2015 Hearing & Balance

Critical fact iconCanal orientation

HORIZONTAL CANALS

  • deflection of the stereocilia TOWARD the utricle causes depolarization

BOTTOM LINE:  depolarization occurs in the SAME direction as the head movement (LEFT head turn produces depolarization in the LEFT horizontal canal)

Horizontal canal activation

ANTERIOR AND POSTERIOR CANALS

  • anterior canals are located at ~90o to each other (41o to the sagittal plane)

  • posterior canals are also located at ~90o to each other

  • the directionality of the stereocilia is different in the anterior and posterior canals (in contrast to the horizontal canals, depolarization occurs in a direction AWAY from the utricle in both cases)
    • the anterior canals have their kinocilium anterior to the stereocilia
    • the posterior canals have their kinocilium posterior to the stereocilia

  • the natural pairing of A/P canals is:
    LEFT ANTERIOR with RIGHT POSTERIOR
    RIGHT ANTERIOR with LEFT POSTERIOR
    • in order to produce a stimulation of one A/P pair of canals in isolation, the direction of stimulation is a tilt (e.g., forward and left)
    • i.e., the preferred angle for stimulation is OPPOSITE FOR THE ANTERIOR CANAL ON ONE SIDE AND THE POSTERIOR CANAL ON THE OTHER

  • therefore, tilting your head forward (without a tilt to the left or right) causes DEPOLARIZATION of the ANTERIOR CANALS and HYPERPOLARIZATION of the POSTERIOR CANALS
BOTTOM LINE:  for anterior and posterior canals depolarization occurs in the SAME direction as the head movement (FORWARD head tilt produces depolarization of the ANTERIOR canals)

Canal orientation

* arrowheads indicate the location of the kinocilium (tallest stereocilia)

Email: Dr. Janet Fitzakerley | ©2015 University of Minnesota Medical School Duluth | Last modified: 7-feb-15 5:01 PM