How can humans sense the stimulus? 

Humans can sense the stimulus through their sense organs that act as sensory receptors. The brain distinguishes sensory stimuli through a sensory pathway. 

Action potentials from sensory receptors travel along neurons that are dedicated to a particular stimulus. 

These neurons are dedicated to that particular stimulus and synapse with particular neurons in the brain or spinal cord. Here the information gets processed and the required action is taken.

Hence, the correct option is sensory organs.