Author Archives: fyusuf

Come again? Researchers figure out how our ears tune out of conversations

 Have you ever had a conversation that was so boring that you found yourself tuning out? Did you instead find yourself focusing on some other noise be it a conversation nearby or the chirping of a bird?

The human ear has the incredible ability to focus on sounds of specific frequencies while simultaneously filtering out background noise. This is why we can sustain conversations in loud atmospheres. How the human ear carries out this incredible feat has been unknown until recently.

File:Anatomy of the Human Ear.svg

Ear: Source Wikimedia Commons – the Ear

On March 18, 2014, a research team led by MIT graduate student Jonathan Sellon published a paper that uncovered this mystery. They found that the size of the tiny nanopores in the tectorial membrane (a small, viscous inner-ear structure) played a key role in sound filtration. The researchers studied genetically mutated mice that had different sized pores in their tectorial membranes.

Before we go on to discuss the findings of this study lets take a brief look at how sound travels in the ear and the function of the tectorial membrane. When sound waves travel in the air they compress air molecules into compressions. When these compressions enter the ear canal and encounter the ear drum they cause it to vibrate. These vibrations in turn cause the 3 small bones of the middle-ear (the malleus, the incus and the stapes) to jiggle and push upon the cochlea, a fluid-filled spiral structure that looks like a snail shell.

 File:Organ of corti.svg

Tectorial Membrane: Source Wikimedia Commons – the tectorial membrane

Lining the inside of the cochlea are small hair cells that are covered by the tectorial membrane. The tectorial membrane has small pores known as nanopores (on average 40nm in diameter in mice). When the vibrations reach the cochlea, the tectorial membrane within slides back and forth over the layer of hair cells. This induces electrical signals to be sent to a special part of the brain that processes sound. You can think of the tectorial membrane as a carpet sliding across a wooden floor and the friction that arises as the electrical signals triggered.

So, what did the researchers find?

The researchers had 2 main findings. Firstly, they found that mice with smaller pores in their tectorial membranes could focus on sounds over smaller frequency ranges while those with larger pores could not focus on sounds as well. Secondly, they found that mice with larger pores could hear sounds over a greater range of frequencies (they have a greater overall sound sensitivity) as compared to mice with smaller pores. Therefore, optimal hearing is achieved by intermediate sized pores.

What makes this study particularly exciting is that Scientists have yet to make hearing aids that can select frequencies like the natural ear does. With these new findings better hearing aids can be produced.

So, the next time someone catches you not listening to them you can always blame your tectoid membrane!

Fardowsa Yusuf

Jonathan B. Sellon, Roozbeh Ghaffari, Shirin Farrahi, Guy P. Richardson, Dennis M. Freeman, Porosity Controls Spread of Excitation in Tectorial Membrane Traveling Waves, Biophysical Journal, Volume 106, Issue 6, 18 March 2014, Pages 1406-1413, ISSN 0006-3495, http://dx.doi.org/10.1016/j.bpj.2014.02.012.
(http://www.sciencedirect.com/science/article/pii/S0006349514001891)

http://www.dailymail.co.uk/sciencetech/article-2585686/What-dear-Researchers-discover-tiny-nanotunnels-ear-let-tune-conversations.html

http://www.wired.com/wiredscience/2014/03/ear-nanopores-hearing

H5N1 Avian Influenza: Pending Pandemic?

On January 8, 2014, an Albertan resident died after contracting H5N1 avian influenza. This was the first H5N1 related death in North America. Federal and provincial health officials were quick to reassure the public that person-to-person transmission of H5N1 influenza is “extremely rare”. In fact, of the 386 H5N1-related deaths reported to the World Health Organization (WHO) since 2003, almost all involved close contact with birds. Sure enough, later reports suggested that the Albertan resident may have contracted the virus whilst passing through an illegal bird market in Beijing.

But could H5N1 be transmitted between humans? Researchers at the Erasmus Medical Center sought to answer this question and on June 22, 2012 they published a highly controversial paper detailing how they re-engineered the H5N1 virus so that it could be transmitted between humans.

Before we discuss this exciting study, we need to take a brief look at the structure and life cycle of the Influenza virus. There are 3 subtypes of the Influenza virus: Influenza A, B and C. H5N1 is an Influenza A virus and these viruses have 2 types of proteins on their surface: Hemagglutinin and Neuraminidase. There are 18 known forms of Hemagglutinin and 11 known forms of Neuraminidase.  A  H5N1 virus has a type 5 Hemaggluttinin and a type 1 Neuraminidase on its surface.

Hemagglutinin is the protein responsible for viral cell entry. On the surface of the cells of our respiratory system are molecules called Sialic acid. Hemagglutinin on the surface of the virus binds to Sialic acid on the cell, triggering the cell to engulf the virus. Upon entry into the cell, the virus takes over and using an enzyme called a polymerase it makes many copies of itself. Eventually the cell bursts and the virus copies are released.

Influenza A virus: Courtesy of www.flickr.com

In the experiment, the researchers made H5N1 virus particles that were transmissible between ferrets (often used as an animal model for human Influenza infection). The researchers began by introducing 3 substitution mutations that had been identified in other highly transmissible Influenza viruses. A substitution mutation is a type of mutation that exchanges one base for another in the nucleotide sequence of a gene. Mutations change the structure of the associated protein. In this case, the mutated virus’s had altered Hemagglutinin on their surface.

The mutated virus’s were then manually placed in the nose of ferrets. Following infection, the researchers swabbed the noses of the infected ferrets and proceeded to infect another group of ferrets. This process was repeated multiple times. By the 10th cycle the mutant H5N1 was airborne and was being transmitted between ferrets in different cages.

The genome (genetic material) of the mutant H5N1 was analyzed and it was found that a total of 5 mutations, 4 mutations in Hemagluttinin and 1 mutation in the polymerase, was necessary for the virus to become transmissible between humans.  Researchers at Cambridge University looked for the same mutations in naturally occurring H5N1 virus’s. They found that the mutations existed individually or in pairs, but never all together in one virus.

So, is a H5N1  pandemic eminent? This is still unknown, but researchers have taken important steps in better understanding the mechanism of transmission of H5N1 Influenza virus.

For a more detailed look at the lifecycle of  Influenza viruses, check out this video.

YouTube Preview Image

Fardowsa Yusuf

References

http://arstechnica.com/science/2012/06/controversial-h5n1-bird-flu-papers-published-fuels-fears-of-airborne-mutations/

 

Has The Mystery Of Why Hot Water Freezes Faster Than Cold Water Been Solved?

The phenomenon that warmer water freezes faster than colder water has baffled scientists since ancient times. This paradoxical observation is known as the Mpemba effect, after a Tanzanian student who, much to his surprise, found that hot ice cream mixture cooled faster than cold ice cream mixture. After centuries of inadequate explanations, a team of scientists, led by Xi Zhang at the Nanyang Technological University in Singapore, claim they have uncovered this ancient mystery.

If this is your first exposure to the Mpemba effect, I can only imagine that you’re feeling more than a little skeptical. This phenomenon can seem very counterintuitive. It is important to note that the Mpemba effect is only observed under specific initial temperatures, container shapes and cooling conditions. A study carried out by Dr. Auerbach of Michigan University showed that the Mpemba effect was most likely to occur at cooling temperatures between -6°C and -12°C.

Boiling water cooling at sub zero temp. : Courtesy of  www.flickr.com
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So, what is the cause of this strange effect?

Zhang and his colleagues have found evidence which suggests that the Mpemba effect can be attributed to the unique properties of the hydrogen bonds that hold water molecules together.

They claim that when water molecules are brought close in contact with one another by hydrogen bonds, the covalent O-H bonds of water become compressed and store energy. As the water heats up, the hydrogen bonds relax and the water molecules move apart. This allows O-H bonds to relax and give up energy.

Cooling occurs when thermal energy is lost to the surroundings. The additional energy lost through the relaxation of O-H bonds causes warmer water to cool faster than colder water.

Hydrogen Bonds : Courtesy www.flickr.com

Researchers calculated the additional thermal energy lost by covalent bond relaxation and found it to exactly account for the different cooling times of the warmer and cooler water.

Although this explanation is very convincing, Zhang and his colleagues have yet to use this new theory to explain another property of water. So, while the mystery of the Mpemba effect may have been solved, more work is needed before this theory can be fully accepted.

Fardowsa Yusuf

References

  1. http://www.dailymail.co.uk/sciencetech/article-2483383/Mystery-hot-water-freezes-faster-cold-solved–strange-behaviour-atom-bonds.html
  2. http://gizmodo.com/weve-finally-figured-out-why-hot-water-freezes-faster-1455906029
  3. http://arxiv.org/abs/1310.6514
  4. http://math.ucr.edu/home/baez/physics/General/hot_water.html
  5. http://www.picotech.com/experiments/mpemba_effect/results.html