Which part of the inner ear primarily detects vertical linear movement?

The saccule is the correct choice for detecting vertical linear movement in the inner ear. It is one of the two otolithic organs, the other being the utricle, which are situated within the vestibule of the inner ear. The saccule is oriented vertically, allowing it to respond specifically to movements such as going up or down, as well as to gravitational forces.

Inside the saccule, hair cells are embedded in a gel-like structure that contains crystals known as otoliths. When the head moves, these otoliths shift due to inertia, bending the hair cell stereocilia and generating nerve signals that the brain interprets as vertical movement. This mechanism is crucial for balance and orientation in space.

While the utricle also detects linear acceleration, it primarily responds to horizontal movements. The cochlea, on the other hand, is responsible for hearing and does not play a role in detecting linear motion. The vestibule encompasses both the utricle and saccule but does not independently detect linear motion. Thus, the saccule is specifically adapted for detecting vertical linear movement, making it the correct answer.