Physiology of Smell and Olfactory Pathway

The olfactory organs are responsible for the olfaction or sense of smell. 

The process of olfaction begins as olfactory cilia capture the odorant molecules.

The odorants bind to the G protein-coupled receptor that can activate the enzyme adenylyl cyclase. The resulting formation of cAMP from ATP opens the sodium channels, causing the influx of sodium ions to depolarize the membrane.

If the depolarization is strong enough to reach the threshold, the resulting nerve impulse is carried through the olfactory axons to the olfactory bulbs.

Here, the axons synapse with mitral cells, forming glomeruli; each glomerulus receives signals from neurons bearing the same types of olfactory receptors.

The mitral cell's axons form the olfactory tracts that carry information to the brain.

Some of these axons carry signals to the frontal lobe for conscious detection and interpretation of odors.

The remaining axons project into the limbic system, which elicits emotional responses to various odors, such as smells associated with danger, pleasure, disgust, or even appetite, and generates appropriate reflexes.