Why does mint make your mouth feel cold?

Why does mint make your mouth feel cold?

We can understand why ice cream makes us cold or why chewing on ice can give our mouth a chilly zing but why mint? The answer lies in a bit of mimicry.

Nerves rely on electrical pulses to send message to and from the brain. It is definitely in our best interests to know when something is hot or cold so we have receptors all over our bodies that can send nerve signals to the brain when triggered by temperature changes. The mouth of course has many, one receptor protein that detects cold is called TRPM8 (for those of you who really want to know that stands for transient receptor potential cation channel, subfamily M, member 8).

When we place something cold in our mouth the drop in temperature triggers a change in the TRPM8 receptor, effectively switching it from a closed to an open state so that it allows certain ions (calcium and sodium) to flow through. This flow of ions generates the electric current that triggers the nerve signal sent to the brain, and we register the sensation of cold.

mints
photo credit: sweet via photopin (license)

So what has mint got to do with all of this? Well, it seems that a change in temperature is not the only thing that triggers the TRPM8 receptor. Other natural compounds such as menthol, eucalyptus and icilin can trigger it too. Menthol is a waxy compound present in most mints and mint oils, such as peppermint, and is responsible for the minty taste and smell. Methol is known to mimic the effect of a temperature drop on the TRPM8 receptor, when it bind to the receptor it causes its ion channel to open, just as a temperature change does. Although this mechanism is well recorded, the reason behind it is still unclear.

Of course we don’t have to eat mint to get the cold effect; TRPM8 receptors are found in many places in the body and particularly in our skin, rubbing menthol oil on the skin can give the same effect as ice… causing local desensitization and numbing and even reducing swelling.

Does sound travel faster in warm or cold air?

Does sound travel faster in warm or cold air?

Does sound travel faster in warm or cold air?

 

I was asked this by the principal of a school I was visiting during Science Week last year. I gave him the short answer… it travels faster through warm air.

Technically that is correct.. it does travel faster through warm air… the molecules in the warm air are more “excited” and will vibrate more easily. Sound needs vibration in order to work so the sound is carried more easily through the air with the more excited molecules than through air with more “still” molecules (cold air).

photo credit: Micah Taylor via photopin cc
photo credit: Micah Taylor via photopin cc

 

A good way to think of it is to imagine a line of dominoes. The air molecules are the dominoes.
Sound makes air molecules around the source vibrate and hit off the next molecule which vibrates and hits of the next (just like the dominoes hitting off each other) and the chain keeps going until the sound reaches your ear… and then the vibrations get carried on to your middle and inner ear until they are changed to electrical pulses that are sent to the brain!

And there was me thinking I was keeping this simple… back to the dominoes… just keep thinking of it like a string of dominoes. Actually that is not quite true…. for the domino model to really mimic the movement of sound you have to arrange the dominoes in concentric circles, not in straight lines. Sound travels outwards from the source in all directions.

So there you have it sound does travel faster in warm air BUT it may appear to travel farther in cold air.

This is how that works…

…if the air close to the ground is colder than the air above it then sound waves travelling upwards will be bent downwards. This is called Refraction.  These refracted sound waves can act to amplify the sound to someone standing far away.

Refraction of sound waves amplifies and focuses the sound so that it can be heard from farther away
Refraction of sound waves amplifies and focuses the sound so that it can be heard from farther away

“Sound” about right to you?