Sensory neurons are the nerves which transmit the external stimulus from
the external structures to the brain as chemical impulses, which are
the senses like touch, hearing, taste, vision . . etc.
According to wikipedia:
sensory neurons are neurons that are activated by sensory
input (vision, touch, hearing, etc.), and send projections into the
central nervous system that convey sensory information to the brain or
spinal cord. Unlike neurons of the central nervous system, whose inputs
come from other neurons, sensory neurons are activated by physical
modalities such as light, sound, temperature, chemical stimulation, etc.