A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes.
The ear cannot be identified by any standard structure, nor can it be identified in terms of the stimulus as simply a receiver of sound vibrations. As noted above, mechanical receptor organs will respond to sound vibrations within some region of the frequency range if a sufficiently high level of intensity is provided.
Insula also plays a role in conveying info about sensual touch, pain, temperature, itch, and local oxygen status. Insula is a highly connected relay and thus is involved in numerous functions. Structure. The somatosensory system is spread through all major parts of the vertebrate body.