Olfactory receptors exist throughout the human nasal cavity but mainly olfactory region. They are direct nerve endings of the 1st cranial nerve, the olfactory nerve on left and right side. The cranial nerve actually is a cluster of small fibers from frontal lobe running down the sieve like ethmoid bone. They are well developed in lower animals like dogs. Humans use less of odor sense that's why olfactory sense and nerves are not well developed. I hope this is the answer that you were looking for.