The utricle and saccule are the otolith organs within the vestibular apparatus responsible for detecting linear acceleration and head position relative to gravity. They contain hair cells embedded in a gelatinous layer topped with calcium carbonate crystals called otoconia, which shift with linear movements, stimulating the hair cells. This mechanical deflection converts physical motion into neural signals that inform the brain about changes in velocity in a straight line. This function is critical during activities like walking or riding in a vehicle. In contrast, semicircular canals detect angular acceleration. Accurate understanding of the utricle and saccule's role is essential during surgeries involving the temporal bone to avoid vestibular dysfunction.

Reference: Gray's Anatomy, Standring S., 42nd Edition.