Final answer:
The semicircular canals are stimulated by rapid movements such as quick head rotations. They contain hair cells that function similarly in both the auditory and vestibular systems to send signals to the brain.
Step-by-step explanation:
The vestibular structure that is stimulated by rapid movements is the semicircular canal. These fluid-filled structures are part of the inner ear and are responsible for detecting rotational movement of the head due to their unique orientation in three spatial planes. Each semicircular canal has a swelling called the ampulla, which contains a cluster of hair cells. When the head moves rapidly, the fluid inside the semicircular canals shifts and causes the cupula to bend. This bending motion stimulates the hair cells and sends signals to the brain, informing it about the head's motion. As for the connection between the auditory and vestibular systems, the hair cells are found in both systems and play a critical role in their functioning. The auditory system uses hair cells to translate sound vibrations into nerve signals, while the vestibular system uses hair cells to sense motion and maintain balance.