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Biology LibreTexts

Part 5: Taste

  • Page ID
    20779
  • Taste involves stimulation of receptor proteins on gustatory cells within taste buds. The perceived sensations correspond to common chemicals: Salty (Na+), Sweet (disaccharides, e.g. sucrose), Bitter (various, common test is Ca2+), sour (H+), and umami (glutamate). Also, taste is often integrated as a perception with olfactory sensory input.

    Anatomy & Physiology: Taste buds are arranged along the tongue epithelium. Sensory epithelial cells release neurotransmitter signal molecules to sensory neurons of cranial nerves. Information is integrated along the brain stem and in the temporal cortex.

    Taste.PNG

    Figure \(\PageIndex{1}\) The tongue is covered with small bumps, called papillae, which contain taste buds that are sensitive to chemicals in ingested food or drink. Different types of papillae are found in different regions of the tongue. The taste buds contain specialized gustatory receptor cells that respond to chemical stimuli dissolved in the saliva. These receptor cells activate sensory neurons that are part of the facial and glossopharyngeal nerves. LM × 1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

    Specimens & Models for examination: Histology slide of tongue/taste buds

    Physiology: Taste can be identified using solutions of chemicals known to stimulate distinct receptor proteins. Solutions can be prepared from common ingredients to test for sensitivity.

    5A: Histology Exploration

    Use a microscope to explore the cellular aspect of a taste bud. Find an individual taste bud and draw it. Can you label any structures if you use the above diagram as a guide?

    5B: PTC Test

    One bitter taste receptor protein is encoded by the PTC gene, or TAS2R38 (discovered in 2003). There are at least 30 different genes coding for bitter taste receptors. Phenylthiocarbamide (PTC), also known as phenylthiourea (PTU), is only detected by ~70% of the population on average. Tasting PTC is correlated with the dominant genotype.

    Directions:

    PTC tasting test kits provide material to survey the class. Testing is a simple positive response for bitter taste, while non-tasters will report no taste. 

    After placing the strip on your tongue do you taste anything? Yes or no?

    If you answered YES!, then you have the dominant genotype for the PTC gene!

    5C: Taste Threshold Test

    Similar to the olfaction tests, serial dilutions of basic chemicals can be used to test for variable sensitivity in subjects. Sucrose and NaCl are common tests for sweet and salty. Serial solutions can be applied with cotton swabs to the subjects tongue to test for sensitivity. Similar to the smell test, list the concentrations of the two substances and circle the one where you can begin to taste the substance.

    Do you and your lab partner vary in your sensitivities? If you differ, then provide a possible explanation as to why.

    • HISTORICAL NOTE: The ‘standard’ map of taste buds common in many lab manuals has been disproved by subsequent research (J. Cell Biology, 2010 vol. 190 no. 3 285-296  doi: 10.1083/jcb.201003144). There is more variability among individuals than accounted for by the original 1942 map (not shown, intentionally).
    • Individuals can map their tongues for taste buds, once sensitivity thresholds have been determined.