Basilar membrane
Cross section of the cochlea.
Latin	lamina basilaris ductus cochlearis
Gray's	subject #232 1056
MeSH	Basilar+membrane
Dorlands/Elsevier	l_02/12475936

The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani (see figure). Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. the Peripheral organs of the Special senses the organs of Taste ( Peripheral gustatory or Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books Elsevier, the world's largest Publisher of Medical and Scientific literature, forms part of the Reed Elsevier group The cochlea is the auditory portion of the Inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along The inner Ear is the bony labyrinth, a system of passages comprising two main functional parts the organ of hearing or Cochlea The cochlear duct (or scala media) is an Endolymph filled cavity inside the Cochlea, located in between the Scala tympani and the Scala Scala tympani is one of the Perilymph -filled cavities in the Cochlear labyrinth.

Function

Sinusoidal drive through the oval window (top) causes a traveling wave of fluid flow (snapshot of fluid streamlines as shown) in the cochlear ducts, with corresponding displacement and velocity waves on the basilar membrane. The wavelength is long compared to the duct height near the base, in what is called the long-wave region, and very short near the place where the displacement and velocity are maximized, just before cutoff, in the short-wave region.

Endolymph/perilymph separation

The fluids in these two tubes, the endolymph and the perilymph are very different chemically, biochemically, and electrically. Endolymph is the fluid contained in the Membranous labyrinth of the Inner ear. Perilymph is an extracellular fluid located within the Cochlea (part of the Ear) in 2 of its 3 compartments the Scala tympani and Scala vestibuli Therefore they are kept strictly separated. This separation is the main function of Reissner's membrane (between scala vestibuli and scala media), and is one of the functions of the basilar membrane in the hearing organ of all land vertebrates. Reissner's membrane ( vestibular membrane, vestibular wall) is a membrane inside the Cochlea of the Inner ear. Scala vestibuli is a Perilymph filled cavity inside the Cochlea of the Inner ear. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes

A base for the sensory cells

The basilar membrane is also the base for the sensory cells of hearing, the hair cells (see figure). Hair cells are the Sensory receptors of both the Auditory system and the Vestibular system in all Vertebrates. This function gave the basilar membrane its name, and it is again present in all land vertebrates. Due to its location, the basilar membrane places the hair cells in a position where they are adjacent to both the endolymph and the perilymph, which is a precondition of hair cell function.

Frequency dispersion

A third, evolutionarily younger, function of the basilar membrane is strongly developed in the cochlea of most mammalian species and weakly developed in some bird species. It is the function of frequency dispersion of incoming sound waves. In brief, the membrane is tapered and it is stiffer at one end than at the other. The dispersion of fluid waves causes sound input of a certain frequency to vibrate some locations of the membrane more than other locations. As shown in experiments by Nobel Prize laureate Georg von Békésy, high frequencies lead to maximum vibrations at the basal end of the cochlear coil (narrow, stiff membrane), and low frequencies lead to maximum vibrations at the apical end of the cochlear coil (wide, more compliant membrane). Georg von Békésy (Békésy György ( June 3, 1899 &ndash June 13, 1972) was a Hungarian biophysicist born in Budapest This "place-frequency map" can be described quantitatively by the Greenwood Function and its variants. The Greenwood function correlates the position of the hair cells in the inner ear to the frequencies that stimulate their corresponding auditory neurons

Anatomy

The basilar membrane is a pseudo-resonant structure^[1] that, like strings on an instrument, varies in width and stiffness. The "string" of the basilar membrane is not a set of parallel strings, as in a guitar, but a long structure that has different properties (width, stiffness, mass, damping, and the dimensions of the ducts that it couples to) at different points along its length. The motion of the basilar membrane is generally described as a traveling wave. ^[2] The parameters of the membrane at a given point along its length determine its characteristic frequency (CF), the frequency at which it is most sensitive to sound vibrations. The Basilar membrane is widest (0. 42–0. 65 mm) and least taut at the apex of the cochlea, and narrowest (0. 08–0. 16 mm) and most taut at the base. ^[3] High-frequency sounds localize near the base of the cochlea (near the round and oval windows), while low-frequency sounds localize near the apex.

Additional images

Diagrammatic longitudinal section of the cochlea.	Floor of cochlear duct.	Spiral limbus and basilar membrane.	Section through the spiral organ of Corti (magnified)
The reticular lamina and subjacent structures.

References

• Fritzsch B: The water-to-land transition: Evolution of the tetrapod basilar papilla; middle ear, and auditory nuclei. In: Douglas B. Webster, Richard R. Fay, Arthur N. Popper, editors (1992). The Evolutionary biology of hearing. Berlin: Springer-Verlag, 351-375. ISBN 0-387-97588-8.  

• Nageris B, Adams JC, Merchant SN (1996). "A human temporal bone study of changes in the basilar membrane of the apical turn in endolymphatic hydrops". The American journal of otology 17 (2): 245-52. PMID 8723956.  

• Kössl M, Vater M (2000). "Consequences of outer hair cell damage for otoacoustic emissions and audio-vocal feedback in the mustached bat". J. Assoc. Res. Otolaryngol. 1 (4): 300-14. PMID 11547810.  

• Nilsen KE, Russell IJ (1999). "Timing of cochlear feedback: spatial and temporal representation of a tone across the basilar membrane". Nat. Neurosci. 2 (7): 642-8. doi:10.1038/10197. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 10404197.  

• Nilsen KE, Russell IJ (2000). "The spatial and temporal representation of a tone on the guinea pig basilar membrane". Proc. Natl. Acad. Sci. U. S. A. 97 (22): 11751-8. doi:10.1073/pnas.97.22.11751. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 11050205.  

External links

• Basilar+membrane at eMedicine Dictionary
• Functional anatomy of the inner ear: plenty of images, animations, and very concise functional explanations