Which structure prevents spread of infection form middle ear to brain -
High-Yield Explanation
Ans. is 'a' i.e., Tegmen tympani o Tegmen tympani (forming the roof of middle ear cavity) separates the tympanic cavity from middle cranial fossa.o The middle ear is shaped like a cube.o When seen in the coronal section, the cavity of the middle ear is biconcave, o The boundaries of the middle ear are as follows:-I Roof or tegmental wallo Separates the middle ear from the middle cranial cavity.o It is formed by a thin plate of bone called tegmen tympani.II Floor or jugular wallo Formed by a thin plate of bone which separates the middle ear from the superior bulb of the internal jugular vein.o The floor also presents the tympanic canaliculus which transmits the tympanic branch of the glossopharyngeal nerve.III Anterior or carotid wallo The uppermost part bears the opening of the canal of the tensor tympani.o The middle part has the opening of the auditory tube.o The inferior part of the wall is formed by a thin plate of bone which forms the posterior wall of the carotid canal. This plate separates the middle ear from the internal carotid artery.IV Posterior or mastoid wallo Superiorly, is the aditus through which the epitympanic recess communicates with the mastoid antrum.o Below it is the fossa incudis which lodges the short process of the incus.o Below it is the pyramid giving attachment to the tendon of stapedius.o Vertical part of the facial canal for facial nerveV Lateral or membranous wallo Tympanic membrane alongwith the tympanic ring and sulcus.VI Medial or labrynthine wallo Promontory - rounded bulge produced by the first turn of the cochlea.o Oval window - it is posterosuperior to the promontory. It is closed by the footplate of the stapes.o Horizontal part of the facial canal - runs just above the oval window.o Round window - posteroinferior to the promontory. It is closed by the secondary tympanic membrane.o Processus cochleariformis - forms a pulley for the tendon of the tensor tympani.o Prominence of the lateral semicircular canal - above the facial canal.