Your Nose
Your sense of smell is located in two small patches of specialized cells located high up in each nasal passage, just under the brain case. The olfactory mucosa each contain about 10 million sensory cells. These sensory cells conduct odour signals directly to the side of the brain above them. This arrangement reflects the early evolutionary development of the sense of smell. (The other senses conduct most signals from one side of the body to the opposite side of the brain.)
The nose specializes in detecting airborne chemicals, which we interpret as odours. It is the electron configuration of a chemical that stimulates a receptor. Chemicals with similar molecular shapes tend to elicit the same odour response. It takes about 5 molecules of a chemical to excite a single receptor, and about 40 receptors must be excited to reach the threshold of detection. When these conditions are met, a nerve impulse is sent off to your brain. As the intensity of a smell increases (there are more of the associated chemicals in the air you are breathing) the response also tends to increase, up to a maximum level. After continual exposure to an odour, the response tends to decline. When you first enter a cow barn the smell of animals tends to be quite intense. After a few minutes the smell becomes much less noticeable.
Smells inform us about our chemical environment. Smells provide clues about what materials are safe to eat, what is safe to keep near us, and what items may be poisonous or contain harmful bacteria. Combined with taste, the sense of smell enhances the pleasure of eating. In the wild, predators use smell to hunt their prey, and prey animals use smell to avoid predators.
Smell also plays an important role in mate selection. The female gypsy moth, when it is ready to mate, emits a scent that can attract a male moth from miles away. All mammals, including humans, emit similar chemicals called pheromones to indicate their sexual status. While pheromones can have a significant effect on our selection of mates, the process occurs at a subconscious level. We sometimes use perfumes and colognes in an effort to enhance the effect of pheromones. In the days before ovulation, women are about a hundred times more sensitive to musk odour than men.
Other pheromones can transmit a subconscious alarm, ‘danger is near’ that we sometimes interpret as the ‘smell of fear’.
Your sense of smell is located in two small patches of specialized cells located high up in each nasal passage, just under the brain case. The olfactory mucosa each contain about 10 million sensory cells. These sensory cells conduct odour signals directly to the side of the brain above them. This arrangement reflects the early evolutionary development of the sense of smell. (The other senses conduct most signals from one side of the body to the opposite side of the brain.)
The nose specializes in detecting airborne chemicals, which we interpret as odours. It is the electron configuration of a chemical that stimulates a receptor. Chemicals with similar molecular shapes tend to elicit the same odour response. It takes about 5 molecules of a chemical to excite a single receptor, and about 40 receptors must be excited to reach the threshold of detection. When these conditions are met, a nerve impulse is sent off to your brain. As the intensity of a smell increases (there are more of the associated chemicals in the air you are breathing) the response also tends to increase, up to a maximum level. After continual exposure to an odour, the response tends to decline. When you first enter a cow barn the smell of animals tends to be quite intense. After a few minutes the smell becomes much less noticeable.
Smells inform us about our chemical environment. Smells provide clues about what materials are safe to eat, what is safe to keep near us, and what items may be poisonous or contain harmful bacteria. Combined with taste, the sense of smell enhances the pleasure of eating. In the wild, predators use smell to hunt their prey, and prey animals use smell to avoid predators.
Smell also plays an important role in mate selection. The female gypsy moth, when it is ready to mate, emits a scent that can attract a male moth from miles away. All mammals, including humans, emit similar chemicals called pheromones to indicate their sexual status. While pheromones can have a significant effect on our selection of mates, the process occurs at a subconscious level. We sometimes use perfumes and colognes in an effort to enhance the effect of pheromones. In the days before ovulation, women are about a hundred times more sensitive to musk odour than men.
Other pheromones can transmit a subconscious alarm, ‘danger is near’ that we sometimes interpret as the ‘smell of fear’.
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| A list of primary odours |
Research has been conducted to determine if there are olfactory sensors that respond only to specific chemicals, but the results are inconclusive. However, it has been shown that combinations of a few basic odours can stimulate our interpretation of most other odours.
The olfactory sensors seem to be particularly sensitive to these odours. Combinations of these seven basic odours can simulate most other odour responses.
The olfactory sensors seem to be particularly sensitive to these odours. Combinations of these seven basic odours can simulate most other odour responses.
