Final answer:
The ampulla at the base of each semicircular canal contains the hair cells responsible for detecting rotational head movements, which help inform our sense of balance.
Step-by-step explanation:
The hair cells within the semicircular canals are located in the ampulla at the base of each canal. These cells detect rotational movements through their stereocilia, which extend into the cupula, a gelatinous structure. When the head rotates, the fluid inside the canals lags behind, causing the cupula to deflect and bend the stereocilia of the hair cells. This action sends a signal to the brain, indicating the direction and speed of the head's rotation. The vestibular system, assisted by the semicircular canals and hair cells, contributes to our sense of balance by providing the brain with information about the head's movement in three-dimensional space.