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Royalty free photo sense of smell4/2/2023 However, the extent to which pheromones actually influence our actions remains uncertain. For example, the scent of female tears apparently dampens male sexual desire. Some research suggests so: airborne molecules of sex hormones seem to alter hormone secretion in the opposite sex. Whether pheromones work similarly in humans is controversial. ![]() In other animals, pheromones carry messages of alarm and aggression, and they play an essential role in sexual attraction and reproduction. Pheromones are airborne chemicals emitted by individuals that elicit a physiological response in other members of the same species, via the olfactory system. The sense of smell plays a vital role in finding food, discriminating it from toxic substances, and appreciating its flavor (smell is a key component of what we commonly call “taste”-see below). 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. This is why an odor may trigger nearly instantaneous feelings of fear or desire before you even become fully aware of what you’re smelling. The olfactory bulb also connects directly to the limbic system, the brain area that regulates emotion. “Odorant molecules” (smells) travel through the nose to receptors and the olfactory bulb From there, patterns are transmitted to the olfactory or piriform (meaning “pear-shaped”) cortex in the higher brain for further processing. 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. How this is possible with messages from just 400 receptor cell types remains something of a mystery-and a testament to the brain’s computing power. How many odors can the human brain discriminate? Until recently, most scientists would have said something like 10,000 however, new research suggests a far greater number-perhaps a trillion. 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. Whenever a detectable molecule, or odorant, attaches to an olfactory receptor, it generates a tiny electrical impulse. 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. The axons come together in the olfactory nerve and go directly to the brain. Like all neurons, the cell also projects a thicker fiber called an axon. ![]() Each olfactory receptor cell has filaments called cilia, with receptors designed to bind to specific molecules. ![]() One thing that makes olfaction unique among the senses is that its receptor cells are themselves neurons. In humans, there are millions of such cells altogether but only several hundred (400 is a good estimate) different types of olfactory receptors. 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. They are essential for survival, having evolved to play key roles in such basic processes as feeding, mating, and avoiding danger.Īs the two chemical senses, they work by allowing tiny bits-molecules-of the outside world into the body, and binding to them. Smell and taste are the oldest of the senses.
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