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A touchy subject

By Pat, 20 September 2013 News

Hand.

We often use our hands to touch, but there are touch receptors throughout our bodies.
Image: woodleywonderworks/Wikimedia Commons/CC-BY-2.0

Our senses allow us to perceive what is around us. Without them, it would be very difficult to navigate our world.  We have many senses, and scientists have recently discovered just how sensitive one of them is – touch.

A number of our senses rely on organs in a specific part of our body. For example, sight relies on our eyes while hearing uses the ears, each in combination with parts of the nervous system and brain. The organs required for sight and hearing are found in the head. The sense of touch is a little different – almost the whole body is used, both inside and out.

Your sense of touch relies on something called the somatic sensory system. When you touch an object, receptors in your skin detect the applied pressure. These receptors send a signal, in the form of an electric impulse to cells called neurons, which make up the nervous system. The signal travels through the nervous system to the brain, which interprets it. The brain is usually able to tell which part of the body the signal comes from – this is why you don’t feel it in your foot when someone shakes your hand.

You may think of heat and pain as being associated with the sense of touch. However, these sensations are detected by different receptors, so the ability to sense heat and pain are often referred to as separate senses: thermoception and nociception respectively.

The receptors in our skin can detect a number of different properties of a surface, such as hardness, roughness and slipperiness. A team of researchers investigated how good our sense of touch is at telling the difference between rough and smooth surfaces.

Blindfolded volunteers used their index fingers to touch a series of polymer surfaces. The surfaces each had a series of parallel ridges, ranging in height from a few micrometres (millionths of a metre) down to a few nanometres (billionths of a metre). The researchers discovered that participants were able to detect differences in the seemingly smooth surfaces down to 13 nanometres. Such sensitivity was unexpected.

This discovery of how super-sensitive our touch really is could have applications in products that rely on this sense, such as touch-screen electronics. More research will hopefully allow greater understanding of our tactile sense.

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