2015 Hearing & Balance

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)

ANTERIOR AND POSTERIOR CANALS

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

• posterior canals are also located at ~90^o 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

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