Inside the Inner Ear

The ear is much more than a hearing device, as both doctors and laymen were sharply reminded last week by the repercussions of what happened in Colonel John Glenn's inner ear when he "spun in" and banged his head on the edge of a bathtub. Just inside a man's ears is an exquisitely delicate mechanism, the workings of which are not fully understood. When that mechanism is damaged, as in Glenn's case, by what his doctors at first called "a mild concussion," medical men are sometimes baffled because they cannot see into the inner ear to find what is wrong. Most of the standard tests reveal only negative information. And doctors dare not open the ear to look.

Three Canals. Man's external ear, even at its best, is merely decorative, and the transmission of sound waves through the canal and eardrum to the tiny vibrating bones (ossicles) is a relatively simple matter of sound mechanics. When the vibrations reach the cochlea, they are converted, by a somewhat more complex process, into electrical impulses for transmission to the brain along auditory nerves.

But also contained in the innermost third of the ear, and working in far more mysterious ways, is a labyrinth of three nonhearing organs. The best known is a set of three semicircular canals. Minute changes in the flow and pressure of the fluid in these canals send the brain such signals as "You're turning to the right." Together, the canals make up what is probably the most important single "organ of equilibrium." But there are others.

In the vestibule of the inner ear are two tough capsules called the utricle (from the Latin for a little womb) and the saccule (a little bag). These contain a gelatinous material in which are suspended crystals of a chalky substance composed mainly of calcium carbonate, no bigger than grains of fine sand. In the space age, physiologists are learning much more about these otoliths (ear stones), which respond to forces of gravity or acceleration. Now otolith mechanisms are known to have an im portant function. The semicircular canals tell the brain when a man's position or posture is changing because of a turning motion. But it is the utricle that responds to acceleration, and the saccule to deceleration.

No Fracture. Glenn hit his head so hard that shock waves went rippling through his temporal bone. Since the inner and middle ears are contained in a cavity in this bone, they took the full force of the shock. The canals may have been bruised and become swollen. It is possible that the same thing happened to the utricle and saccule. There may have been some internal bleeding, though there is no direct evidence of it. It may be simply that the shock irritated the microscopic nerve endings that pick up signals from the nonhearing organs for transmission to the brain. What is clear is that Glenn's hearing is unimpaired, but when he moves his head, his brain receives garbled signals from his damaged organs of equilibrium. X rays do not show any bone fracture, and the electroencephalograph shows no brain damage.

The platoon of medical experts who have examined Glenn are unanimous in holding that his loss of balance and equilibrium has nothing to do with his having been subjected to eight or nine times the force of gravity in his space flight. Most victims of injuries to the inner ear recover in three to six weeks after no more treatment than rest and good care. Glenn's recovery is taking longer than average.

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