Thursday, December 28, 2006

You Have Rocks in Your Head


Rocks in the Head are Good for Balance 10/10/2003
Next time someone says you have rocks in your head, it might be a compliment, depending on where and how big. You have rocks in your inner ears that keep you from falling over. No kidding. Fish, birds, and mammals have tiny crystals of calcite, called otoliths, that are a key ingredient in the sense of balance. This means that we all have tiny chunks of limestone in our heads.
  • How They Work: Because rocks have inertia, they resist motion when moving forward, and they fall in a gravitational field. The otoliths rest against tiny hair cells in a part of the inner ear called the utricle (in mammals, just below the semicircular canals). When you move or turn over, the hair cells sense the shearing motion of the otoliths, and report the information to the brain. This sense works in conjunction with the eyes to help you know which way is up, how fast you are moving, and which direction you are turning. A good explanation, with illustrations, can be found on the website of a clinical otolaryngologist,
  • Dr. Timothy C. Hain.
  • What They Look Like: Otoliths are microscopic. Fish have one large oblong otolith resting on a bed of hair cells in the macula (the gravity-sensing organ), whereas mammals have many smaller, irregular ones, called otoconia, surrounded by hair cells. Sometimes referred to as “ear dust,” the otoconia are too small, 30 microns or shorter, to be seen without a microscope. They are made up of calcium carbonate in a protein matrix. They form early in the embryo and are maintained throughout life. Some of the vertigo that ails seniors is due to shortage or accumulation of otoconia. Normally, debris is thought to be reabsorbed and new otoconia regenerated, but there is much still to be discovered about this sensory mechanism. In fish, the otoliths are also part of their sense of sound.
  • What’s New: Scientists just found an enzyme essential for proper otolith development. In the Oct. 10 issue of Science1, Sollner et al. found a gene they named Starmaker that when mutated, causes zebrafish to produce irregular stones with sharp edges instead of the smooth, oblong otoliths produced in normal development. This is partly because it switches the biomineralization process to produce aragonite instead of calcite, a different crystal form of calcium carbonate. (Some animals, like amphibians, actually use aragonite in their otoliths.)
    Donna Fekete, in a review of this paper in the same issue,2 has illustrations of these little rocks in the utricle and describes how they work. She says that the discovery may lead to improved medical treatments for vertigo and more: “In humans, mutations of a related protein have been linked to congenital deafness and defects in tooth mineralization,” she notes. In other words, the proteins that guide otolith development are also essential for hearing, and are involved in producing the other gemstones in our head – tooth enamel.

    1Christian Sollner et al., “Control of Crystal Size and Lattice Formation by Starmaker in Otolith Biomineralization,” Science Magazine 25 June 2003; 10.1126/science.1088443.
    2Donna M. Fekete, “Rocks That Roll Zebrafish,” Science Magazine 25 June 2003; 10.1126/science.1091171.
    Did you know this? Did you know that you have limestone in your ears? Did you know it is essential for you to stand and walk? This is amazing stuff. Consider that it is not just dust collected from a cave or wherever, but it is carefully manufactured by proteins and enzymes, that are in turn directed by the DNA code. The result are beautiful hexagonal crystals of calcium carbonate: little gems in your head. They reside in a fluid in your inner ear, enmeshed in a forest of hair cells that can sense every move they make. Then there are the lovely crystals in your teeth – that’s another amazing story, for another time.
    Everywhere they look, scientists find complex systems of interrelated parts. Slight mutations often cause complete loss of function, sometimes in several apparently unrelated systems. Without these rocks in your head, you would wobble dizzily like a drunken sailor and have a hard time just standing up. When they work, as they usually do, they work very, very well.
    The rocks are actually the simplest part of the system. The sensory apparatus that reports each movement, and the brain software that continually monitors and interprets the signals and sends the necessary messages to the appropriate muscles for rapid response, is mind boggling in sophistication. How could such things evolve without intelligent design? Get real! Whether it’s in a fish darting in the water, or an eagle dive-bombing on its prey, or a cheetah in pursuit of a gazelle, the hardware and software to accomplish such things surely overwhelms any man-made imitations, and yet we get all excited when Sony builds a robot that can walk upstairs (slowly) without falling over (sometimes). It’s time to give credit where credit is due.
    Think about these tiny gemstones the next time you watch the Olympics, and see a champion gymnast do a complex routine on the balance beam. When she nails that double-twisting dismount, stand up and cheer – not just for her, but for the Creator who thought of a good use for rocks in the head.
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