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The Wonderful World of Smell: Do you know how our sense of smell begins?
The sense of smell is often underestimated in our daily lives, but its impact on emotions, memory and behavior cannot be ignored. The origin of smell is closely related to its complex physiological mechanisms. Here we will explore the basic principles of olfactory perception and related scientific research.
Olfaction receptors
Olfactory receptors (ORs) are chemical sensors present in the cell membrane of olfactory neurons that are responsible for detecting molecules with odor (i.e. odor compounds). They trigger nerve impulses that transmit odor information to the brain. In vertebrates, these receptors belong to the class A rhodopsin-responsive protein family of G protein-coupled receptors, forming the largest multigene family in vertebrates.
In humans, there are about 400 functional olfactory receptor genes, while mice have about 1,400.
Receptor structure and mechanism
Olfactory receptors are found in the cilia and synapses of neurons and are also expressed in the respiratory epithelium of humans. When odor molecules enter the nasal cavity and bind to the olfactory receptors, the receptors undergo structural changes, bind to and activate the internal G protein, and further activate adenylate cyclase to convert ATP into cyclic adenosine monophosphate (cAMP). ). These chemical reactions trigger calcium and sodium ions to enter the cell, setting up an action potential that transmits the odor signal to the brain.
Variety of smell
It is estimated that there are as many as 1,000 olfactory receptors in the mammalian genome, which accounts for about 3% of the genome. However, not all olfactory receptor genes are expressed and functional. Humans have about 400 functional genes, while the remaining 600 or so are pseudogenes. This huge number of olfactory receptors enables us to distinguish countless different smells. Each olfactory receptor does not detect just a single odor, but is sensitive to a range of structurally similar odors.
Ironically, some odor molecules can activate several different types of olfactory receptors at the same time.
The evolution and future of smell
The olfactory receptor gene family evolved in vertebrates through gene duplication and conversion. Humans have fewer olfactory genes than other mammals, which may be related to humans' high reliance on vision. However, this assumption has been called into question as studies have shown that even with a reduction in the number of genes, our ability to smell remains unchanged.
Future Research Directions
There are still many unknowns in the understanding of the construction and expression of smell. Although existing research provides us with a foundation, more efforts are still needed to determine the actual application of smell in various life situations and the reasons behind it. Biological mechanisms. The study of olfactory receptors not only has far-reaching significance for biological science, but also means how humans can better use this perception system to improve their lives.
The study of olfaction is not only about exploring the mysteries of biology, but also about understanding ourselves.
Will we see olfactory technology being used in a wide range of fields in the future, from food safety to emotional therapy?
