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After studying this chapter, you should be able to:
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Describe the basic features of the neural elements in the olfactory epithelium and olfactory bulb.
Describe signal transduction in odorant receptors.
Outline the pathway by which impulses generated in the olfactory epithelium reach the olfactory cortex.
Describe the location and cellular composition of taste buds.
Name the five major taste receptors and signal transduction mechanisms in these receptors.
Outline the pathways by which impulses generated in taste receptors reach the insular cortex.
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Smell (olfaction) and taste (gustation) are generally classified as visceral senses because of their close association with gastrointestinal function. Physiologically, they are related to each other. The flavors of various foods are in large part a combination of their taste and smell. Consequently, food may taste “different” if one has a cold that depresses the sense of smell. Both smell and taste receptors are chemoreceptors that are stimulated by molecules in solution in mucus in the nose and saliva in the mouth. Because stimuli arrive from an external source, they are also classified as exteroceptors. The sensations of smell and taste allow individuals to distinguish between estimates of up to 30 million compounds that are present in food, predators, and mates and to convert the information received into appropriate behaviors.
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OLFACTORY EPITHELIUM AND OLFACTORY BULBS
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Olfactory sensory neurons are located in a specialized portion of the nasal mucosa, the yellowish pigmented olfactory epithelium. In dogs and other animals in which the sense of smell is highly developed (macrosmatic animals), the area covered by this membrane is large; in microsmatic animals, such as humans, it is small. In humans, it covers an area of 10 cm2 in the roof of the nasal cavity near the septum (Figure 11–1). The olfactory epithelium is said to be the place in the body where the nervous system is closest to the external world.
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