Umami is our fifth taste. Molecules from the food and beverages we consume dissolve in our saliva and interact with taste receptors on our tongue and in our mouth and throat. Taste buds are formed by groupings of taste receptor cells with hair-like extensions that protrude into the central pore of the taste bud Figure 1. Taste molecules bind to receptors on this extension and cause chemical changes within the sensory cell that result in neural impulses being transmitted to the brain via different nerves, depending on where the receptor is located.
Figure 1. Olfactory receptor cells are located in a mucous membrane at the top of the nose. Small hair-like extensions from these receptors serve as the sites for odor molecules dissolved in the mucus to interact with chemical receptors located on these extensions Figure 2.
Once an odor molecule has bound a given receptor, chemical changes within the cell result in signals being sent to the olfactory bulb : a bulb-like structure at the tip of the frontal lobe where the olfactory nerves begin. Figure 2. Olfactory receptors are the hair-like parts that extend from the olfactory bulb into the mucous membrane of the nasal cavity. These structures are proteins that weave back and forth across the membranes of olfactory cells seven times, forming structures outside the cell that sense odorant molecules and structures inside the cell that activate the neural message ultimately conveyed to the brain by olfactory neurons.
The structures that sense odorants can be thought of as tiny binding pockets with sites that respond to active parts of molecules e. There are about functional olfactory genes in humans; each gene expresses a particular kind of olfactory receptor.
The molecules that activate the sense of smell the technical name is olfaction are airborne; they enter the body via the nose and mouth and attach to receptor cells that line the mucus membranes far back in the nose. In humans, there are millions of such cells altogether but only several hundred is a good estimate different types of olfactory receptors. One thing that makes olfaction unique among the senses is that its receptor cells are themselves neurons.
Each olfactory receptor cell has filaments called cilia, with receptors designed to bind to specific molecules. Like all neurons, the cell also projects a thicker fiber called an axon. The axons come together in the olfactory nerve and go directly to the brain. In other words, the olfactory nerve consists of neurons with one end in direct contact with the external world and the other in direct contact with the brain.
Whenever a detectable molecule, or odorant, attaches to an olfactory receptor, it generates a tiny electrical impulse. As these currents enter the complex network of the brain, it can quickly sometimes within just two or three synapses, in a tenth of a second recognize the odor.
How many odors can the human brain discriminate? Until recently, most scientists would have said something like 10,; however, new research suggests a far greater number—perhaps a trillion. The computation begins as signals are received and sorted out in the olfactory bulb, a structure on the underside of the front of the brain.
The olfactory bulb also connects directly to the limbic system, the brain area that regulates emotion. A network of connections with other parts of the brain give scents a matchless power to evoke detailed, emotionally charged memories and such complex mental states as nostalgia and longing.
Pheromones are airborne chemicals emitted by individuals that elicit a physiological response in other members of the same species, via the olfactory system. In other animals, pheromones carry messages of alarm and aggression, and they play an essential role in sexual attraction and reproduction.
Whether pheromones work similarly in humans is controversial. Some research suggests so: airborne molecules of sex hormones seem to alter hormone secretion in the opposite sex.
For example, the scent of female tears apparently dampens male sexual desire. However, the extent to which pheromones actually influence our actions remains uncertain. The other primary chemical sense, taste technically, the gustatory system , responds to molecules dissolved in liquid. These molecules enter the system via taste buds: pear-shaped structures in which receptor-bearing cells surround a central pore. There are millions of receptors onsome 10, taste buds. Most are found in the familiar bumps called papillae that cover the surface of the tongue, but some line the roof of the mouth and the back of the throat.
When a molecule of the appropriate taste binds to a receptor, the process changes the electrical charge in the receptor cell, triggering release of a neurotransmitter.
This should not be surprising, as neuroscience makes clear. Odors take a direct route to the limbic system, including the amygdala and the hippocampus, the regions related to emotion and memory. But, as with Proust, taste plays a role, too, said Murthy, whose lab explores the neural and algorithmic basis of odor-guided behaviors in terrestrial animals. When you are eating all the beautiful, complicated flavors … they are all smell.
For decades individuals and businesses have explored ways to harness the evocative power of smell. Think of the cologne or perfume worn by a former flame. And then there was AromaRama or Smell-O-Vision, brainchildren of the film industry of the s that infused movie theaters with appropriate odors in an attempt pull viewers deeper into a story — and the most recent update, the decade-old 4DX system, which incorporates special effects into movie theaters, such as shaking seats, wind, rain, as well as smells.
Several years ago, Harvard scientist David Edwards worked on a new technology that would allow iPhones to share scents as well as photos and texts.
Today, the aroma of a home or office is big business. Scent branding is in vogue across a range of industries, including hotels that often pump their signature scents into rooms and lobbies, noted the authors of Harvard Business Review article. Goldworm, who designed signature fragrances for celebrities for more than a decade before starting her own company, knows the science, too.
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