside and outside the body.

(i) Receptors are structures at the ends of the nerve fibres that detect chnages in the environment (stimuli), and turn them into electrical impulses. These receptors may be specialised sense organs like aer, eye and skin.

(ii) Sensory neurons carry electrical signals (impulses) from receptors or sense organs to the CNS (Central Nervous System). They are also called afferent neurons.

(iii) The central nervous system consists of the brain and the spinal cord.

(iv) Motor neurons carry impulses from the CNS to effector organs. They are also called efferent neurons.

(v) Effectors are muscles or glands which work in response to the stimulus received from the motor neurons.

Hence the correct order is:

Receptor→Sensory Neuron→Spinal cord→Motor neuron→Effector