Final answer:
The fluid filling the scala media that contains high levels of potassium (K⁺) and low levels of sodium (Na⁺) is called the endolymph. The correct answer is option 2) Endolymph, low, high.
Step-by-step explanation:
The fluid that fills the scala media in the cochlea of the inner ear and contains high concentrations of K⁺ and low concentrations of Na⁺ is called the endolymph. Therefore, the correct answer to the question is option 2) Endolymph, low, high.
The scala media, also known as the cochlear duct, is the central cavity of the cochlea that contains the sound-transducing neurons. It rests between the scala vestibuli and the scala tympani, both of which are filled with perilymph, a different fluid with low K⁺ and high Na⁺ concentrations. The movement of the perilymph in the scala vestibuli and scala tympani, in response to sound vibrations, is crucial for stimulating the hair cells in the organ of Corti, leading to the transduction of sound waves into neural signals.