What is the organ for detecting balance?

Complex neural net: There is an entire system contributing to balance and equilibrium, starting with the sensory apparatus in the limbs (proprioception), going up the spinal cord tracts to the brain stem & cerebellum, involving the neck muscles and their neuronal cell nuclei in the brainstem, the eyes and their input to the brain stem, and the inner ear. Most of these pathways end up in the brain stem, interacting.