Final answer:
The organ in the inner ear of mammals that has hair cells is the organ of Corti. It transduces sound into electrochemical signals and is essential for hearing.
Step-by-step explanation:
The organ of the inner ear of mammals that contains the hair cells is called the organ of Corti. This organ is crucial for our sense of hearing. Within the cochlea, which is a fluid-filled, snail-shaped structure, the organ of Corti is found on top of the basilar membrane. It contains mechanoreceptor hair cells that transduce movements from sound waves into electrochemical signals. These hair cells consist of both inner and outer cells, with about 3,500 inner hair cells serving as the primary auditory receptors, and approximately 12,000 outer hair cells that help fine-tune sound.
The stereocilia of these cells extend into the tectorial membrane or are embedded in it, and movements from sound waves cause these hair-like structures to bend, triggering a signal to the cochlear nerve.