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Cold Sensors

Cold Sensors Photo Credit: Clipart.com.

Why can you feel cold even when you're sitting in a warm room? Scientists may have discovered the answer.


Transcript

Why chills are more than skin deep. I'm Bob Hirshon and this is Science Update.

You've heard of being chilled to the bone. But it turns out you can also be chilled from inside the bone—the spine, to be exact.

University of Florida neuroscientist Jiango Gu and his colleagues were looking for sensory molecules, called receptors, that can sense cold. And they found them not only in the nerve cells just under the skin, but also inside the spinal cord, which is insulated from chilly environments.

Gu:

And so this is interesting: why (do) we need cool or cold receptors inside the spinal cord where the temperature is constant?

He suspects that this could explain chills that are unrelated to external temperatures, like the ones you feel when you're sick or scared. Next, Gu's team plans to look for natural chemicals in the body that can trigger these cold receptors.

Gu:

This is the first big step, because there are so many substances inside your body, and to identify a single substance or a few substances that can activate these receptors is going to be a difficult task.

If they succeed, they can then find out if surges in these chemicals really do give you the chills. I'm Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

Does this sound familiar? You and a friend are sitting in the same room, wearing similar clothes, and one of you is perfectly comfortable, but the other feels chilly. And twenty minutes later, the difference might disappear. If the temperature in the room isn't making you feel cold, what is? That's the question this research sets out to answer.

Feelings like warmth and cold are triggered by electrical signals carried by sensory nerves. At the endings of these nerves are specialized cells called receptors, which are activated either by extreme temperatures or by certain chemicals. Peripheral nerve endings are located just under the skin, or in other places that can receive signals directly from the environment.

Central nerve endings, on the other hand, are located within the spinal cord. Because they're deep inside the body, they can't sense the temperature in the room, or a substance that's on your skin. Instead, they respond to chemical signals that happen inside you.

The receptors on peripheral nerve endings that can sense cold are well known to scientists. They respond to cold temperatures, whether it's the air on a winter day, an ice cube on your skin, or the water in a chilly swimming pool. Interestingly, they also respond to menthol—the active ingredient in cough drops. (That's why your mouth feels cool when you suck on them.)

What Dr. Gu has discovered is that these cold receptors are also found on the central nerve endings, deep inside the body. Since the temperature outside can't affect these receptors, and menthol isn't normally found inside the human body, why are they there? That's the question Dr. Gu wanted to answer.

The most likely possibility is that there are certain chemicals inside our body that can trigger these central cold receptors. Maybe some of these chemicals are released when we have a fever, which would explain why we get chills even though our body temperature is higher than normal. Maybe some of them are released in more ordinary circumstances. Dr. Gu notes that other scientists have identified a natural body chemical that activates heat receptors in the central nervous system. So it would make sense that other substances in our bodies can trigger the feeling of cold.

The problem is figuring out what these chemicals are. Testing every known body chemical on these cold receptors would be like looking for a needle in a haystack. To narrow down the field, Dr. Gu's team looked at chemicals that are similar to the one that activates heat receptors.

Now try and answer these questions:

  1. What is the difference between central and peripheral nerve endings?
  2. What are receptors? How do they relate to feelings of warmth or cold?
  3. What is the key finding of this study? What was known previously? What remains unanswered?
  4. Imagine that scientists found a natural body chemical, called Frigidin, that activated these cold receptors. What experiment would you design to see if Frigidin causes the sensation of feeling cold?

For Educators

Cool Menthol 1 and Cool Menthol 2, a pair of stories by the Australian Broadcasting Corporation's Dr. Karl Kruszelnicki, features more information about menthol and its effect on cold receptors.


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