Olfactory System and Odor Detection

How We Detect Odors

• Smelling something pleasant or unpleasant depends on how far away the source is.
• Some strong odors, like lilacs or vinegar, can be detected even when far from the source.
• Detecting smells from a distance relates to the movement of molecules from the source to the nose.
• This is similar to evaporation: Water molecules separate from the water and become water vapor.
• Molecules of substances (like those in the odor) also evaporate and move into the air, eventually reaching the nose.
• The nose detects specific molecules.
• When these molecules reach the nose, they dissolve in mucus.
• Olfactory epithelium, beneath the mucus, contains receptors that detect odors.

Olfactory Receptors

• Receptors are like locks, and odor molecules are like keys.
• One receptor can be activated by multiple odor molecules, and one odor molecule can activate multiple receptors.
• Molecules of similar shape generally trigger similar sensations.
• The brain processes signals from olfactory receptors.
• Similar past experiences with similar odors help categorize and identify them.

Odor Molecules and Receptors

• Different molecules have different shapes and structures.
• Some molecules don't trigger responses due to their shape incompatibility with receptors.
• A scent is often composed of a mixture of different molecules, each targeting unique receptors.
• Signals from multiple activated receptors simultaneously are sent to the brain, allowing us to identify complex and blended smells (e.g., lavender's unique smell being a combination of linalool and linalyl acetate.)

Number of Detectable Odors

• Scientists estimate a person can detect around 1 trillion different odors.