BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: smell

Unlock the POV of Pups: How Dogs See the World Beyond Colors.

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On October 19, 2023

In Student Post

Madsen the dog, 001

Have you ever wondered how your furry friends recognize the world around them? This question was asked by a group of scientists who recently studied how canines “see” the world not only with their eyes, but also with their nose.

For a long time, the world believed that dogs could only see the world in black and white, or that dogs could only perceive color weakly, if at all. However, this myth was debunked in 1989 by ophthalmologist Jay Neitz and his colleagues, who discovered that dogs can indeed see colors, specifically blues and yellows. They cannot perceive reds and greens, similar to color-blind human.
Assorted Red and Green Apples (deuteranope view)

The reason why dogs can’t process light as well as most human is because they only have two types of color-sensing receptors, called cones, in their retinas, similar to many mammals: cats, pigs, and raccoons. This differentiates them from humans which have three cones. In addition, most dogs have 20/75 vision, meaning that they need to be 2o feet away to see as clear as a human would from 75 feet. Their world may be somewhat blurry compared to ours.

To truly understand how dogs see the world, we must look beyond their ability to process color, as highlighted by Sarah-Elizabeth Byosiere. Dogs rely on various other senses to help them “see,” or identify objects and movements around them. For example, unlike humans who have difficulty seeing in dark environments, dogs’ eyes are made to see in both daytime and nighttime. This is because of their abundance of rods, a type of photoreceptor cell in the retinas, which aids in night vision. Rods are 500-1000 times more sensitive to light than cones which allows dogs to see better in the dark. Dogs also have a unique structure in their eyes called the Tapetum Lucidum(Shown in diagram below), which acts like a mirror that reflects light back onto the retina. This enables them to see in conditions with six times less light than what human requires to see.

This is also the reason why dogs’ eyes will glow in photos in the dark, because their Tapetum Lucidum reflects the light back.

(Structure of eyes)

Mammal eye structure (tapetum lucidum)

Another significant aspect of dogs’ perception is their sense of smell, they are 10,000 to 100,000 times stronger than that of an average human. Dog’s mighty sense of smell plays a crucial role in how they perceive the world, they can even pick up odors from as far as 12 miles. Another study published recently in the Journal of Neuroscience revealed a direct connection between dogs’ olfactory bulb, which processes smell, and their occipital lobe, which processes vision. This integration of sight and smell was not observed to happen on any of other animal species.

While human are good at recognizing different colors, dogs are more into their sense of smell that humans can’t appreciate. Dogs aren’t missing out on anything; they just have their own unique way of exploring the world around them.

In AP Biology, we learned about how neurons transmit signal to the brain when we touch, hear, see, and smell. When vision and smell is received by optic nerve in eyes and olfactory sensory neurons in noses, they will pass the information of the sight and smell to the brain through neurons. Neurons transmit signals simply through a flow of ions across the axon membrane, which reverses the distribution of charges of the neuron compared to when it is at rest. This is how a neuron passes a signal to another neuron, they will repeat this process until they reach the occipital lobe and olfactory bulb in the brain where the information of the sight and smell will be processed and analyzed.

As a biology student, I have always wondered about how canines, mankind’s best friend, and how other animals see the world in their perspective. It is fascinating to find out that all animals have their unique way of sensing the world and collecting information from the area around them. Their “sensing” strategy are often different from ours’s; human primarily uses vision to receive information of the world, but our neighbors on earth could be using their sense of smell, sense of hearing, and even echoing to accomplish the same goal! Let me know in the comments below if you are also curious about how other animals recognize our world or if you are interested in this topic! Share your thoughts with me! If you want further information about this post or on this topic in general, please go to ScientificAmerican.com for more information and further research.

To Smell or Not to Smell?: The Dangers of Covid-19 on your Senses

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On December 31, 2020

In Student Post

Out of all the symptoms caused by Covid-19, one of the most bizarre was the complete loss of taste and smell. The loss of taste and smell, more formally known as anosmia and ageusia, is now a very common symptom of Covid-19. Over 80% of people who catch the virus experience it, and it has become one of the most effective ways to diagnose the virus. However, the loss of taste and smell is different for Covid-19 than a regular cold or flu. For Covid-19 loss of taste and smell occurs regardless of a stuffy nose and it can last from 8 days to a whole month. In worse case scenarios those senses don’t come back at all.  Although this is a widely known symptom of Covid-19, have you stopped and wondered why this occurs? 

At first there was a lot of confusion as to why the virus affected our taste and smell. Some scientists thought signs of anosmia meant Covid-19 had entered the brain through the nose. This then damages the olfactory sensory neurons (sensory neurons in the nose) causing lasting damage to the brain. However, with more research and data this fortunately doesn’t seem to be the case. Experts at the Harvard Medical School have been conducting research on this topic and have come up with a possible reason why people have been experiencing anosmia.  To understand how the virus affects people, you first need to know how the virus enters the body. The virus enters the body through a process called receptor-mediated endocytosis. The virus enters the body through the nose and mouth then binds to a certain receptor called the ACE2 receptor protein found in many parts of the body, such as the lungs, liver and kidney. After binding to the receptor the virus enters the cell and releases its own genetic material that gets copied to produce more of it as well as more viruses to spread to the whole body. The researchers at the Harvard Medical School have found that olfactory sensory neurons don’t contain the ACE2 receptor protein, so there isn’t a way that the virus could enter through those cells. Instead they believe the virus affects nonneuronal cells that support the olfactory sensory neurons, such as basal cells and sustentacular cells found in the olfactory epithelium. The virus affecting these cells is what might be causing the loss of smell due to the sensory neurons not being able to function properly without it’s normal support.  There is a lot less known about why the loss there is a loss of taste as well, since taste receptor cells also don’t contain the ACE2 receptor protein. There is still a lot of speculation and a lot more research needed to be done.  However this is good progress and some insight as to how this virus is affecting the senses. 

As stated before most Covid-19 cases people get their sense of taste and smell back, but what happens if your fully recovered and your senses still haven’t returned? In one severe case a teen named Kenny Mayfield caught the virus and has yet to get his senses back. In March, when little was known about the virus, Kenny had been suffering through Covid-19, but wasn’t sure due to lack of testing and knowledge available during that time. After several months when he tested positive for antibodies he was certain that was the case. Although he was no longer suffering from the virus itself, he still had to face the consequences of it, his sense of smell had not returned. Now months later he is still trying to regain his sense of smell. He practices scent retraining to get back his senses, but the process could take 6 months to a year for it to get back to normal. He is able to taste, but without his scent it has become less enjoyable to him, causing him to lose his appetite and lose weight. There have been several other cases just like this one. A man named Eian Kantor has gone 7 month without his senses and is desperately trying to get them back to no avail. Another woman named Freya Sawbridge has begun to regain her sense of taste and smell, but claims everything is warped and unpleasant. Not only with food, these loss of senses can be incredibly dangerous if you can’t smell a gas leak or a fire.  Covid-19 can have a serious effect on your sense of taste and smell and should be taken much more seriously.

The most important thing you can take from this article is awareness. Although it is known that you lose your sense of taste and smell due to Covid- 19, I picked this specific topic because I’ve been very curious about why and how this occurs. I wanted to know more information on it.  Many people shrug off the symptom of loss and taste and smell, because they feel guaranteed that they will get it back. However, like these cases described, it is not always a definite guarantee things will go back to normal. You could end up never getting your senses back or have them return very altered. That is why it is essential to stay safe and keep yourself and others protected. Don’t take the risk, because you could be the one person to experience long term damage that could change your life forever. 

 

Some People Can’t Smell Stinky Fish?!

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On October 19, 2020

In Student Post

A New York Times article has just reported a new “mutant superpower.” In Iceland, a brand new genetic trait was discovered, in which 2% of the population can’t smell the stinky odor of fish. 

A study of 11,326 Icelanders was conducted, in which each participant was given six “Sniffin’ Sticks (pens imbued with synthetic odors)” of cinnamon, peppermint, banana, licorice, lemon, and fish. The participants were then asked to identify the odors based on how strong each smell was and how good each Sniffin’ Stick smelled. Across the majority, the fish was rated the lowest in pleasantness. However, a small group of people actually enjoyed the scent, noting that it smelled like caramel or even a rose. 

This small group of participants was discovered to have a genetic mutation that enables the TAAR5 gene to form. TAAR5 (Trace Amine Associated Receptor 5) aids in making proteins that recognize trimethylamine (TMA), a chemical found in rotten and fermented fish, and some bodily fluids, including sweat and urine.  TAAR5 is also a G Protein, meaning that it binds guanine nucleotides. And, like other coding proteins, TAAR5 is a quaternary structured protein that has three subunits. Because this protein is incapable of binding guanine nucleotides, it means that there will be at least one “broken” copy of the gene that codes for the inability to smell fish. 

To simplify: TAAR5 recognizes the chemical of smell in fish (TMA), however, with the mutation that prevents the TAAR5 from forming, the smell of fish (TMA) is unrecognizable.

Interestingly, research has shown that this mutation may be a reaction to the customs of Iceland and a possible next step in the evolution of the region. In Iceland, fish takes a prominent place on most menus including dishes like “rotten shark.” These cultural and possibly smelly dishes may explain why this mutation is much more prominent in Iceland compared to Sweden, Southern Europe, and Africa (where the study was repeated). Bettina Malnic, an olfaction expert at the University of Sao Paulo in Brazil, commented on the luck of the region study took place, saying, “if they hadn’t looked at this population, they might not have found the variant [of TAAR5].”

I am VERY sensitive to smell and, at the same time, a lover of sushi, so it definitely fascinates me that there are people out there who don’t have to deal with the odor of smelly fish. This mutation is definitely one I wish I obtained. What do you think about this? Do you think you could have this mutation?!

 

Moles Can Smell In Stereo

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On February 11, 2013

In Student Post

BSC Photography
http://www.flickr.com/photos/bsc_photgraphy/6777273263/

We humans can see and hear in stereo. This is what leads to our 3D vision and allows us to find things easily because of our depth perception. Similarly our ability to hear in stereo allows us to roughly locate where a sound is coming from and how far away it is. But humans can’t smell in stereo, and it was widely believed that no mammal could naturally. That is until a study came out which indicates that the eastern mole, which is nearly blind, locates it’s food with the help of stereo smell.

 

Kenneth Catania, who led the research, said he came into it as a skeptic. “I thought the moles’ nostrils were too close together to effectively detect odor gradients.” Catania’s interest began when he found that the eastern mole could locate food just as quickly as its cousin, the star-nosed mole, which has a far superior sense of touch. In further tests he found that the eastern mole was remarkably quick at locating food placed in a radial chamber, indicating that they had a very sensitive sense of smell. In addition, Catania found that when he covered a mole’s right nostril, it veered to the left consistently, and when he covered the left nostril, it veered to the left consistently. This discovery is what indicated that the moles had stereo smell. Catania says this discovery “suggests other mammals that rely heavily on their sense of smell, like dogs and pigs might also have this ability”

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