What fluid fills the three semicircular canals of the inner ear?

The fluid that fills the three semicircular canals of the inner ear is endolymph. This specialized fluid is crucial for the function of the inner ear, particularly in the vestibular system, which is responsible for maintaining balance and spatial orientation. The semicircular canals are sensitive to changes in head position and movement. As the head moves, the endolymph within these canals shifts, leading to the stimulation of hair cells that send signals to the brain about the body's movements and orientation in space. This relationship between endolymph dynamics and the sensory cells is fundamental to the proper functioning of the vestibular system.