A Balancing Act
✦ Nature’s Gyroscope: Your ear does much more than hear. While the snail shaped cochlea of the inner ear (pictured below) is superbly adapted for picking up sound vibrations (by deflections of hair cells described in last week’s post), the rest of the inner ear is a complex labyrinth of tubes and chambers that keeps our lives in balance.
✦ Up, Side and Down: Since we live in a three dimensional world, we have three fluid-filled semicircular canals arranged at right angles to each other, along the x, y and z planes. Each semicircular canal senses a different movement of our head: up and down, side to side, and tilt. When we move our head, the fluid inside the canal moves and presses on a tear shaped bulb at one end. The bulb (ampulla) has a collection of mechanically sensitive hair cells embedded in a jelly like matrix. Deflection of the “hairs” triggers a message to the balance center of our brain that is interpreted as a deflection of the head. Because we have a pair of ears, the deflections are mirror images so that when one side is stimulated the other is simultaneously inhibited by the movement.
✦ Rolling Stones: Two other chambers sense horizontal and vertical accelerations of your body. The saccule detects changes in vertical movement (when you are in an elevator), and the utricle monitors horizontal movement (as when a car suddenly moves forward or stops). While these organs also have mechanically sensitive hair cells, what is different is a special overlaying membrane weighted down with tiny stones of calcium carbonate, around a protein core, called otoconia. A shearing effect of the membrane against the hair cells detects vertical and linear accelerations of your body. Sometimes, the otoconia fall into one of the semicircular canals (see image) sending conflicting signals to the brain, resulting in vertigo. Fortunately, a series of head maneuvers can restore the rolling stones back into place. Ménière’s Disease is a common cause of vertigo, accompanied by hearing loss and tinnitus. It is thought to be caused by disturbances in the fluid volume filling the inner ear. Future relief from vertigo may come from prosthetic devices, similar to a cochlear implant in the inner ear. See Physician Inventors Discuss First Device to Combat Vertigo
✦ Space Jellies: Did you know that NASA has been sending jelly fish out to space since the 90’s for microgravity research? Jellies born in space have trouble orienting and swimming back on Earth because their gravity sensors, crystals of calcium sulfate much like our otoconia, fail to develop properly. Read more: http://goo.gl/Jtj00N
A follow up on How Hearing Happens: http://goo.gl/lEHKjF