Why Don’t Humans Have Whiskers? (McGill OSS)

2 minute read

Humans might not have hair as thick as chimpanzees covering their body, but our arm, leg and eyebrow hair all serves as reminders of our primate ancestry. So why don’t Homo sapiens have whiskers like other simians? To answer that, let me explain first what whiskers do, besides look adorable.

Whiskers are vibrissae, keratin filaments that grow out of different follicles than hair. Whisker follicles are much deeper than hair follicles and are surrounded by pockets of blood that amplify vibrations to better communicate information to the nerve cells beside the follicles. You may have noticed when looking at your cat that there are 2 kinds of whiskers, long and short. Long whiskers are macrovibrissae and can be moved voluntarily. Animals use these to sweep areas (called whisking) to navigate spaces and generally feel the world. Short whiskers are microvibrissae, and they cannot be moved voluntarily. These are used specifically for object recognition, whether it’s your rat’s favourite toy or your hand. 

In general, animals use whiskers to help them ‘see’ the world, navigate it and identify features. Humans used to have whiskers too (about 800 000 years ago we lost the DNA for whiskers), but have now largely integrated the function performed by whiskers into their brains, specifically into their somatosensory cortex. The human brain devotes relatively huge portions of itself to sensing and processing touch. 

Certain areas of the body, like fingertips, lips and genitals have much greater sensitivity to touch than other areas like the back or legs. A visual representation of this sensitivity to touch can be seen in the Cortical homunculus, or by performing a simple test: Have a friend use 2 pencils to touch your arm, while you close your eyes. Have them move the pencils closer and closer together. At a certain point, you will not be able to distinguish whether you are being touched by 1 or 2 pencils. Have the friend repeat this activity on your fingers, then your back. You’ll quickly notice that you have a much more sensitive sense of touch on your hands, feet and face. This test is called the 2 point discrimination test, and it’s often used to test patients for paralysis. 

So we as humans may not have cute whiskers anymore (though our simian cousins still have microvibrissae), but rest assured we’re no worse off for this loss, just slightly more dependent on our brains. 

Original article posted here: https://www.mcgill.ca/oss/article/did-you-know-history/whiskers-humans

Paper Cuts Hurt so Much Because Our Fingers Are Really Sensitive

1 minute read
Originally posted here: https://mcgill.ca/oss/article/did-you-know/paper-cuts-hurt-so-much-because-our-fingers-are-really-sensitive

You’re reading the morning paper,or turning the page on your recipe, when suddenly you notice a little line of blood, and feel a disproportionate amount of pain.

Paper cuts are tiny, barely cuts at all, more like deep scratches. So why do they hurt somuch?

Some areas of our bodies have more nerve cells than others, meaning that those areas are more sensitive to touch. A visual representation of this is seen in the cortical homunculus, a humanoid figure whose most sensitive body parts are the largest.

https://lh5.googleusercontent.com/-j4I0ok7lP_4Z1JebopsSogmBErvKvoCbGXzJIzl-rHPE84OFn0yOWBPvcKqi3qzNhuG9_1LBGgqMTQYts0-DaCrwPwKTqPG1LUvwugikH3wcITez5mZriXERhkX4Adre96CeR-D

As you can see, his hands are huge! That’s because our hands are one of our most sensitive body parts, able to detect microscopic differences in surfaces.

With that many nervesit’s no surprise that any cuts on our fingers, even those done by paper, hurt like heck. It certainly doesn’t help that we use our hands all day long, so areprone to reopening the healing cut, or getting foreign substances into it.

Curious what parts of your body are the most sensitive? Try the two-point discrimination test!Have a friend take two pencils (dull ones!) and touch them to your back in different, far apart, places. Slowly bring those pencils closer together, and note the point at which you can only feel one pencil. Then repeat the experiment on other body parts.

Everyone is different, but the image below shows the approximate distances you begin to distinguish between the two pencils at ondifferent body parts. Generallythe lips, tongue and hands are the most sensitive, and the back and shinsthe least.

https://lh3.googleusercontent.com/-YIRG0HJwdhZxyncxXtPkCHMFENiFqqxE-7GENjxgcJK8YlCTIyfR7PwHBfKaCd3m1Rao63OTf1bXli04wl6RqLrPOOsFKDgahDPmMULfar_8z79hGAll_3NAwm6QWCVcyiEUWnS