Final answer:
Receptor proteins for the sense of smell are situated in the olfactory epithelium of the nasal cavity. They bind to odorant molecules and initiate a signal to the brain,
Step-by-step explanation:
The receptor proteins for the sense of smell, or olfaction, are located within the olfactory epithelium, a small region in the superior part of the nasal cavity. Airborne odorant molecules inhaled through the nose dissolve into the mucus covering this area. These molecules subsequently bind to receptor proteins on the dendrites of bipolar sensory neurons. These specific receptors are known as G protein-coupled receptors, which, upon binding with an odorant-protein complex, initiate a graded membrane potential leading to the perception of smell. The olfactory receptors are part of a complex system that sends signals to the olfactory bulb and then to the brain, allowing us to identify and differentiate an extensive array of odors.
Olfactory receptors occur in large numbers, roughly 12 million in humans, which helps them sense thousands of different smells. This vast array of receptors arises from approximately 400 different genes coding for olfactory receptors, the largest single gene family in the human genome. Compared to other species, such as dogs, who have a broader range of olfactory receptors, humans have a relatively smaller but still remarkably diverse set of these receptors adapted for detecting odors in different environments, contributing to our sense of taste and perceptions of flavor.resulting in the perception of smell. Humans have about 12 million olfactory receptors that can sense a wide variety of odors.