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Olfactory receptors are contact sites on cells in the brain and external sensors in insects that process and identify odors. They function by processing smells as a chemical reaction and converting it into a signal that can be read and understood by the brain. Smell is essential for the survival of any organism and plays a crucial role in identifying danger, suitability and health of a potential mate, and identifying poisonous substances and edible food. Smell also plays a role in taste.
An olfactory receptor is a contact site on certain cells in the brain of humans and most animals that helps process and identify odors. Many insects also have these types of receptors, although in most cases they are found on external sensors such as antennae rather than in the brain; this is because insects usually sense the smell not through a defined nose but rather through antennae that interact more directly with the environment. Regardless of their location, receptors tend to function in much the same way. They process the smell as a chemical reaction, then convert it into a signal that can be read and understood by the brain or other processing area. These receptors are how people are able to identify the smells of something in the air, and they also play a role in odor memory, i.e. memories of people, places, or experiences associated with certain smells.
Basic concept
Smell can be a rather complex thing. In most scientific circles, odors are known as “smells”. Smells are essentially chemical “signatures” that are released by most substances and creatures; they can also be created, usually as a byproduct of processes such as people sweating, flowers blooming, or things burning. Odors attach themselves to atmospheric and environmental molecules. They are interpreted in odors that organisms recognize through specific olfactory receptors.
How do they work
Receptors are generally considered to be part of the neural system in humans and most vertebrate animals. They sit on the very surface of some cell in the brain’s olfactory center and basically wait for an activation chemical to indicate a nearby smell. In insects, this system occurs in the antennae rather than in the brain, but the process is usually the same, at least chemically. Receptors tend to be specific, meaning there are different receptors for different smells.
One way to visualize this is to imagine odors as keys and receptors as individual locks. Any given odorant will bind only to its corresponding receptors, which is how odors are identified. When a receptor binds to an odorant, it is said to be “activated”. Sometimes it is possible for an odor to activate many receptors, usually if it is a complex or stratified odor.
Location specifics
In people and most animals, the olfactory receptors are clustered in small clusters at the back of the nasal cavity. There are usually millions of cells when counted individually and also a very large number of clustered bundles. Together, these groups form what is known as the “olfactory epithelium,” which acts as a kind of lining or border.
The epithelium is covered with hair-like cilia which pick up the inhaled odor molecules and send them to the receptors. The mucus that lines the nose and sinuses also helps trap these odorants, allowing them to be processed.
The importance of smell
Many biologists have argued that smell is one of the most essential tools for the survival of any given organism. In fact, nearly all living things, from simple invertebrates to humans, have at least some use for, and indeed need for, olfactory receptors. Fish, for example, have around 100 varieties of these types of sites, while humans have around 10,000. In fact, researchers believe that nearly 3% of the human genetic code goes into their construction.
Most people associate smells with immediate sensations, especially pleasure and repulsion. These sensations are important, but smell also plays a crucial unconscious and evolutionary role. It allows humans and animals to discern factors affecting everything from the suitability and health of a potential mate to identifying poisonous substances and edible food. It can also help identify danger, and some animals are said to be able to ‘smell fear’ – usually due to the ways they are able to process adrenaline and the increased sweat put off by others.
Smell interpretation process
The process from smell recognition in the olfactory center to processing and action in the brain can be very complicated. Most of the time, when the receptors first “stuck” with a smell, they permanently record the connection which is stored in the memory center of the brain. When an animal ingests a food substance that is rotten or causes disease, for example, the animal retains that smell in its memory bank. The same thing happens with good smells; this is partly why smelling something like freshly baked cookies can bring to mind childhood times spent with a grandmother or mom in the kitchen.
Smell also plays a role in taste. In most cases, the taste buds and gustatory receptors also work closely with the olfactory receptors and together these two components allow for the complete experience of any food item. People who have olfactory problems or complaints — or who have a stuffy nose from something like a bad cold — often find that foods taste different, and that’s why.
