Final answer:
The ampulla is the enlarged region at the base of each semicircular duct that contains hair cells for equilibrium transduction and communicates with the vestibule of the inner ear.
Step-by-step explanation:
The enlarged region at the base of each semicircular duct is known as the ampulla. This area is crucial for the transduction of equilibrium stimuli. Inside the ampulla are specialized structures called hair cells, whose stereocilia extend into another structure known as the cupula.
The cupula is essential for detecting head movements. When the head rotates, the fluid within the semicircular canal lags behind due to inertia, causing the cupula to deflect. This deflection bends the stereocilia of the hair cells, converting the mechanical movement into an electrochemical signal that can be processed by the brain, allowing us to perceive our body's orientation and balance. The ampulla communicates with the vestibule, which is part of the inner ear.