Chapter 7 The Sensory Systems 285 © Body Scientific International Figure 7.18 The olfactory region. Which labeled part of drawing B is covered with mucus when you have a cold? Why does this affect your sense of taste? Olfactory region Olfactory epithelium Olfactory bulb Bone Olfactory nerve Mucous layer Olfactory filaments of the olfactory nerve Supporting cell Olfactory receptor cell Olfactory hairs Odor molecules Nasal cavity The development of the nose and nasal cavities is most active between the fourth and seventh weeks of pregnancy. The nostrils appear a few weeks later. By 10 weeks, the olfactory receptor cells have formed, and the developing fetus can now become familiar with the scent of the mother’s amniotic fluid. Newborn infants have a highly sensitive sense of smell. They form strong associations between specific scents and related experiences. They also use scents to identify people—especially those who are familiar, such as parents or other caretakers. During the first year babies also rely heavily on odors to identify foods they like and dislike. The ability to differentiate odors continues to develop through about age eight. The nose and nasal passages are fully formed at birth but continue to grow in proportion to skeletal growth. Sagittal plane growth and anterior projection of the nose continue to increase in females until age 12 to 16 and to increase in males until age 18 and sometimes beyond. During the growth period, the angular shapes and positional relationships of the nose, lips and chin remain relatively constant in both genders. Generally, males have larger noses than females. The nose continues to grow and change during life, with increasing nasal volume and nostril area. By the age of approximately 30, nose growth has slowed. Between 50 and 60 years of age, nasal volume in men increases by about another 29 percent and by about another 18 percent in women. With advancing age, the cartilage and skin of the nose lose strength, resulting in sagging of the nose. After age 60, loss of olfactory receptor cells may contribute to a diminished sense of smell, resulting in the inability to detect odors in low concentrations. Life Span Review 1. At what point is the developing fetus able to smell? 2. At what age is the sense of smell fully developed? 3. What changes are characteristic of the nose and sense of smell with advanced age? LIFE SPAN DEVELOPMENT: The Nose and Sense of Smell Copyright Goodheart-Willcox Co., Inc.