The special senses - Taste

Taste

1. The Special Senses: Taste Dr. Binu Babu Ph. D (N), MSN, MBA Mrs. Jincy Ealias MSN, RN

2. Taste The word taste comes from the Latin taxare , meaning “to touch, estimate , or judge.” Most of the 10,000 or so taste buds are found on the tongue There are five basic taste sensations Sweet – sugars, saccharin, alcohol, and some amino acids Salt – metal ions Sour – hydrogen ions Bitter – alkaloids such as quinine and nicotine Umami – elicited by the amino acid glutamate

3. Taste buds Taste buds are found in papillae of the tongue mucosa Papillae come in three types: filiform, fungiform, and circumvallate. Fungiform and circumvallate papillae contain taste buds. Each flask-shaped taste bud consists of 50 to 100 epithelial cells of two major types: Gustatory epithelial cells Basal epithelial cells

4. The gustatory epithelial cells are the receptor cells for taste the taste cells. Long microvilli called gustatory hairs project from the tips of all gustatory epithelial cells and extend through a taste pore. Basal Epithelial Cells: This taste bud cells are subjected to friction and are routinely burned by hot foods. They are among the most dynamic cells in the body, and they are replaced every seven to ten days

5. Papillae Vallate (circumvallate) papillae:- form an inverted V-shaped row at the back of the tongue. Each of these papillae houses 100–30 taste buds. Fungiform papillae are mushroom-shaped elevations scattered over the entire surface of the tongue that contain about five taste buds each. Foliate papillae are located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood . The entire surface of the tongue has filiform papillae. These pointed, threadlike structures contain tactile receptors but no taste buds. They increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity.

6. Structure of Taste Buds

7. Intrinsic Muscles Superior longitudinal muscle: Lies beneath mucous membrane Shortens the tongue, make its dorsum concave Inferior longitudinal muscle: lying close to the inferior surface of the tongue between genioglossus and hyoglossus shortens the tongue, make its dorsum convex Transverse muscle: extends from median septum to the margins makes the tongue narrow and elongated Vertical muscle: found at the borders of the anterior part of the tongue makes the tongue broad and flattened

8. Extrinsic Muscles Genioglossus : origin : Upper genial tubercle of mandible insertion : the fibres radiate widely to be inserted into the mucous membrane of the tongue; the lowest fibres passing down to the hyoid body Hyoglossus : origin : from the length of the greater horn of the hyoid bone and from lateral part of its body insertion : the fibres extend upward and its upper border interdigitating at right angles with the fibres of styloglossus , and is attached to the side of the tongue Styloglossus : origin: from the front of the lower part of the styloid process and the upper part of the stylohyoid ligament Palatoglossus : origin : arises from the undersurface of the palatine aponeurosis insertion : side of the tongue 

9. Blood Supply and Venous Drainage Tongue is supplied by the lingual artery Drained through lingual vein

10. Physiology of Gustation Chemicals that stimulate gustatory receptor cells are known as tastants . Taste Transduction: Three different mechanisms underlie how we taste. Salty taste is due to Na + influx through Na + channels, which directly depolarizes gustatory epithelial cells. Sour is mediated by H + , which acts intracellularly to open channels that allow other cations to enter. Bitter , sweet, and umami responses share a common mechanism, but each occurs in a different cell. Each taste’s unique set of receptors is coupled to a common G protein called gustducin . Activation leads to the release of Ca 2+ from intracellular stores , which causes cation channels in the plasma membrane to open, thereby depolarizing the cell and releasing the neurotransmitter ATP.

11. The Gustatory Pathway

12. References Tortora , Gerard J, and Bryan Derrickson .  Principles of Anatomy and Physiology . 2nd ed., Milton, Qld , John Wiley & Sons Australia, Ltd, 2019 . Garg , Krishna, and Medha Joshi.  Anatomy and Physiology for Nurses . New Delhi, Cbs Publishers & Distributors Pvt. Ltd, 2015. Kendall , Elward , et al.  Anatomy and Physiology . Lincolnwood, Ill., Ntc Learning Works, 1998 . Scanlon, Valerie C, and Tina Sanders.  Essentials of Anatomy and Physiology . Philadelphia, Pa, F.A. Davis Co, 2011.

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