Final answer:
Both the auditory and vestibular systems contain hair cells, which serve as sensory receptors, and ossicles, the tiny middle ear bones that transmit sound vibrations. However, ossicles have no direct function in the vestibular system.
Step-by-step explanation:
The structures found in both the auditory system and the vestibular system are hair cells and the ossicles. Hair cells are the sensory cells that are crucial for both hearing and balance. In the auditory system, they are within the cochlea and responsible for converting sound waves into electrical signals. In the vestibular system, they are found in the utricle, saccule, and semicircular canals, where they help detect head position and motion. The ossicles, composed of the malleus (hammer), incus (anvil), and stapes (stirrup), are middle ear bones that help transmit sound vibrations to the inner ear in the auditory system. These bones have no direct role in the vestibular system but are homologous to bones that support gills in fish, indicating a shared evolutionary origin.