Tympanic part of the temporal bone presents a narrow furrow, the "tympanic sulcus", for the attachment of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact with the retromandibular part of the parotid gland. Its lateral border is free and rough, and gives attachment to the cartilaginous part of the ear canal. Internally, the tympanic part is fused with the petrous portion, and appears in the retreating angle between it and the squama, where it lies below and lateral to the orifice of the auditory tube. Posteriorly, it blends with the
Plasma membrane H+-ATPase Plasma membrane H+-ATPase This enzyme belongs to the family of hydrolases, specifically those acting on acid anhydrides to catalyse transmembrane movement of substances. To be specific, the protein is a part of the P-type ATPase family. The systematic name of this enzyme class is ATP phosphohydrolase (-exporting). -exporting ATPase is also known as proton ATPase or more simply proton pump. Other names in common use include proton-translocating ATPase, yeast plasma membrane -ATPase, plant plasma membrane -ATPase, yeast plasma membrane ATPase, plant plasma membrane ATPase, and ATP phosphohydrolase. The yeast (Saccharomyces cerevisiae) enzyme is encoded by the gene Pma1 and hence