The part of internal ear responsible for hearing is

1. cochlea

2. semi-circular canal

3. utriculus

4. sacculus

 
(a) Cochlea is the part of internal ear responsible for hearing. It is connected with saccule and is a spirally coiled structure that resembles a snail shell in appearance.
Semicircular canal are membranous canal suspended in the perilymph of the bony canals and are the structures of equilibrium (balancing). Whereas, utriculus and sacculus are the parts of the balancing apparatus located within the vestibule of the bony labyrinth.
These have small stones and a viscous fluid to stimulate hair cells to detect motion and orientation.