Overview
This lecture explains gustation (the sense of taste), its relationship with smell, the structure and function of taste buds, taste transduction, taste pathways, and key taste modalities.
Gustation: The Sense of Taste
- Gustation is the sense of taste, closely linked with the sense of smell.
- The perception of flavor results from the combination of taste and smell.
- Chemo-receptors in taste buds on the tongue detect chemicals in food.
Taste Bud Structure & Types of Taste
- Taste buds are clusters of taste cells located in the papillae (bumps) on the tongue.
- Each taste bud contains multiple types of taste cells to detect different tastes.
- Types of taste detected: sweet (sugars), sour (hydrogen ions/acids), salty (metal ions like sodium), bitter (nitrogen compounds), umami (amino acids/proteins).
- Bitter taste cells are the most sensitive for detecting harmful substances.
- Taste buds also have basal cells (which replace taste cells) and support cells.
Taste Transduction & Signal Transmission
- Chemicals must dissolve in saliva to be detected.
- Taste cells are separate from sensory neurons; they release neurotransmitters to activate these neurons.
- Taste transduction: Chemical binds/bypasses receptor or enters via ion channel, causing depolarization (local potential).
- Local potential opens voltage-gated calcium channels, triggers neurotransmitter release, and initiates an action potential in the sensory neuron.
- Different tastes use different mechanisms: ions (salty/sour) enter directly, others (sweet, bitter, umami) use G-protein-coupled receptors.
Gustatory Neural Pathway
- Taste sensations travel by cranial nerves VII (facial, anterior 2/3 of tongue), IX (glossopharyngeal, posterior 1/3), and X (vagus, pharynx).
- Signals go to the solitary nucleus in the medulla, then the thalamus, then to the primary gustatory cortex in the parietal lobe and insula.
- Taste is also strongly associated with memory and emotion through the limbic system.
Key Terms & Definitions
- Gustation — sense of taste.
- Taste Bud — cluster of taste cells in papillae responsible for detecting taste.
- Papillae — bumps on the tongue lined with taste buds.
- Basal Cells — cells that replace lost or damaged taste cells.
- Transduction — conversion of chemical signals to electrical signals (action potentials) in sensory systems.
- Local Potential — small change in membrane potential in response to stimuli, not an action potential.
- Umami — taste sensation detecting amino acids/proteins.
- Super Taster — person with heightened taste sensitivity, often due to more taste buds.
Action Items / Next Steps
- Complete taste and smell activities at home using available foods (sweet, salty, protein, etc.).
- Prepare for the next lecture on the anatomy and physiology of the eye.