Tectorial membrane

The tectorial membrane rests at the top of the organ of Corti, and the basilar membrane forms the base. Two types of hair cells are found along the basilar membrane. There are three rows of outer hair cells and one row of inner hair cells. The outer hair cells form part of the mechanical system of the cochlear partition, while the inner hair cells provide transduction from mechanical motion into neural firing patterns. There are about 30,000 nerve fibers in the human ear. The vast majority are afferent fibers that conduct the inner hair cell neural pulses towards the brain approximately 20 fibers are connected to each of the 1,500 inner hair cells. Approximately 1,800 efferent fibers conduct neural pulses from the brain to the outer hair cells [Pickles, 1988],... 

Outer hair cells have a special function within the cochlea. They are shaped cylindrically, like a can, and have stereocilia at the top of the cell (Figure 13), and a nucleus at the bottom. When the stereocilia are bent in response to a sound wave, an electromotile response occurs. This means the cell changes in length. Therefore, with every sound wave, the cell shortens and then elongates. This pushes against the tectorial membrane, selectively amplifying the vibration of the basilar membrane. This allows us to hear very quiet sounds. 

Grasp organ of Corti and the spiral ligament with fine forceps and tear apart from base to apex. Then, remove tectorial membrane. 

FIGURE 5.3 A depiction of the organ of Corti and its cellular structures. TM tectorial membrane elevated to show stereocilia, PC inner and outer pillar cells, DC Deiter s cells, RL reticular lamina, SC (IHC) one row of stereocilia for IHCs, SC (OHC) three rows of stereocilia for OHCs, HC Hensen s cells. Other abbreviations are as used in text. Synapses from SGCs are seen at the bottoms of IHCs with efferent axons to OHCs seen in the tunnel and passing between Deiters cells. 

FIGURE 63.1 Finite element calculation for the deformation of the cochlear partition due to pressure on the basilar membrane (BM). Outer hair cell (OHC) stereocilia are sheared by the motion of the pillars of Corti and reticular lamina relative to the tectorial membrane (TM). The basilar membrane is supported on the left by the bony shelf and on the right by the spiral ligament. The inner hair cells (IHC) are the primary receptors, each with about 20 afferent synapses. The inner sulcus (1C) is a fluid region in contact with the cilia of the inner hair cells. 

Gummer A.W., Hemmert W, and Zenner H.P. 1996. Resonant tectorial membrane motion in the iimer ear its crucial role in frequency tuning. Proc. Nad Acad. Sci. USA 93 8727-8732. 

Zwislocki J.J. andCefarattiL.K. 1989. Tectorial membrane 11 stilihess measurements in vivo. Hearing Res., 42 211 227. 

As the pressure waveform conducted by the perilymph moves within the scala tympani, the basilar membrane also begins to move, which in turn causes movement of the tectorial membrane across the hair cells of the organ of Corti. Of critical importance is the functionality of the basilar membrane, as this specialized structure displays differential frequency conductivity as a function... 

Both IHCs and OHCs have precise patterns of stereocilia at the end held within the rigid plate formed by supporting cells. The tectorial membrane overlies the stereocilia, but while those of OHCs contact the tectorial membrane, the stereodlia of the IHCs do not. At the end opposite the stereociha, IHCs synapse with the distal processes of SCCs. The proximal processes of SCCs are generally myelinated and form most of the auditory nerve. The nerve is laid down as these fibers collect from the apex and base in an orderly spiral manner. The nerve retains the frequency map of the BM, that is, it is tonotopically organized, a characteristic that carries through much of the auditory system. 

Thalmann, I., K. Machiki, A. Calabro, V.C. Hascall, and R. Thalmann. 1993. Uronic acid-containing glycosaminoglycans and keratan sulfate are present in the tectorial membrane of the inner ear functional implications. Arch. Biochem. Biophys. 307 391-396. 

---