macula

The maculae are specialized sensory patches found in the saccule and utricle of the vestibular system (inner ear). Each macula consists of hair cells whose stereocilia are embedded in an overlying otolithic membrane — a gel layer laden with calcium carbonate crystals called otoliths (or otoconia). Gravity and linear acceleration displace the otolithic membrane, bending the hair cell cilia and generating nerve impulses that signal head position and linear motion.

The utricular macula is oriented horizontally and detects horizontal linear acceleration (e.g., moving forward in a car) and head tilting. The saccular macula is oriented vertically and detects vertical linear acceleration (e.g., going up in an elevator). Together, the two maculae provide complementary information about head position relative to gravity and linear movement in three-dimensional space.

The striola is a curved line that divides each vestibular macula into two zones with opposing hair cell orientations. In the utricle, hair cells on either side of the striola point toward it; in the saccule, they point away from it. This opposing arrangement allows the macula to detect the direction of linear forces — depolarization occurs on one side while hyperpolarization occurs on the other, providing directional sensitivity.