The Ear

The inner ear, located within the temporal bone, houses our sense of balance (vestibular sense) and hearing (auditory sense). The vestibulocochlear nerve (cranial nerve VIII) provides sensory innervation of the inner ear. The vestibular branch innervates the fluid-filled semicircular canals (balance) and the cochlear branch innervates the fluid-filled cochlea (hearing). This chapter will focus on the histology of the cochlea, which is a spiral-shaped bony cavity located within the temporal bone.

The cochlea is a spiral shaped chamber that contains a fluid-filled structure called the spiral organ (Figure 1). The spiral organ contains a ladder-like structure (scala means “ladder” in Italian) with three distinct fluid-filled chambers (scala vestibuli, scala media, and scala tympani). Found on the boundary between the scala media and scala tympani (basilar membrane) is the Organ of Corti (Figure 2). Hair cells of the Organ of Corti detect vibrational changes caused by sound waves. This sensory input is relayed through the vestibulocochlear nerve (cranial nerve VIII) to the brain.

Figure 1: The cochlea with and without illustration overlay (scanning power) 

Figure 2: The cochlea, highlighting the organ of Corti, with and without illustration overlay (high power)

IMPORTANT NOTE: The tectorial and vestibular membranes are often damaged during the slide preparation processing and may not be clearly visible.

Chapter Illustrations By:

Juan Manuel Ramiro-Diaz, Ph.D.