The tectoria membrane (TM) is one of two acellular membranes in the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory o ...

of the inner ear, the other being the

basilar membrane The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The basilar membrane moves up and down ...

(BM). "Tectorial" in anatomy means forming a cover. The TM is located above the

spiral limbus The osseous spiral lamina consists of two plates of bone, and between these are the canals for the transmission of the filaments of the acoustic nerve. On the upper plate of that part of the lamina which is outside the vestibular membrane, the per ...

and the

spiral organ of Corti The organ of Corti, or spiral organ, is the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses' action potential. Transd ...

and extends along the longitudinal length of the cochlea parallel to the BM. Radially the TM is divided into three zones, the limbal, middle and marginal zones. Of these the limbal zone is the thinnest (transversally) and overlies the

auditory teeth of Huschke Auditory means of or relating to the process of hearing: * Auditory system, the neurological structures and pathways of sound perception ** Auditory bulla, part of auditory system found in mammals other than primates ** Auditory nerve, also known ...

with its inside edge attached to the spiral limbus. The marginal zone is the thickest (transversally) and is divided from the middle zone by Hensen's Stripe. It overlies the sensory

inner hair cells Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. ...

and electrically-motile

outer hair cells Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. ...

of the organ of Corti and during acoustic stimulation stimulates the inner hair cells through fluid coupling, and the outer hair cells via direct connection to their tallest stereocilia.

Structure

The TM is a gel-like structure containing 97% water. Its dry weight is composed of

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...

(50%), non-collagenous

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glyco ...

s (25%) and

proteoglycan Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to whic ...

s (25%). Three inner-ear specific glycoproteins are expressed in the TM, α-tectorin, β-tectorin and otogelin. Of these proteins α-tectorin and β-tectorin form the striated sheet matrix that regularly organises the collagen fibres. Due to the increased structural complexity of the TM relative to other acellular gels (such as the otolithic membranes), its mechanical properties are consequently significantly more complex. They have been experimentally shown to be radially and longitudinally

anisotropic Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...

and to exhibit

viscoelastic In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly ...

properties.

Function

The mechanical role of the tectorial membrane in hearing is yet to be fully understood, and traditionally was neglected or downplayed in many models of the cochlea. However, recent genetic , mechanical and mathematical studies have highlighted the importance of the TM for healthy auditory function in mammals. Mice that lack expression of individual glycoproteins exhibit hearing abnormalities, including, most notably, enhanced frequency selectivity in Tecb^−/− mice, which lack expression of β-tectorin. ''In vitro'' investigations of the mechanical properties of the TM have demonstrated the ability of isolated sections of TM to support travelling waves at acoustically relevant frequencies. This raises the possibility that the TM may be involved in the longitudinal propagation of energy in the intact cochlea. MIT research correlates the TM with the ability of the human ear to hear faint noises. The TM influences inner ear sensory cells by storing calcium ions. When calcium store is depleted by loud sounds or by the introduction of calcium chelators, the responses of the sensory cells decrease. When tectorial membrane calcium is restored, sensory cell function return

Additional images

File:Gray929.png, Floor of ductus cochlearis. File:Cochlea-crosssection.svg, Cross section of the cochlea.

Notes

External links

Diagram
at une.edu

at bioanim.com * {{Authority control Ear