If you have ever spun around like a top or rolled down a hill, then you have probably experienced dizziness or vertigo. Some people even get dizzy just getting up too fast from the sofa. When you become dizzy, a part of your body that senses motion has sent the wrong signal to your brain. An amazing system in your inner ear is the key to dizziness.
The body senses whether it is upright or lying down or whether it is moving or standing still through the vestibular system, which is in the upper portion of the inner ear. See an illustration of the ear here. Here is how the system senses orientation with respect to gravity:
- It has otolithic organs that contain crystals of calcium carbonate (chalk)
- The crystals are attached to hair-like sensory nerve cells in different orientations.
- When you bend your head in different directions (forward, backward, sideways), gravity pulls on the crystals that are oriented with it.
- The crystals stimulate the hair cells to send nerve impulses to the brain.
- The brain interprets these signals to know which way the head is oriented in space.
Here is how the vestibular system senses motion:
- There are three semicircular canals for sensing motion.
- They are at right angles to one another.
- They contain fluid called endolymph and hair-like sensory nerve cells.
- As your head moves in a given direction, the endolymph lags behind because it resists a change in motion (the principle of inertia).
- The lagging endolymph stimulates hair cells to send nerve signals to the brain.
- The brain interprets them to know which way the head has moved.