The Human Ear - Cochlea
This downward deflection in turn causes the elastic basilar membrane to move If it were uniform, then the fluctuating pressure difference between the scala. The tectorial membrane (TM) of the inner ear is a ribbon-like strip of . Vibrations of the basilar membrane, driven by pressure difference, P, between the scalae. The bottom of these cells are attached to the basilar membrane, and the stereocilia are in contact with the tectorial membrane. Inside the.
Here the border between endolymph and perilymph occurs at the reticular lamina, the endolymph side of the organ of Corti.How the Body Works : The Organ of Corti
There are approximately 15, hair cells in each human ear see figure. This function as base of the sensory cells 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[ edit ] 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: In brief, the membrane is tapered and it is stiffer at one end than at the other.
Furthermore, sound waves travelling to the far, "floppier" end of the basilar membrane have to travel through a longer fluid column than sound waves travelling to the nearer, stiffer end. Each part of the basilar membrane, together with the surrounding fluid, can therefore be thought of as a "mass-spring" system with different resonant properties: Although the entire membrane vibrates in reponse to the pressure waves frequency theorythe point along the membrane where the wave peaks represents the frequency of the stimulus place theory.
Advanced Details regarding the intricate structure of the inner ear, provide a better understanding of how this structure transduces sound waves, encoding them for auditory perception.
The tectorial membrane: One slice of a complex cochlear sandwich
Within the cochlea lies the Organ of Corti. This structure is composed of the basilar membrane, the hair cell receptors, and the tectorial membrane. The tectorial membrane from tectum meaning roof lies over the hair cells; it serves as a shelf against which the cilia of hair cells brush upon movement. Sound waves cause the basilar membrane to move relative to the tectorial membrane. The cilia of the hair cells bend when contact is made to the tectorial membrane and the hair cell discharges.
Hearing and Hair Cells
The human cochlea contains approximately inner hair cells those lying on the inside of the cochlear coil and 12, outer hair cells those lying on the outside of the cochlear coil. Hair cells form synapses with bipolar neurons whose axons form the auditory nerve. In this way, the sound energy is efficiently transfered with little reflection from the air to the fluid-filled cochlea.
The cochlea is essentially a long tube that is divided down the middle by the basilar membrane. The sound energy entering via the oval window is all applied on one side of the basilar membrane.
Thus, sound entering the ear starts the basilar membrane vibrating. But the basilar membrane is not uniform along its length, and different parts of the basilar membrane move the most in response to different frequencies of sound.
The portion of the basilar membrane near the oval window is more narrow and stiff. It thus moves preferentially with high frequencies. At the other end, the basilar membrane is wider and more flexible. This end moves most in response to low frequencies. Thus, the basilar membrane is laid out like a piano keyboard, with different frequencies pitches moving different regions preferentially.
The primary sensory cells in the cochlea are the hair cells. They lie along the basilar membrane.
Thus, when the basilar membrane moves up and down, the hair cells move up and down. The hair cells have projections at their top called stereocilia.