A shelf of bone, the osseous spiral lamina (OSL), extends from the modiolus to the basilar membrane. Branches of the cochlear nerve (CN) travel along the spiral lamina to the modiolus, where the main trunk of the nerve is formed. The components of the cochlear nerve are bipolar neurons whose cell bodies constitute the spiral ganglion (SG). These cell bodies are shown at higher magnification in the inset (upper right). The spiral lamina supports an elevation of cells, the limbus spiralis (LS). The surface of the limbus is composed of columnar cells.
Organ of Corti, ear, guinea pig, H&E 180; inset 380.
The components of the organ of Corti, beginning at the limbus spiralis (LS), are as follows: inner border cells (IBC ); inner phalangeal and hair cells (IP&HC); inner pillar cells (IPC ); (the sequence continues, repeating itself in reverse) outer pillar cells (OPC ); hair cells (HC ) and outer phalangeal cells (OP); and outer border cells or cells of Hensen (CH ). Hair cells are receptor cells; the other cells are collectively referred to as supporting cells. The hair and outer phalangeal cells can be distinguished in this figure by their location (see inset) and because their nuclei are well aligned. Because the hair cells rest on the phalangeal cells, it can be concluded that the upper three nuclei belong to outer hair cells, whereas the lower three nuclei belong to outer phalangeal cells.
The supporting cells extend from the basilar membrane (BM) to the surface of the organ of Corti (this is not evident here but can be seen in the inset), where they form a reticular membrane (RM). The free surface of the receptor cells fits into openings in the reticular membrane, and the “hairs” of these cells project toward, and make contact with, the tectorial membrane (TM ). The latter is a cuticular extension from the columnar cells of the limbus spiralis. In ideal preparations, nerve fibers can be traced from the hair cells to the cochlear nerve (CN).
In their course from the basilar membrane to the reticular membrane, groups of supporting cells are separated from other groups by spaces that form spiral tunnels. These tunnels are named the inner tunnel (IT ), the outer tunnel (OT ), and the internal spiral tunnel (IST ). Beyond the supporting cells are two additional groups of cells, the cells of Claudius (CC) and the cells of Btcher (CB).
KEY BM, basilar membrane CB, cells of Btcher CC, cells of Claudius CD, cochlear duct CH, cells of Hensen CN, cochlear nerve HC, hair cells IBC, inner border cells IPHC, inner phalangeal and hair cells IPC, inner pillar cells IST, internal spiral tunnel IT, inner tunnel LS, limbus spiralis OP, outer phalangeal cells OPC, outer pillar cells OSL, osseous spiral lamina OT, outer tunnel RM, reticular membrane SG, spiral ganglion SL, spiral ligament ST, scala tympani StV, stria vascularis SV, scala vestibuli TM, tectorial membrane VM, vestibular membrane