Maintaining our balance

Have you ever seen an acrobat walking on a rope or a mountain climber in action? Or its better to give a better example that might be more familiar to you? Remember what you do on your bicycle to keep from falling off. At the slightest mistake, the acrobat might topple from the rope, the climber might slip off the cliff face, and you might fall off your bicycle. While you are making unconscious (reflex) movements to keep your balance, have you ever thought about what busy operations are going on in the ear’s system? It has been equipped with very sensitive receptors which help you stay stable during your continual, different movements. Those receptors immediately recognize the changes occurring as a result of your slightest motion; they warn your body to adjust to your new position by sending out information to the spinal cord and to brain about the new situation.

How do you feel the sensation of balance and how do you react with the right reflex action? To find an answer to that, you need to re-examine ear’s anatomical structures mentioned before. At the base of its semi­circular canals there is a bulb-like enlargement which opens to the saccule and the utricle. Three semicircular canals are situated at 90-degree angles to each other in three-dimensional space.

Semicircular canals contain few sensory hair cells but there are plenty of them in the bulb-like enlargement. The strands of these cells, placed delicately, have enough elasticity to twist and bend during movement. The receptors for balance in saccule and utricle are covered with a thin membrane containing gelatinous layer and tiny calcite crystals (cupula terminalis). Depending on its density, the endolymph fluid in semicircular canals moves against the direction that your head and body move in. Similar to the uncontrolled movement of passengers in an accelerating or moving vehicle, depending on speed and direction, movement and speed of endolymph differs from general movement of your body. For example, when a car turns right, passengers move to the left with turning acceleration, and when a fast-moving car brakes suddenly, the passengers are thrown forward. Similarly, depending on its acceleration and momentum, every change in your movement causes fluid in semicircular canals to move. Triggered by movement of endolymph fluid, gelatinous mass with the calcite pieces is displaced, causing strands of the receptors to twist. Every movement of your head warns cells of different parts, and via the vestibular nerve (nervus vestibularis) the nervous system is notified of changes occurring in your balance.