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The chemistry behind why it hurts to step on a LEGO block



The American Chemical Society has released a video as part of its Reactions Series on why it hurts so much to step on a LEGO block with bare feet (TIME, March 3, 2016). There are two main reasons: (1) the composition of children’s LEGO blocks, and (2) the sensory receptors in people’s feet, specifically the soles of their feet.


The colourful LEGO blocks are made from ABS plastic, which is a terpolymer. ‘Ter’ is Latin for three. Inside the terpolymer are three chains of monomers that together make the polymer. The three chains of monomers are: (1) Acrylonitrile – which gives LEGO blocks their strength – in fact, their mega-strength, (2) 1,3-Butadiene – which gives LEGO blocks their resistance from snapping or breaking, and (3) Styrene – which gives LEGO blocks their shiny hard surface. With these three monomers combined, LEGO blocks do not give way to pressure, even from human feet.


When people step on a LEGO block with a bare foot, the force of the person’s weight is concentrated on the point of contact (mostly a pointed edge of the LEGO block).

The bottom of the foot can have up to 200,000 individual sensory receptors. If an average adult weighs 165 pounds (74 kilograms) it generates three million pascals of pressure pushing down onto the top surface of the LEGO block at the same time as the tough brick’s strength is pushing upward into the bare foot.


Physical pain is a chemical process called Nociception. ‘Noci’ is Latin meaning to hurt. Nociceptors are special sensory receptors on the body. They are the first line of defense in terms of notifying the brain about pain. In people’s skin their are two different types of nociceptors: (1) C Fibres – that slowly notify the brain of dull, lingering pain, and (2) A-Delta Fibres – that quickly notify the brain of sharp, piercing pain. When a person steps on a LEGO block, the A-Delta Fibres send electrical signals (communication) from the foot to the brain through neurotransmitters.

At the same time, the nociceptors activate the withdrawal reflex. A message is sent to the spinal chord (before the message goes to the brain) which removes the foot quickly from the LEGO block. So people move their foot from the LEGO block before the brain receives the message about the pain. When the brain receives the pain message, the reaction is to scream, yell, swear, say ouch, wrinkle the facial muscles, or express some form of pain.

And that’s the chemistry behind why it hurts to step on a LEGO block.





http://time.com/4246385/heres-why-it-hurts-so-much-to-step-on-a-lego/?xid=homepage


MARTINA NICOLLS is the author of:- The Shortness of Life: A Mongolian Lament (2015), Liberia’s Deadest Ends (2012), Bardot’s Comet (2011), Kashmir on a Knife-Edge (2010) and The Sudan Curse (2009).
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