The human sense of smell
Our smelling function is carried out by two small odour-detecting patches – made up of about five or six million yellowish cells – high up in the nasal passages.
The human nose is in fact the main organ of taste as well as smell. The so-called taste-buds on our tongues can only distinguish four qualities – sweet, sour, bitter and salt -all other ‘tastes’ are detected by the olfactory receptors high up in our nasal passages.
Schizophrenics, depressives, migraine sufferers and very-low-weight anorexics often experience olfactory deficits or dysfunctions. One group of researchers claims that certain psychiatric disorders are so closely linked to specific olfactory deficits that smell-tests should be part of diagnostic procedures. Zinc supplements have been shown to be successful in treating some smell and taste disorders.
Why does smell seem to act as such a powerful memory trigger?
First, the olfactory nerve is located very close to the amygdala, the area of the brain that is connected to the experience of emotion as well as emotional memory. In addition, the olfactory nerve is very close to the hippocampus, which is associated with memory as you learned earlier in this article.
The actual ability to smell is highly linked to memory. Research has shown that when areas of the brain connected to memory are damaged, the ability to identify smells is actually impaired. In order to identify a scent, you must remember when you have smelled it before and then connect it to visual information that occurred at the same time. According to some research, studying information in the presence of an odor actually increases the vividness and intensity of that remembered information when you smell that odor again Source: VeryWell.com
Why Do We Have Two Nostrils?
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The post bellow “10 Incredible Facts About Your Sense of Smell” we shared from Everyday Health.
Here are 10 strange but true facts about our sense of smell:
1. People can detect at least one trillion distinct scents. Scientists thought that the human nose could only detect about 10,000 different smells, but that information was based on a study from 1927 and very outdated. This year, researchers from Rockefeller University tested people’s sense of smell by using different mixtures of odor molecules. The results, published in the journal Science, showed that the nose can smell at least one trillion distinct scents.
Amber Luong, MD, PhD, assistant professor at the University of Texas Health Science Center at Houston. “There, the odorant is detected by various receptors located on the nerve cells and the combination of activated nerves travel to the brain. The combination of activated nerves generates all the unique smells that we as humans can detect,” says Dr. Luong.
2. Scent cells are renewed every 30 to 60 days. The sense of smell is the only cranial nerve — nerves that emerge from the brain and control bodily functions including eye movement, hearing, taste, and vision — that can regenerate, says Luong.
3. You can smell fear and disgust. You can smell feelings of fear and disgust through sweat, and then you can experience the same emotions, according to a 2012 study published in the journal Psychological Science.
4. Smell is the oldest sense. Chemodetection — detecting chemicals related to smell or taste — is the most ancient sense, says Malaspina. “Even a single cell animal has ways to detect the chemical composition of the environment,” she adds.
5. Women have a better sense of smell than men. “Women always are better at odor and smell identification than men, and every study finds that,” says Malaspina. She says one of the reasons for this may be that women have a more developed orbital prefrontal region of the brain. It may have also evolved from an ability to discern the best possible mates, or to help women better bond with and understand newborns.
6. Age-related loss of smell is linked to race. African-Americans and Hispanics experience loss of smelling related to age earlier than Caucasians, according to a 2013 study published in the Journal of Gerontology: Medical Sciences. Researchers asked more than 3,000 adults aged 57 to 85 years to identify five common odors.
Although age-related loss of smell is common, this is the first study to examine racial differences.. Results showed non-Caucasian individuals consistently scored 47 percent lower than Caucasians, and were equivalent to being nine years older. Women from all races performed the smell test better than men, and were equivalent to being five years younger.
The exact cause for this difference is unknown, but researchers believe genetics and environment (such as exposure to nerve-damaging substances) could be factors.
7. Dogs have nearly 44 times more scent cells than humans. “Humans have five to six million odor-detecting cells as compared to dogs that have 220 million cells,” says Luong. ”We have evolved to rely less on our sense of smell, while most animals have retained this sense.”
Another fun fact about canines and smell: Dogs can distinguish non-identical twins but not identical twins based on odors, says Malaspina.
8. Loss of smell may signal future illnesses. “Decreased sense of smell may be an early sign of Alzheimer’s or Parkinson’s disease,” says Luong. Two studies presented at the Alzheimer’s Association International Conference 2014 found that a reduced ability to identify scents was associated with brain cell function loss and advancement to Alzheimer’s disease. A study published in the Annals of Neurology also found that a diminished sense of smell can precede the development of Parkinson’s disease.
9. Each human has their own distinct odor. Like fingerprints, every person has their own distinct odor. The distinct odor you have comes from the same genes that determine tissue type, says Malaspina.
10. Decline in smell may predict death within five years. A recent study published in the journal PLOS ONE found that a decreased ability to identify scents may predict death within five years. The study looked at more than 3,000 Americans aged 57 to 85, and found that people unable to identify scents like rose, orange, and peppermint were more than three times as likely to die in the next five years.
Still, having a diminished sense of smell isn’t necessarily something to panic about. Most of the things that interfere with olfactory senses are allergies and head injuries, and not factors that suggest an increased risk of death.
“We know that new brain cells are produced throughout life in a few different olfactory areas, and the earlier death may relate to the decline of cell regeneration that is occurring in other body regions as well,” says Malaspina.