Chapter 10 - Ear

Abstract

This chapter describes the specialized anatomy, physiology, pathology, and techniques that apply to investigating potential toxic insults to the ear. This system serves two functions—hearing and balance. Sound is sensed in the cochlea, specifically the organ of Corti (spiral organ), with transmission of vibrations from the tympanic membrane, through the middle ear ossicles, to the cochlea, and thence as electrical impulses through the cochlear portion of cranial nerve (CN) VIII to the brain. Balance is sensed by the “gyroscopes” of the vestibular apparatus, including the semicircular canals as well as the utricle and saccule, which have specialized structures to sense changes in fluid inertia (i.e., motion) and gravity (or linear acceleration); this information is forwarded to the brain via the vestibular portion of CN VIII. Systemic exposure to certain xenobiotic classes may induce ototoxicity by damaging the sensory hair cells, supporting cells, and/or afferent nerves in either the cochlea or the vestibular apparatus.