Final answer:
The receptors that report the position of the head in space are in the utricle and saccule of the inner ear, and tiny stones called otoliths, embedded in a gel, roll in response to gravity to indicate head position to the brain.
Step-by-step explanation:
These receptors, which report the position of the head in space, are part of the vestibular system, specifically located in the utricle and saccule.
Tiny stones found in a gel overlying the hair cells roll in response to the pull of gravity. These tiny stones are called otoliths, and they are calcium carbonate crystals embedded in the otolithic membrane. The otolithic membrane shifts when the head is tilted due to gravity, causing the stereocilia on hair cells to bend.
This bending results in some hair cells depolarizing and others hyperpolarizing. The pattern of hair-cell depolarization is then interpreted by the brain to deduce the exact position of the head in space.