Quick Facts
The tectorial membrane is a delicate gelatinous mass extending from the limbus and resting on the spiral organ of the ear and connected with the hairs of the hair cells (Dorland, 2011).
Structure and/or Key Feature(s)
The tectorial membrane is an acellular gelatinous sheet that is found within the cochlear duct of the cochlea. It extends longitudinally in the cochlea, parallel to the basilar membrane. Its overall shape is uneven as the upper surface curves outwards while the lower surface is smooth and flat. It is thought to originate via secretion from the interdental cells of the spiral limbus. Its inner aspect is attached to the vestibular edge of the spiral limbus, while its outer aspect becomes thickened and is suspended in the endolymph of the cochlear duct (Standring, 2016).
The tectorial membrane is comprised of a variety of types of collagen, including fibrillar (II, V, and XI) and non-fibrillar (IX) collagen. It is also composed of three main glycoproteins (known as α-tectorin, β-tectorin, and otogelin) which are scattered among it. The total concentration of tectorins constitutes roughly half the total protein content of the tectorial membrane (Richardson, Lukashkin and Russell, 2008).
The free edge of the tectorial membrane has a dense thickening called the marginal band. Additionally, on the inferior surface, there is a thickening into which the outer hair cells are embedded known as Kimura’s membrane. There is also a longitudinal ridge adjacent to the inner hair cells called Hensen’s strip.
Anatomical Relations
The tectorial membrane is found within the cochlear duct of the cochlea. It is superior to the spiral organ (of Corti) and its bundles of inner and outer sensory hair cells, with which it is in direct contact with. It is inferior to the vestibular membrane. The inner edge is attached to the spiral limbus.
Function
The role of the tectorial membrane is yet to be fully elucidated, but it is thought that sections of the tectorial membrane are able to reinforce the traveling waves of vibration (representing a specific frequency), which results in a correct auditory representation of that sound. It plays a critical role in ensuring the outer hair cell bundles drive the hair bundles of the inner hair cells.
In addition, there is a higher calcium ion concentration in the tectorial membrane than in the endolymph surrounding it. This tectorial calcium ion concentration level is depleted in the presence of loud sounds, and these changes in calcium ion concentration between the membrane and the surrounding fluid have notable effects on the function of the sensory hair cells. Essentially, the tectorial membrane influences its local environment in order to mediate hearing sensitivity (Strimbu et al., 2019).
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Richardson, G. P., Lukashkin, A. N. & Russell, I. J. (2008) The tectorial membrane: one slice of a complex cochlear sandwich. Curr Opin Otolaryngol Head Neck Surg, 16(5), 458-64.
Strimbu, C. E., Prasad, S., Hakizimana, P. & Fridberger, A. (2019) Control of hearing sensitivity by tectorial membrane calcium. Proc Natl Acad Sci U S A, 116(12), 5756-5764.
