2015 Hearing & Balance

Otolith organs (saccule and utricle)

  • detect gravity (linear acceleration), and are therefore static in function
    • stereocilia and otoconia (small calcium carbonate and protein particles) are embedded in the overlying gelatinous otolith membrane
    • added weight of the otoconia produces drag on the stereocilia when the head changes position
Otolith membrane
  • when the body is in anatomical position:
    • the patch of hair cells in the UTRICLE is nearly horizontal, with the stereocilia oriented vertically
    • the sensory epithelium is vertical in the SACCULE, with the stereocilia oriented horizontally
Utricle orientation
Saccule orientation
  • in contrast with the semicircular canals (where directionality is inherent in the structure), in the otolith organs, directionality is conferred solely by the orientation of the hair cell stereocilia

  • orientation of the stereocilia within the sensory epithelium is determined by the STRIOLA, a curved dividing ridge that runs through the middle of the MACULA – in the UTRICLE, the kinocilia are oriented TOWARD the striola, and in the SACCULE they are oriented AWAY from it
    à in any position, some hair cells will be depolarized and others hyperpolarized in BOTH otolith organs
Email: Dr. Janet Fitzakerley | ©2015 University of Minnesota Medical School Duluth | Last modified: 24-jan-15 5:16 PM