How Smell Works: Olfaction Explained from Nasal Cavity to Brain

Correction: Olfaction (sense of smell) occurs in the nasal cavity, not in the lungs, alveoli, or bronchioles.

The Olfactory Pathway

1. Odorants (volatile molecules) enter nasal passages with inspired air
2. They dissolve in mucus covering the olfactory epithelium (superior nasal concha & septum)
3. Olfactory receptor neurons (bipolar) express specific G-protein-coupled receptors (~400 types in humans)
4. Binding → cAMP cascade → depolarization → action potentials
5. Axons (CN I) traverse cribriform plate → olfactory bulb (glomeruli) → olfactory cortex (piriform cortex, amygdala, entorhinal cortex) → conscious perception & emotional memory

Key Features

• Direct limbic connection → strong emotional/evocative memories
• Rapid adaptation (receptor desensitization)
• Humans distinguish ~1 trillion odor mixtures

Respiratory mucosa in lower airways has chemoreceptors (irritant detection, cough reflex) but no olfactory function.