When we touch something hot or cold

When you touch a hot object: what will you most likely do? You would probably drop it immediately or move your hand away from the source. What if it was something cold? That would probably send some chills down your spine. 

This is, again, because of your nervous system. You react so fast, that you don't even think about it happening. The nerve sends a impulse from the burning area to the burning spine. The sensory neurons enter the dorsal part of the spinal cord cell via the dorsal root of the spinal nerve. The cell bodies of these sensory neurons are located in a dorsal-root ganglion that lies just outside the spinal cord near its dorsal side. The axons of the sensory neurons then enter the spinal cord and synapse with inter neurons within the gray matter of the spinal cord. The inter neurons in turn synapse with motor neurons, the axons of which exit the cord ventrally via the ventral root, and conduct information to the muscles. In this reflex, a strong signal from the appropriate sensory cells both fires the flexor muscles and inhibits the motor neurons to the extensor muscles, and the hand is pulled back.. This crucial motor response is well under way before the signals responsible for the conscious sensation of pain (which exit the reflex pathway in the spinal cord) ever reach the brain.

Here's a tip when you touch something hot:

You know the feeling - you accidentally or unwittingly touch something which is very hot and the tip of your finger 'lights up' with an intense stinging pain. The moment you get burned, touch the tip of the offended finger to your ear-lobe. You will find that if you do this quickly enough, the stinging will go away almost instantaneously and there'll be no lasting pain or damage!

When your finger tip touches something hot, kinetic energy is transferred to your finger tip which is poorly conductive. It will, therefore, linger there for a few moments and the immediate pain you feel is that energy firing off pain receptors.

What happens when you touch your ear lobe? Well, have you ever noticed that your ear lobes always feel slightly cooler than the rest of you? That's because the fatty tissue and cartilage in there is a particularly good conductor of heat. So good in fact that if you can manage to make your reflexive response to the pain in your finger tip be to quickly touch that finger to your lobe, the laws of thermo dynamics mean that the heat will be conducted away very quickly, due to the conductivity differential between finger tip and ear lobe, stopping those pain receptors from firing, and even preventing the destruction of healthy cells by heat which would have otherwise lingered in your poorly conductive finger tip for several moments longer!

So, the next time you catch a finger in a flame, touch a hot pan on the stove, you know what to do - just whip that finger STRAIGHT to your ear lobe!

Sources: http://www.biog1105-1106.org/demos/105/unit9/media/reflexarc.pdf

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