Our Versatile Sense of Smell
STIRS UP MEMORIES, ENHANCES TASTES
WHAT is your favorite aroma? When this question was asked of several people, their answers were fascinating. Bacon frying. Salt air off the ocean. Clean laundry blowing in the wind. Freshly mowed hay. Hot spices. Puppy breath. When probed further as to why these were their favorite smells, all had a specific, vivid memory that they recalled with the first whiff of the odor. Very often the memories were from childhood.
A young woman remembers lying in her bed in the morning, the tantalizing aroma of frying bacon drifting into the room, beckoning her to breakfast with her family.
Louise, 58, said that the fragrance of sea air brings back her childhood summers on the coast of Maine in the United States. “The freedom we had,” she says, “running and playing in the sand, digging for clams and cooking them over an open fire!”
Michele, 72, remembers the times as a child when she helped her mother gather the laundry off the clothesline, burying her face in armloads of it as she carried it into the house, breathing deeply to take in the fresh, clean fragrance.
Freshly mowed hay spreads the scent that takes Jeremy back 55 years, to his days as a child on an Iowa farm, riding on a wagonload of freshly cut hay being taken into the barn to escape the rain he and his father could smell coming.
“Hot spices” was the response of 76-year-old Jessie, who closed her eyes and told of her family cooking apple butter (a heavily spiced sort of jam made in the United States) in an iron kettle outdoors. Seventy years ago, but the memory was still very much alive.
Carol remembers the cuddly little puppy she held in her lap when she was five and recalls the smell of the puppy’s breath. Ah, yes, that smell gives her the feeling of being warm in the sunshine on an old front porch in a little seersucker dress.
Now, what about you? Has a smell ever pleased you as it has others—evoking memories, stirring emotions? Have you ever felt invigorated by pine-scented mountain air or refreshed by the tangy stimulus of a sea breeze? Or perhaps you’ve found your mouth watering after catching a stray whiff from a bakery shop. Neuroscientist Gordon Shepherd stated in National Geographic: “We think our lives are dominated by our visual sense, but the closer you get to dinner, the more you realize how much your real pleasure in life is tied to smell.”
Smell does wonders for our sense of taste. While taste buds differentiate between the salty, the sweet, the bitter, and the sour, our sense of smell picks up other, subtler elements of flavor. If they lacked a smell, apples and onions might taste virtually the same. Or, for example, see how much flavor a piece of chocolate loses when you eat it while holding your nose.
Picture an appetizing piece of food—let’s say a freshly baked pie. Those enticing aromas waft up from it because it is releasing molecules and setting them adrift in the air currents. Along comes your nose, sniffing away eagerly. It sucks in air and sends those molecules on their way through the amazing machinery of our sense of smell.
For a more detailed examination of the process of olfaction, see the box on pages 24 and 25. The intricacy and complexity of this sense is truly awe-inspiring.
Odors and Their Effects on You
Perfumers, master chefs, and vintners have for centuries recognized the power of aromas to captivate the mind and please the senses. Today, fragrance psychologists and biochemists are trying to tap the power of scent in new ways. Experimenting with fragrances ranging from lily of the valley to apple and spice, odor engineers have pumped scents into schools, office buildings, nursing homes, and even a subway train in order to study effects on the mind and human behavior. They claim that certain scents can affect moods, making people friendlier, improving their efficiency in the workplace, and even enhancing mental alertness.
According to The Futurist magazine, people line up at a fashionable health club in Tokyo, Japan, for a 30-minute “aroma cocktail” said to relieve the stress of city living. Japanese scientists have also studied the effects of forest air on humans and recommend walking through forests as a remedy for jangled nerves. The terpenes (pine scent) that trees exude have been found to relax not simply the body but especially the mind.
Not all odors are healthful; far from it. What delights one person might well make another miserable. Strong odors, even of perfumes, have long been known to aggravate asthma and trigger allergic reactions in some people. Then, too, there are the malodors that everyone agrees on—noxious fumes spewed from industrial smokestacks and motor vehicle exhaust pipes, rancid odors of garbage landfills and sewage basins, and vapors from volatile chemicals used in many industrial workplaces.
Of course, dangerous chemicals occur naturally in our environment but are usually so diffuse as to be harmless. However, when such chemicals are highly concentrated, overexposure to them can cause even the resilient olfactory nerve cells to degenerate. For instance, solvents such as those used in paints, as well as many other industrial chemicals, have been listed by experts as hazardous to the olfactory system. There are also physical disorders that can impede or destroy the sense of smell.
Do You Value the Gift?
Surely the sense of smell is worth protecting from such threats wherever possible. So familiarize yourself with the hazards of any chemicals you must work with, and take whatever reasonable precautions are necessary to protect your sensitive olfactory system. (Compare 2 Corinthians 7:1.) On the other hand, it is good to be equally concerned about the sensitivities of others. A high standard of cleanliness, including our homes and our bodies, can do much in this regard. Some have also chosen to be extra cautious with the use of perfumes—especially when they plan to be in close proximity with many others for some time, as in a theater or an Assembly Hall.—Compare Matthew 7:12.
In general, though, the olfactory system is a low-maintenance gift. It asks little of us in the way of care and protection, yet it brings us a daily bounty of small pleasures in life. When you receive a gift that makes you happy, do you feel a desire to thank the giver? Millions of people today earnestly thank the Creator for the marvelous way in which the human body is made. (Compare Psalm 139:14.) We might well hope that more such thanks and praise ascend to him and, like the sacrifices of the ancient Israelites, be as “a restful odor” to our loving, generous Creator.—Numbers 15:3; Hebrews 13:15.
[Box/Diagram on page 24, 25]
How the Sense of Smell Works
First, the Odor Is Detected
ODORS enter the nasal passages when you breathe in. Also, when you swallow food, molecules are forced up the back of the mouth and into the nasal cavity. First, though, odorous air has to make it past the “guards.” Lining the nostrils are the trigeminal nerves (1), which trigger sneezing when they sense stinging or irritating chemicals. These nerves also give pleasure by reacting to the pungency of some flavors.
Next, odorous molecules are pushed upward by eddies that form when air currents swirl around three bony, scroll-like protrusions called turbinates (2). The airstream, moistened and warmed along the way, carries the molecules to the epithelium (3), the primary reception area. Situated in a narrow channel high up in the nose, this thumbnail-size patch of tissue is packed with some ten million sensory neurons (4), each tipped with numerous hairlike projections, called cilia, bathed in a thin layer of mucus. So sensitive is the epithelium that it can detect 1/1,300,000,000 ounce [1/460,000,000 mg] of certain odorants in a single whiff of air.
But exactly how odors are detected is still shrouded in mystery. After all, humans can distinguish as many as 10,000 odors. And there are more than 400,000 odorous substances in our environment, with chemists constantly creating new ones. So how does our nose make sense of all this olfactory hubbub? Well over 20 different theories attempt to explain the mystery.
Just recently scientists have made progress toward solving part of this puzzle. Some evidence was found in 1991 that there are tiny proteins, called olfactory receptors, woven through the cell membranes in the cilia. Apparently such receptors bind differently to differing types of odorous molecules, thus giving each odor a distinctive “fingerprint.”
Second, the Odor Is Transmitted
To pass this information along to the brain, coded electrochemical messages are fired along the olfactory neurons (4). Dr. Lewis Thomas, a science essayist, calls these neurons the ‘Fifth wonder of the modern world.’ They are the only primary nerve cells that replicate every several weeks. Also, they have no protective barrier between them and the surrounding stimuli, as do the sensory nerve cells that lurk protected within the eye and the ear. Instead, the olfactory nerves reach out from the brain itself and come into direct contact with the outside world. Thus, the nose is a meeting place of brain and environment.
These neurons all lead to the same destination: the twin olfactory bulbs (5) on the underside of the brain. These bulbs are the main relay station to other parts of the brain. First, though, they edit the flood of olfactory information, eliminate all but the essential, and then send it on.
Third, the Odor Is Perceived
The olfactory bulbs are intricately “wired” into the brain’s limbic system (6), an elegantly looping set of structures that plays a key role in storing memories and in triggering emotional reactions. This is where “the cold world of reality is transformed into a bubbling caldron of human feelings,” according to the book The Human Body. The limbic system is so extensively tied in with the sense of smell that it was long referred to as the rhinencephalon, meaning “nose brain.” This close link between nose and limbic system may explain why we react so emotionally and nostalgically to odors. Aha! The frying bacon! The clean laundry! The freshly mowed hay! The puppy breath!
Depending on the odor sensed, the limbic system may activate the hypothalamus (7), which in turn may direct the brain’s master gland, the pituitary (8), to produce various hormones—for instance, those hormones that control appetite or sexual function. No wonder, then, that the odor of food can suddenly make us feel hungry or that a perfume can be seen as an important factor in sexual attraction.
The limbic system also reaches into the neocortex (9), a rather intellectual, analytical neighborhood within the brain. Here is where news from the nose may be compared with input coming in from the other senses. In an instant, you might combine such data as an acrid odor, a crackling sound, and a faint haze hanging in the air to form a conclusion—fire!
The thalamus (10) plays a role too, perhaps mediating between those very different parts, the “emotional” limbic system and the “intellectual” neocortex. The olfactory cortex (11) helps to distinguish between similar odors. Various brain parts can also send messages back to the transmission stations, the olfactory bulbs. Why? So that the bulbs can then modify the perception of odors, in effect turning them down or even turning them off.
You may have noticed that food doesn’t smell as inviting when your appetite is sated. Or have you ever been subjected to a pervasive, inescapable odor that seemed to fade away with time? The olfactory bulbs, informed by the brain, bring about these changes. They may be assisted by the receptor cells on the cilia, which are said to fatigue easily. This is a helpful feature, especially in the face of potent foul odors.
Quite a system, isn’t it? Yet, we have barely touched on it! Entire books have been devoted to this intricate and sophisticated sensory system.
[Box on page 26]
Millions of people suffer smell dysfunction. The fragrance of springtime or of flavorful food does little or nothing for them. One woman described her sudden complete loss of smell this way: “We all know about blindness and deafness, and certainly I would never trade my disability for those afflictions. Yet we so take for granted the rich aroma of coffee and sweet flavor of oranges that when we lose these senses, it is almost as if we have forgotten how to breathe.”—Newsweek magazine.
Smell disorders can even be life-threatening. A woman named Eva explains: “Not being able to smell, I have to be very careful. I shudder to think of winter coming, because I must close all the windows and doors to my apartment. Without the fresh air, I could easily be overcome by gas fumes if the pilot light went out on the gas stove.”
What causes smell dysfunction? While there are over a score of causes, three are most common: head injury, upper respiratory viral infection, and sinus disease. If the nerve pathways are severed, if the epithelium is rendered insensitive, or if air cannot reach the epithelium because of blockage or inflammation, the sense of smell vanishes. Recognizing such disorders as a major problem, clinical research centers for the study of taste and smell have been established.
In an interview, Dr. Maxwell Mozell of the State University of New York Health and Science Center at Syracuse related: “We’ve had patients in here that [smell a bad odor perceived only by themselves]. They smell horrible things. One woman smelled fish all the time. Imagine if every minute of every day, you smelled fish or burning rubber.” After suffering for 11 years with an unpleasant odor in her nose and consequent depression, one woman found immediate relief after one of the olfactory bulbs was surgically removed.
[Picture on page 23]
[Picture on page 23]
[Picture on page 23]
Freshly mowed hay