smell sense lab final - The Sense of Smell(olfaction...

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The Sense of Smell (olfaction)IntroductionThe various senses of the body that keep us in touch with what is going on in the external world can be divided into two main groups. One is called the general senses, which consist of the interpretation of temperature, pressure, equilibrium, kinesthetic, umami, and pain receptors of the skin and proprioceptors of muscles and joints. The other group of senses is called special senses, which consist of the interpretation of sight, hearing, taste, touch, and smell.The process of smelling is called olfaction. Olfaction depends upon the interaction between odor stimulus and the olfactory epithelium. This olfactory membrane is a sensitive area, located in the roof of each nasal cavity in humans, is the organ of smell. Thousands of olfactory receptors, receptors for the sense of smell, are located in the epithelium. They can be classified as chemoreceptors because they respond to chemicals in solution brought to them from afar by air or water. The chemicals detected by this system must be small enough to be volatile and dissolve in the mucus of the nose. The olfactory receptor cells are neurons equipped with olfactory hairs, long cilia that protrude from the nasal epithelium and are continuously bathed by a layer of mucus secreted by underlying glands. When the olfactory receptors located on the cilia, receive a stimuli, they are stimulated by chemicals dissolved in mucus, they transmit impulses along the olfactory filaments, which are bundled axons of olfactory neurons that collectively make up the olfactory nerve (cranial nerve I). Axons from the receptor cells lead to and synapse with the olfactory bulb that lies just under the frontal lobe of the brain. Special cells in the bulb are activated by smell stimuli and carry impulses toward the olfactory receptor cells where the impulse is sent to the limbic system, thalamus, and cortex of the brain. There the odor is interpreted, and an “odor snapshot” is made. The olfactory pathways are closely tied into the limbic system (emotional-visceral part of the brain). Thus, olfactory impressions are long-lasting and very much a part of our memories and emotions. The memory of odors is important for several survival functions such as avoiding danger, seeking food, fighting, and mating. Memory of odors is therefore a function of both the limbic structures of the brain and the cerebral cortex.The olfactory neurons tend to adapt rather quickly when they respond to unchanging stimulus, in this case an odor. The rate of adaptation to a particular odor depends upon the concentration of the stimulus and the rate of stimulation. Examples of olfactory adaptation, in everyday life, to the smoking strong odors upon entering a smoker’s house, and after a very short

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