In the simplest arrangement, the receptor-adjustor-effector units form a functional group known as the reflex arc. Sensory cells carry afferent impulses to a central interneuron, which makes contact with a motor neuron. The motor neuron carries efferent impulses to the effector, which produces the response.

a stimulus is detected by a receptor cell, which synapses with a sensory neuron. 
- The sensory neuron carries the impulse from site of the stimulus to the central nervous system (the brain or spinal cord), where it synapses with an interneurone. 
- The interneurone synapses with a motor neuron, which carries the nerve impulse out to an effector, such as a muscle, which responds by contracting. 

The neural path of a reflex is called reflex arc.
1 5 1