co40 - CHAPTER 40 SENSE ORGANS Chapter Outline 40.1...

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CHAPTER 40 S ENSE O RGANS Chapter Outline 40.1 Chemical Senses A. Chemoreceptors are responsible for taste and smell by being sensitive to chemicals in food, liquids, and air. 1. Chemoreception is found universally in animals; it is thought to be the most primitive sense. 2. Chemoreceptors are present all over a planarian but concentrated in the auricles at the side of the head. 3. Insects, such as houseflies, taste with their feet. 4. Crustacea have chemoreceptors on their antennae and appendages. 5. In amphibians, chemoreceptors are located in the nose, mouth, and all over the skin. 6. In mammals, receptors for taste are in the mouth, and receptors for smell are in the nose. B. Sense of Taste 1. Human taste buds are located primarily on the tongue. 2. Many lie along the walls of papillae , the small elevations on surface of the tongue. 3. Isolated ones are present on the surfaces of the hard palate, pharynx, and epiglottis. 4. Taste buds are embedded in tongue epithelium and open at a taste pore. 5. Taste buds have supporting cells and elongated taste cells that end in microvilli . 6. Microvilli bear receptor proteins for certain chemicals. a. Molecules bind to receptor proteins and impulses are generated in associated sensory nerves b. Nerve impulses go to the brain cortical areas which interpret them as tastes. 7. Humans have four primary types of taste buds. a. Taste buds for each are concentrated in particular regions. 1) Sweet receptors are most plentiful near the tip of the tongue. 2) Sour receptors occur primarily along the margins of the tongue. 3) Salty receptors are most common on the tip and upper front portion. 4) Bitter receptors are located near the back of the tongue. b. The brain appears to take an overall weighted average of taste messages as the perceived taste. C. Sense of Smell 1. The sense of smell depends on olfactory cells located in olfactory epithelium high in the roof of the nasal cavity. 2. Olfactory cells are modified neurons. 3. Each cell has a tuft of five olfactory cilia that bear receptor proteins for an odor molecule. a. There are around 1,000 different types of odor receptors; many olfactory cells carry the same type. b. Nerve fibers from like olfactory cells lead to the same neuron in the olfactory bulb. b. An odor activates a characteristic combination of cells; this information is pooled in the olfactory bulb. c. Interneurons communicate this information via the olfactory tract to areas of cerebral cortex. 4. Olfactory bulbs are directly connected with the limbic system; smells associate with emotions and memory. 5. Taste and smell supplement each other. a. “Smelling” food also involves the taste receptors. b. Losing taste when you have a cold is usually due to a loss of smell. 40.2
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This note was uploaded on 10/24/2009 for the course BIO 172 taught by Professor Clark during the Fall '08 term at University of Michigan.

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co40 - CHAPTER 40 SENSE ORGANS Chapter Outline 40.1...

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