Tympanic membrane retraction over the surface and move out along the ear canal. Even if migration along the ear canal is blocked, new cells continue to grow so the surface of the eardrum becomes larger. This process of proliferation and migration can result in enlargement of a retraction pocket so that the eardrum expands and grows deeper into the ear. The majority of tympanic membrane retractions remain stable for long periods of time, or may even resolve spontaneously so that eardrum becomes normal again. Not all retractions are able to resolve even if middle ear pressure normalizes, as the retracted segment may become
Basilar membrane membrane is also the "base" for the sensory cells of hearing, the hair cells that are equipped with "Stereocilia". There are approximately 15,000 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. A third, evolutionarily younger, function of the basilar membrane is strongly developed in