The maculae of the utricle and saccule are the sensory organs for static equilibrium and linear acceleration. Which statement about their orientation and mechanism is correct?

• A The macula of the utricle lies in the vertical plane and responds to horizontal acceleration
• B Both maculae respond only to angular acceleration like the cristae ampullaris
• C The macula of the saccule lies in the vertical plane and signals head position relative to gravity ✓
• D Their hair cells lack a kinocilium unlike those in the ampullary crest

Explanation

The saccular macula lies in the vertical plane on the medial wall of the saccule, so it senses vertical linear acceleration and head tilt relative to gravity. The utricular macula lies horizontally on the floor of the utricle and senses horizontal linear acceleration. Both depend on otoconia (calcium carbonate crystals embedded in the otolithic membrane) whose weight bends stereocilia. Cristae ampullaris in the semicircular canals handle angular acceleration, and vestibular hair cells retain kinocilia, unlike mature cochlear hair cells.

Reference: Ganong Review of Medical Physiology, 26th ed.

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