Final answer:
The sense of smell, or olfaction, begins with the inhalation of odor molecules that dissolve in the olfactory epithelium, initiating a response in the olfactory receptors. These receptors transmit signals to the olfactory bulb, which then sends information to various brain regions for the perception of smell. Humans have about 350 olfactory receptors types, allowing them to detect numerous odors.
Step-by-step explanation:
Pathway of Smelling
The process of smelling, or olfaction, begins when odorant molecules enter the nose and dissolve in the olfactory epithelium, which is the mucosa at the back of the nasal cavity. Olfactory receptor neurons located here, each with dendrites extending into the mucus lining, respond to these molecules. Olfactory receptors are G protein-coupled and initiate a graded membrane potential leading to action potentials.
Odor receptors and their associated nerves line the top of the nasal passages and transmit information directly to the olfactory bulb in the brain. The olfactory bulb is organized into neural clusters called glomeruli, with each glomerulus specific to one odorant. Signals from the glomeruli are then sent to various parts of the olfactory system including the olfactory cortex, frontal cortex, thalamus, amygdala, hypothalamus, and temporal lobe structures associated with memory and emotions, leading to the perception of smell.
Humans have a diverse range of olfactory receptors, about 350 types, allowing them to sense approximately 10,000 different odors. These receptors work in combinations to detect a wide array of smells. The sense of taste is closely linked to olfaction, as both involve molecules stimulating specific chemoreceptors.