Final answer:
The utricle and sacculus detect head orientation and linear acceleration in a straight line, such as gravity. They contain hair cells surrounded by support cells, and their movement in response to head movements stimulates hair cells to send signals to the brain about the position of the head.
Step-by-step explanation:
The utricle and saccule are part of the vestibular system in the inner ear and are responsible for detecting head orientation and linear acceleration in a straight line, such as gravity. They contain hair cells that are surrounded by support cells and extend stereocilia into a gelatinous membrane. A layer of calcium carbonate crystals, called otoliths, on top of the membrane makes it top-heavy. When the head is tilted, the otolithic membrane slides over the macula, bending the stereocilia and stimulating hair cells to send signals to the brain about the position of the head.