Tympanic membrane retraction commercially available devices (e.g. Otovent and Ear Popper). A ventilation tube, also known as a tympanostomy tube or a grommet, may be placed through the eardrum to equalize middle ear pressure. Although this intervention may be effective, research has not yet shown whether it provides better results than simple observation. Further weakness or perforation of the eardrum may occur. These are intended to improve Eustachian tube function. Adenoidectomy can improve middle ear function and nasal steroid sprays can reduce adenoid size but it is not known whether these treatments alter tympanic membrane retraction. Enlargement of the Eustachian tube opening in
Cell membrane cells to hold them together to form tissues. Fungi, bacteria, most archaea, and plants also have a cell wall, which provides a mechanical support to the cell and precludes the passage of larger molecules. The cell membrane is selectively permeable and able to regulate what enters and exits the cell, thus facilitating the transport of materials needed for survival. The movement of substances across the membrane can be either "passive", occurring without the input of cellular energy, or "active", requiring the cell to expend energy in transporting it. The membrane also maintains the cell potential. The cell membrane thus works