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| Mechanism of Olfaction |
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| The nasal passage is lined by the nasal mucosa that have hairs and mucou-secreting cells. The hairs act like filters to remove the dust particles from the inhaled air. The mucous secreted by Bowman's gland keeps the inhaled air moist. The chemicals released by the various odoriferous substances are dissolved in this moisture. Thus, moisture is essential for the perception of smell. |
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| The smell stimulates the receptor cells. Bundles of unmyelinated axons of the olfactory receptors unite to form olfactory nerve, which carry olfactory nerve impulses to the olfactory bulb, a relay station. This in turn conducts the impulses to the olfactory area in the cerebral cortex of the temporal lobe of the cerebral hemisphere through the olfactory nerve. |
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| Olfactory adaptation |
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| When the same odours continuously stimulate the receptors, they become progressively less responsive to the stimulus. Thus, we get used to the smell of a perfume worn by us and others smell it better than us. Olfactory adaptation takes place for unpleasant smell also. The latter becomes more tolerable over a period of time. |
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| In addition to smell receptors, the nose, mouth and tongue contain a network of nerves that form the trigeminal nerve (fifth cranial nerve) also known as Dentists nerve. This nerve reacts to messages of pain. The brain combines the trigeminal signals with those of smell to identify some odours, when exposed to irritants such as ammonia or vinegar. The trigeminal can protect by warning about harmful chemicals in the air. Bowmans glands inside the nose release fluids to get rid of the irritating substances. |
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Nervous Coordination and Integration
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