THE SENSE OF SMELL1 Smell is the most direct of all the senses. It is thought to be the oldest sense in terms of human evolution, which may explain why smell is hard—wired into the brain. The olfactory nerve, which manages the perception of smells, is essentially an extension of the brain. The olfactory nerve provides a direct link from receptors at the top of the nose to the portion of the brain that controls memory, emotion, and behavior. 2 The olfactory system detects certain airborne chemicals that enter the nose and then transmits this chemical information to the limbic system in the brain. The olfactory region at the upper end of each nostril is yellow, moist, and full of fatty substances. The shade of yellow indicates the strength of the sense of smell: the deeper the shade, the keener and more acute it is. Animals have a very strong sense of smell, so their olfactory regions are dark yellow to reddish brown, while those of humans are light yellow. 3 When an odorous substance enters the nose, it binds to olfactory receptor cells, the neurons lining the yellow upper portion of the nasal cavity. Olfactory receptor cells contain microscopic hairs called cilia that extend into the layer of mucus coating the inside of the nose. Odor molecules diffuse into this region and are absorbed by the cilia of the olfactory receptor cells. What this means is that when we hold a rose to our nose and inhale, odor molecules float up into the nasal cavity, where they are absorbed by five million olfactory receptor cells. The receptor cells alert the olfactory nerve, which sends impulses to the brain’s olfactory bulb, or smell center. Thus, olfactory information about the rose enters the brain’s limbic system, where, in most of us, it stimulates a feeling of pleasure. 4 The limbic system of the brain integrates memory, emotion, and behavior. The system is composed of a group of related nervous system structures that are the functional center of emotions such as anger, fear, pleasure, and sadness. The components of the limbic system are linked to the cerebral cortex, the part of the brain involved in complex learning, reasoning, and personality. The cerebral cortex makes decisions about the emotional content of these unique human qualities after “consulting” the limbic system and other brain centers in processing and retrieving memories. It may, in turn, use memories to modify behavior. 5 Scent may be the strongest trigger of memory and emotions. When we inhale a scent, receptors in the brain’s limbic center compare the odor entering our nose to odors stored in our memory. Along the way, memories associated with those odors are stimulated. A smell can be overwhelmingly nostalgic because it triggers powerful images and emotions. The waxy fragrance of crayons can instantly transport us to our second-grade classroom, or the scent of freshly mown grass can flood us with the joy of summer freedom. What we see and hear may fade quickly in short- term memory, but what we smell is sent directly to long-term memory. 6 Smells can increase alertness and stimulate learning and retention. In one study, children memorized a word list, which was presented both with and without accompanying scents. The children recalled words on the list more easily and with higher accuracy when the list was given with scents than without, showing the link between smell and the ability to retain information. In another study, researchers examined how various smells can increase alertness and decrease stress. They found that the scent of lavender could wake up the metabolism and make people more alert. They also found that the smell of spiced apples could reduce blood pressure and avert a panic attack in people under stress. Glossary: nostalgic: causing a desire for things, persons, or situations of the past; causing homesickness retention: the act of retaining: keeping, holding, or maintaining 26. Why does the author use the term hard-wired in describing the sense of smell and the brain? (A) To describe the texture and feel of the olfactory nerve (B) To emphasize the close connection between smell and the brain (C) To compare the power of smell with that of other senses (D) To explain bow the sense of smell evolved in early humans 27. The word detects in paragraph 2 is closest in meaning to (A) notices (B) destroys (C) fights (D) compares 28. Of what significance is the color of the olfactory region at the upper end of each nostril? (A) The color changes with different airborne chemicals. (B) The significance of the color is little understood. (C) The color becomes darker when an odor is present. (D) The color shows the strength of the ability to smell. 29. The word diffuse in paragraph 3 is closest in meaning to (A) drop (B) flow (C) cut (D) bend 30. What happens when the cilia of the olfactory receptor cells absorb odor molecules? (A) The tiny hairs inside the nose become darker in color. (B) The nervous system activates the digestive system. (C) The olfactory nerve sends impulses to the brain. (D) Some receptor ceils die and are replaced by new cells. 31. The word integrates in paragraph 4 is closest in meaning to (A) predicts (B) connects (C) damages (D) slows 32. When a scent is inhaled, all of the following occur in the limbic system EXCEPT (A) The scent is compared to other scents stored in memory. (B) The scent is transmitted to the other sensory organs. (C) The brain stimulates memories associated with the scents. (D) The person may feel an emotion related to a memory. 33. Why does the author mention crayons and freshly mown grass in paragraph 5? (A) To give examples of smells that can trigger memories and emotions (B) To compare typical responses to two common smells (C) To explain why smells are likely to a fleet a person’s behavior (D) To identify smells that can increase alertness and work efficiency 34. The word which in paragraph 6 refers to (A) learning (B) study (C) list (D) smell 35. What can be inferred from paragraph 6 about learning? (A) Learning cannot take place unless all of the senses are stimulated. (B) Scents can strengthen the ability to hold new information in the memory. (C) It is easier to recall previous learning than it is to retain new information. (D) Children will not learn much if they are distracted by offensive odors.