Which sensory systems affect equilibrium?

• A. Visual only
• B. Vestibular only
• C. Somatosensory only
• D. Visual, Vestibular, and Somatosensory

Answer: (D)

Equilibrium depends on integrating input from vision, the vestibular apparatus, and somatosensory feedback. Vision provides a reference frame for orientation and helps anticipate movement relative to the surroundings. The vestibular system detects head motion and gravity through the semicircular canals (rotational motion) and otolith organs (linear acceleration and head position). Somatosensory information from muscles, joints, and the skin gives sense of limb position, weight bearing, and surface contact. The brain combines these signals to keep posture and stabilize gaze. If one input becomes unreliable, others can compensate to some degree, but all three contribute to balance, as seen when balancing with eyes closed relying more on vestibular and somatosensory cues, or when navigating uneven surfaces where proprioception is critical.