The semicircular canals detect angular acceleration. The lateral (horizontal) semicircular canal ampulla contains hair cells whose kinocilia are oriented in which direction, and what is the physiological consequence of ampullopetal endolymph flow in this canal?

• A Kinocilia oriented away from utricle; ampullopetal flow inhibits the hair cells
• B Kinocilia have no directional orientation in the horizontal canal
• C Kinocilia oriented toward the utricle (utriculopetal); ampullopetal flow deflects kinocilia toward the utricle, causing excitation (increased firing) ✓
• D Ampullopetal flow always inhibits regardless of canal orientation

Explanation

In the lateral (horizontal) semicircular canal, the kinocilia of hair cells in the ampullary crista are oriented toward the utricle (utriculopetal side). Ampullopetal endolymph flow (toward the ampulla) deflects the cupula and bends stereocilia toward the kinocilium, causing depolarization and increased vestibular nerve firing. This is the basis of Ewald's first law for the lateral canal: ampullopetal flow is excitatory. In the anterior and posterior (vertical) canals, the orientation is reversed — ampullofugal flow is excitatory. This directional coding is the anatomical basis for caloric testing and the BPPV repositioning maneuvers.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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