3What is Gustation? Taste , synonyms: smatch or gustation It is one of the five senses.It refers to the ability to detect the flavor of either beneficial (food, nutrition); or detrimental (poisons) chemical substancesSweetness helps to identify energy-rich foods, while bitterness serves as a warning sign of poisons.
4Taste BudsWe perceive tastes through taste cells embedded in taste buds which are embedded in papillae on tongue.
5Where are these buds? There are approximately 100,000 taste buds They are locatedon the back and front of the tongueon the roof, sides and back of the mouthin the throat.
6Tongue Papilla contains hundreds of taste buds Taste buds contain taste 50 – 150 taste cells (they’re not neurons) that have microvilliThe microvilli project out of the pores in the papillaeChemicals binds to the receptors on the microvilli of the taste cells.This information is relayed to the axons of gustatory neurons with which the taste cells synape
7How does taste get into the taste cells? Taste chemicals in food can either pass directly into the taste cells via different channels or bind to surface receptors on the microvilliThe taste cells release neurotransmitters into the synapses between themselves and the axons of the gustatory neuronsThis triggers action potentials in the axons and the info travels to the brain via cranial nerves VII, IX, X
8Information is relayed to the thalamus Information then goes to the primary gustatory cortex (parietal lobe)
9TONGUE MAP MYTHthe 'tongue map' concept which says we have different areas of tongue that senses different tastes, is utterly a false idea This century old misconception comes from the research paper of a German scientist D. P. Hanig published in 1901.in 1974, Virginia Collins found that there are variations in sensitivity to the four basic tastes, but it is too small to have any practical significance.Collins found that all tastes can be detected anywhere there are taste receptors—around the tongue, on the soft palate at back roof of the mouth, and even in the epiglottis, the flap that blocks food from the windpipe.
12How many tastes?The sensation of taste can be categorized into five basic tastes: sweet, bitter, sour, salty, and umami.
13Basic Tastes Taste distribution Most of the tongue is receptive to all basic tastesBut these regions are most sensitive to a given tastea. Bitter across the backb. Sour on side closest to the backc. Salty on side more rostral than sourd. Sweet across front
14Umami? “Umami” is the Japanese word for “meaty” or “savory”. Therefore, it is the taste found in many oriental dishes.The amino acid glutamate produces a strong umami taste.MSG (mono sodium glutamate) has the umami taste
16What’s smell got to do with it? Nasal passages are located in a way that odors can enter through the nose or pharynx and contribute to the perception of flavor
17SMELLY STUFFThere are as many as 100,000 unique odors that we can discriminate80% of which are noxiousOdors perceived to be noxious are often deleterious (rotting meat, etc.).
18Organ of smell The nose is NOT an organ of smell The Olfactory epithelium, located on a thin sheet of cells high up in our nasal cavity is the actual “organ” of smell
19The NeuroepitheliumMade up of ciliated pseudostratified epithelial cellsGoblet cells and mucous glandsOlfactory receptors, which are neurons
20How good is your sense of smell? The size of the olfactory epithelium is proportionate to olfactory acuityMan has 10 cm2 of olfactory epitheliumDog has 170 cm2 of olfactory epitheliumDogs also have 100x as many receptors per cm2 of olfactory epithelium
21Unlike photoreceptors, cochlear hair cells and taste cells, olfactory receptors are actually neurons!They fire action potentialsThey are the only neurons in the nervous system that are replaced regularly throughout life (Every 4-8 weeks)
22Path of Olfaction Odor receptors detect chemicals in air Their axons carry signals towards a fan-like structure, the glomerulusCollectively, these glomeruli compose the olfactory bulb, a brain structure responsible for transmitting scents from odor receptors in the nose to the processing regions of the brain.The olfactory bulb transfers incoming signals from odor receptors into outgoing signals through neurons called mitral cells, that carry odor information up to the cortex via cranial nerve I.In addition to the mitral cells, the olfactory bulb is packed with interneurons and modulatory neurons such as tufted cells, granule cells.There are also glial cells present.
25I ThinkSnot!There are mucus secreting cells at the ends of the olfactory receptorsThis mucus contains cells of the immune system and is shed every ten minutesIndividuals with an infection (cold, flu, etc.) one symptom is a runny noseMucus is shed more frequently to protect the olfactory receptors from infection