Final answer:
The vestibular system, which includes the utricle, saccule, and semicircular canals, is responsible for providing sustained encoding of head orientation relative to gravity, helping maintain balance and proprioception.
Step-by-step explanation:
The organs that provide sustained encoding of head orientation relative to gravity are primarily located within your vestibular system. The vestibular system, part of the inner ear, includes the utricle and saccule, which measure head orientation and sense linear acceleration, utilizing the maculae. The maculae detect changes in head position due to shifting of calcium carbonate crystals when the head tilts. Furthermore, rotational movement is detected by the semicircular canals which encode the angular acceleration and deceleration of the head. When the head rotates, fluid shift inside the canals causes the cupula and hair cells to bend, relaying information about the direction and motion of the head. This system is integral to maintaining balance and coordinating proprioception, the body's sense of its own position and movement.