Connection Between Smell and Taste: When eating, molecules from food travel from the mouth to the nose, engaging both taste and smell.
Impact of a Stuffy Nose: A cold can block the sense of smell, diminishing taste perception as the sense of taste is less effective alone.
Experiment: Try eating with your nose closed to experience the effect of smell on taste.
Anatomy of the Olfactory System
Nasal Structure:
Nostril: Allows air and odor molecules to enter.
Olfactory Epithelium: Region in the nasal passage responsible for detecting odors.
Cribriform Plate: Bone separating the olfactory epithelium from the brain.
Olfactory Bulb:
Extension of the brain located above the cribriform plate.
Contains nerve bundles, part of the cranial nerves, projecting to the olfactory epithelium.
How Olfaction Works
Sensory Reception:
Olfactory sensory neurons in the epithelium have receptors for specific molecules.
Example: Receptors sensitive to benzene rings, common in aromatic compounds.
Signal Transduction:
Odor molecules bind to receptors on nerve endings.
Binding triggers an action potential (nerve signal) sent to the olfactory bulb.
Glomerulus:
Specific locations in the olfactory bulb where neurons sensitive to the same molecules synapse.
Example: Benzene glomerulus for benzene-sensitive cells.
Mitral/Tufted Cells:
Cells in the glomerulus that project signals to the brain.
Provide an efficient pathway for transmitting odor signals to the brain.
Mechanism of Odor Detection
G Protein-Coupled Receptors (GPCRs):
Odor molecules bind to GPCRs on sensory neurons.
Causes G-proteins to dissociate and trigger a cellular cascade.
Opens ion channels leading to cell depolarization and firing of an action potential.
Pathway to Brain:
Action potential travels through cribriform plate to glomerulus.
Mitral/tufted cells relay signals to the brain, allowing odor perception.
Summary
Key Process: An odor molecule binds to a receptor -> activates a G protein -> opens ion channels -> depolarizes the cell -> fires an action potential -> signal reaches the brain.
Overall Role: The olfactory system enriches taste and is crucial for detecting and interpreting odors.