Atlant’s Column: The Mechanical Muscle

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Welcome to the section on which explores, analyzes and explains fascinating microscopical structures.

My grandfather was a mechanical engineer. He could spend hours poring over a technical problem. At some point he sat down at his drawing board and drew the solution with a sharp pencil and a ruler. However, his favourite problem he had never solved: How do you build a muscle?

Text by science writer Atlant Bieri
Photography by Martin Oeggerli

 Until this day, no engineer in the world knows the answer to this question. After all, the basic building blocks are easy to obtain. For one kilogram of muscle tissue you need 800 grams of water and 200 grams of protein. You can get hold of these two things in every kitchen. The tricky part is the assembly. Skeletal muscles look from afar like sausages that converge at the ends. If you cut them, half a dozen bundles emerge. One of them is displayed in the image. The blue-coloured “cotton” is connective tissue, in which the muscle bundles are packed. Each of them consists of hundreds of muscle fibres. They are only one tenth of a millimetre thick, but they can be up to 15 centimetres long. Their secret is this: Individual muscle cells joined together and formed a long chain. They no longer act as single cells, but as a kind of super cell – that’s muscle fibre.


Hydraulic Cylinders, Cables, …and the Super Computer

But what happens within them, if I bend the fingers or turn my head? Amazingly, the design with which nature has come up is not so far away from the machines of my grandfather. Each muscle fibre is filled with tiny tubes, the myofibrils. In the picture you can just see them. They contain something that looks like hydraulic cylinders. They are tiny, only a few molecules wide. But rather than with water or oil pressure they function in a much more mechanical way. Inside the cylinders are tiny feet. If they get excited they start walking along the cylinder wall and thus bring about the contraction.

Any engineer who comes this far is a genius. But he still has not made a muscle. What are still lacking are the cables. One nerve cell for every muscle fibre. If I now pick up a coffee cup, my brain commands a certain number of fibres to contract. In the next split second, the fibres relax again, but before the cup starts to sink, my brain fires signals to a second group of fibres, which take the workload of the first. In this way, the muscle fibres constantly take turns and I can drink coffee all day without my arm getting tired. This means that for a single uniform motion of my arm millions of nerve signals and just as many computer operations are needed. Thus, in the end the engineer does not fail because of the complex structure of the muscle but because of the even more complex super computer that controls it.

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Continue reading Atlant’s Column: The Ruminant Fly, January 2012, or go back to the archive