Structural and physiological features of the organ of corti

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Abstract
Modern methods for structural analysis have during the last decades enriched our knowledge about the organ of Corti. Especially electron microscopy, but also phase contrast microscopy has been important in this development. During the last few years scanning electron microscopy has rapidly become the tool of choise for several of those problems encountered in a structural analysis of the normal and pathologically altered organ of Corti. In many ways, scanning electron microscopy forms a bridge between the light microscope and the ordinary electron microscope. This paper gives a survey of our present knowledge of the organ of Corti and of the acoustic nerve as seen by preparation, by light, and by electron microscopy and also by aid of the scanning electron microscopy. The two different populations of sensory cells in the organ of Corti, the outer and inner hair cells, have many similar features. Thus they are both provided with sensory hairs and have cytoplasmic organelles organized in a very similar way. Still the innervation of inner and outer hair cells is rather different. This difference is especially pronounced when looking at nerve endings of type 2, which are generally believed to be of efferent nature. But there is a difference not only between the efferent endings of inner and outer hair cells. Also different rows of outer hair cells and different coils have a different kind of innervation. The problem of how the sensory cells are innervated is discussed. A problem of great interest for the understanding of cochlear physiology is the fluid transport in the cochlea and the nutrition of the cells in the organ of Corti. A report is given on recept studies on particle transportation in the organ of Corti. A large part of these studies were made mainly by C. Angelborg in our laboratory [in press]. They give an interesting view on the great importance of the supporting structures in the organ of Corti and the routes of transportation of particles and presumably also fluids. The spiral ganglion was described in a book of Kellerhals, Engström and Ades [1968]. A short survey is given of these ganglion cells. This description includes a report on the two populations of ganglion cells and on the complex vascular arrangement in this region.