Canal orientation
- SEMICIRCULAR CANALS WORK IN PAIRS, meaning that the CNS detects difference in output between opposing canals
- this is a key for interpreting lesions, which the CNS interprets as increased activity from the normal canal of the pair
- for example, nystagmus can result from the brain "misinterpretating" the afferent input from the vestibulo-ocular reflex
- this is a key for interpreting lesions, which the CNS interprets as increased activity from the normal canal of the pair
- understanding canal orientation is also critical for several tests that assess vestibular function
- in the caloric test, the head is tilted back 60o, to move the horizontal canals into the vertical plane
- in the Dix-Hallpike test, the head is rotated 45o, to allow the test of one pair of anterior/posterior canals
HORIZONTAL CANALS
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
|
* arrowheads indicate the location of the kinocilium (tallest stereocilia) |