Part III of IV: The Inner Ear

The inner ear is a series of fluid-filled organs encased within a bony labyrinth. These organs serve two purposes - hearing and maintaining your balance.

 

Your organ of hearing is called the cochlea. The cochlea is a snail-shaped organ filled with hair cells that are organized by frequency. Hair cells that are tuned to higher pitched sounds are located at the basal end of the cochlea where sound waves are originated. Low pitches are tuned at the farthest end of the cochlea, called the apex. When fluid displaces these tuned hair cells, a signal gets sent via your cochlear nerve to your brain for your brain to interpret the sound.

 

 

Your vestibular system is a complex group of organs that work in conjunction with your vision and your proprioceptive system (knowing where your body is in space) to maintain your balance. When the fluid within these organs are displaced, they send signals to your brain informing you of movement and your orientation relative to gravity.

  • There are three semicircular canals that detect angular acceleration of the head (i.e., rolling over in bed). These canals are offset from one another so that they pick up head movements in all directions. 
  • The utricle and saccule are small organs that detect linear accelerations of the head (i.e., riding in a moving car). It is within these two organs that calcium carbonate crystals are embedded within a gelatinous membrane. 

 

A condition called benign paroxysmal positional vertigo (BPPV) occurs when the calcium carbonate crystals within the utricle and saccule get displaced into one or multiple of the semicircular canals. BPPV is characterized by brief episodes of vertigo, usually only lasting for a few seconds at a time, caused by changes in head position. This is most often experienced when lying down or rolling over in bed. BPPV is the most common form of vertigo, but luckily, it is often the easiest to treat. 

 

Other disorders of the inner ear include:

  • Meniere’s Disease - an increase in fluid pressure within the inner ear resulting in vertigo attacks, fluctuating hearing loss, tinnitus, and a perception of fullness within the ear.
  • Noise-Induced Hearing Loss - hearing loss resulting from exposure to loud sounds
  • Vestibular Neuritis - inflammation of the vestibular nerve 
  • Presbycusis - hearing loss due to aging
  • Ototoxicity - damage to hearing (and balance) from medications

 

Fun facts about the inner ear:

  • The cochlea coils around itself 2 ¾ times.
  • As we age (and with noise exposure) our ability to hear high-pitched sounds decreases first. This is because sound enters the cochlea into the higher-pitched region, wearing it out faster.
  • The cochlea is approximately the size of a pea.

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