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Smell and Taste Senses

Smell and Taste Senses. Chemoreceptors. Respond to chemicals in aqueous solution. Senses of Taste and Smell The chemoreceptors complement one another. Olfaction = Smell. Humans can distinguish some 10,000 or so smells.

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Smell and Taste Senses

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  1. Smell and Taste Senses

  2. Chemoreceptors • Respond to chemicals in aqueous solution. • Senses of Taste and Smell • The chemoreceptors complement one another.

  3. Olfaction = Smell • Humans can distinguish some 10,000 or so smells. • There is thought to be 400 or so smell genes that are active in the nose. • Each gene encodes a unique receptor protein … • However, each of the receptors can respond to several different odors and each odor can bind to several different receptors, and considering most odors a really a complex mixture of many different chemicals, smell is a complicated process.

  4. Activation of Olfactory Receptors • A particular odorant enters the nasal cavity and dissolves in the fluid coating the olfactory epithelium. • When the odorant binds to the olfactory receptor, it causes changes in the membrane opening cation (sodium/calcium) gates to open and if strong enough an action potential to be generated.

  5. The stimulus is then conducted to the olfactory bulb. When the stimulus arrives it moves to a glomerulus, which collect stimulus from like receptor cells, thus one type of odor signal goes to one type of glomerulus. • Mitral cells in the glomerulus refine and amplify the signal and send down olfactory tracts to the olfactory cortex or the hypothalamus/amygdala.

  6. Smells generate several responses in the body • 1. Danger smells such as smoke or skunk scent trigger flight of fight reponse. • 2. Appetizing smells trigger saliva and the digestive tract. • 3. Unpleasant odors can trigger reflex responses such as choking or coughing.

  7. Taste • Most of our 10,000 taste buds are on the tongue, but some are scattered throughout the mouth cavity. • Taste buds are found in structures called papillae on the tongue. • Each taste bud has two major types of cells: gustatory (taste) or basal cells.

  8. Gustatory hairs project from gustatory cells and these hairs have the chemoreceptors on them. • Basal cells act as basic stem cells replacing the gustatory cells. • Due to the busy/damaging nature of eating etc. gustatory cells are replaced on average every 7-10 days. So if you burn your tongue on hot food ….

  9. Five Basic Tasts • Salty • Sweet • Sour • Bitter • Umami ???? Yes! Steak Yum! • And a possible 6th???????

  10. Activation of Taste Receptors • For a chemical to be tasted it has to be dissolved in saliva. • The dissolved chemical contacts the gustatory hair and induces a graded depolariztation, which causes the release of a neurotransmitter from a synaptic vesicle in the gustatory cell. • Different gustatory cells have different thresholds for activation.

  11. Release of the neurotransmitter may generate an action potential . • The impulses are sent via different cranial nerves to the brain (gustatory cortex in the insula lobe, hypothalamus, and thalamus, and even pass through the medulla on the way.

  12. Other About Taste • 80% of taste is really from smell. • There are also thermoreceptors in the mouth. • Hot/Spicy foods like chili peppers actually excite pain receptors which can bring about a pleasurable effect. • An important role of taste is to trigger a reflexes involved in digestion.

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