ABSTRACT
The inner ear or membranous labyrinth presents several challenges when preparing it for microscopic examination and histopathological analysis. First, it contains six separate sensory organs, one for hearing (i.e., organ of Corti [OC] in the cochlea) and five for balance and equilibrium (i.e., saccular and utricular macula, superior, lateral, and posterior crista in the vestibule). These organs are surrounded by large fluid spaces that contain either perilymph that has a high sodium concentration, or endolymph that has a high potassium concentration. The membranous labyrinth and surrounding fluid spaces are embedded in the bony labyrinth of the temporal bone. It is difficult to prepare the delicate sensory epithelia for microscopic examination without causing mechanical or dissection artifacts in the tissue. Second, within each organ, there are regional variations in the density of sensory cells, their pattern of innervation, and their responses to stimulation. Third, a number of genetic mutations that affect the auditory system also involve balance and equilibrium. Thus, to fully characterize the morphological changes in the inner ear of a new mutant mouse, cells must be analyzed at representative locations throughout all of the sensory regions.
