What happens to the cupula when endolymph fluid is stimulated?

The correct answer indicates that when the endolymph fluid within the semi-circular canals of the inner ear is stimulated, it causes the cupula to bend. This bending occurs due to the movement of the endolymph relative to the cupula, which is a gelatinous structure that sits atop the hair cells in the ampulla of each semi-circular canal.

As the endolymph moves, it exerts force on the cupula, leading to its displacement. This bending action is crucial because it mechanically stimulates the hair cells embedded in the cupula. When the hair cells are stimulated, they generate nerve impulses that are sent to the brain, providing critical information about the direction and speed of head movements. This process plays a vital role in maintaining balance and orientation.

The other options describe scenarios that do not accurately reflect the physiological response of the cupula to endolymph fluid movement. The cupula does not stop functioning or dissolve, nor does it remain unaffected under these conditions. Instead, its deformation due to endolymph movement is essential for the sensory transduction of motion and spatial orientation.