balance
People who have hearing loss are much more likely to have balance disorders, and vice versa. This is mainly because the primary organs for hearing and balance are in the inner ear, and they share similar biological and physiological features. This also means solutions we develop have the potential to benefit both systems. are linear. In these organs, hair bundles are embedded in a membrane that is overlayed by thousands of tiny ear stones, called otoconia. When we move our head in one direction, the otoconia, which are relatively heavy, lag behind. When we tip our heads, the otoconia are pulled down by gravity. This causes the hair bundle to bend, which triggers the vestibular branch of the eighth cranial nerve to send signals to the brain. The saccule and utricle are located at right angles to each other, so they’re more sensitive to different directions of head motion. The utricle is more responsive to head tilts and sideways motions, while the saccule strongly senses motion that is up and down or forward and backward. The three cristae sense angular accelerations (rotations) of the head. The hair cells in the cristae are located inside the organ in a sac, which is called an ampulla, that sits at the end of each curved semicircular canal. The cristae sense head rotations when the hair cells are stimulated by small movements of fluid in the semicircular canals that occur when the head accelerates in a specific plane. When the head rotates in one direction, it will stimulate transient fluid motions in the opposite direction. This fluid movement stimulates the hair bundles to bend, exciting the hair cells and the nerves as well. In this way, each of these five balance organs has different functions, sensing head motions in various directions. The brain receives information from them and compiles it all into a bigger picture. Just as both ears are important for hearing, the brain requires information from both ears to optimally understand how we are oriented in space and how we are moving.
The primary organs for hearing and balance are located in the inner ear, as shown in this detailed view (above) of the inset (top). Also, in this Creative Commons image the semicircular canals are labeled semicircular ducts, which they are also called.
a publication of hearing health foundation
winter 2022
9
