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Middle ear cavity and its contents Middle ear cavity (Tympanic cavity) Middle ear or tympanic cavity is an irregular, laterally compressed space within the temporal bone. It is filled with air, which is conveyed to it from the nasal part of the pharynx through the auditory tube. Parts of middle ear cavity The tympanic cavity consists of two parts: Tympanic cavity proper, opposite the tympanic membrane, Attic or epitympanic recess, above the level of the membrane – contains the upper half of the malleus and the greater part of the incus Contents of middle ear cavity Contents: Ossicles – malleus, incus, stapes Muscles – tensor tympani, stepedius Vessels and nerves – chorda tympani and tympanic plexus of ear. Functions of middle ear cavity Properties: Narrow, oblique, slit like, air containing cavity in the petrous part of temporal bone. Function: transmit the vibrations of tympanic membrane to the perilymph of internal ear. Boundaries of middle ear Roof (Tegmental wall) – By thin plate of bone i.e. tegmen tympani Floor (jugular wall) – Thin jugular fossa Anterior (carotid wall) – Thin plate of bone which separates the tympanic cavity from I.C.A. Posterior (Mastoid wall) – Aditus of mastoid antrum. Lateral (membranous wall) – Tympanic membrane Medial wall is formed by internal ear. Tympanic membrane moves medially Medial wall of tympanic cavity Has following features: Fenestrae vestibuli (oval window) – opening leading from the tympanic cavity into the vestibule of the internal ear – Covered by stapes Fenestrae cochleæ (round window) – leads into the cochlea of the internal ear. – Closed by the secondary tympanic membrane. Promontory – Rounded hollow prominence, formed by the projection outward of the first turn of the cochlea. Prominence of the facial canal. – Indicates the position of the bony canal in which the facial nerve is contained Tympanic Membrane Thin, semitransparent membrane, nearly oval in form. Separates the tympanic cavity from the bottom of the external acoustic meatus The greater part of its circumference is thickened, and forms a fibrocartilaginous ring which is fixed in the tympanic sulcus at the inner end of the meatus. Anterior and posterior malleolar folds Pars flaccida small, somewhat triangular part of the membrane situated above these folds is lax and thin The manubrium of the malleus is firmly attached to the medial surface of the membrane as far as its center. Most depressed part on the lateral surface is named the umbo. Ossicles – Malleus The malleus or hammer is a hammer-shaped bone Connected with the incus and is attached to the inner surface of the tympanic membrane It transmits the sound vibrations from the eardrum to the incus. Ossicles – Incus The incus or anvil is the anvil-shaped small bone It connects the malleus to the stapes The incus transmits sound vibrations from the malleus to the stapes. Ossicles – Stapes The stapes or stirrup is the stirrup-shaped small bone. Attached to the incus laterally and to the fenestra ovalis, the "oval window", medially. The oval window is adjacent to the vestibule of the inner ear. The stapes is the smallest and lightest bone in the human body. The stapes transmits the sound vibrations from the incus to the membrane of the inner ear inside the fenestra ovalis Stapedius The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes. The stapedius emerges from a pinpoint foramen in the apex of the pyramidal eminence (a hollow, cone-shaped prominence in the posterior wall of the tympanic cavity), and inserts into the neck of the stapes. Innervated by the nerve to stapedius, a branch of cranial nerve VII, the facial nerve. Tensor tympani Tensor tympani, the larger of the two muscles of the tympanic cavity, is contained in the bony canal above the osseous portion of the auditory tube. Its role is to dampen sounds, such as those produced from chewing. Origin and insertion – It arises from the cartilaginous portion of the auditory tube and the adjoining part of the great wing of the sphenoid – Inserted into the handle (manubrium) of the malleus, near its root. Auditory tube Is the channel through which the tympanic cavity communicates with the nasal part of the pharynx. 35 mm long (in adults). Extends from the anterior wall of the middle ear to the lateral wall of the nasopharynx. Has two parts – Osseous part – Cartilagenous part Mastoid or posterior wall Aditus to mastoid antrum – large aperture, leading backward from the epitympanic recess into the tympanic or mastoid antrum. – The antrum communicates behind and below with the mastoid air cells Pyramidal eminence Fossa incudis Arteries of middle ear Anterior tympanic branch (maxillary artery) Superior tympani (middle meningeal artery) and petrosal branch Posterior tympani (posterior auricular artery) Inferior tympanic (ascending Ph artery) Tympanic branch from artery of pterygoid canal. Coticotympanic from I.C artery Nerves of middle ear cavity – Tympanic branch of glossopharyngeal nerve (tympanic plexus) – Superior and inferior corticotympanic nerves from the sympathetic plexus around internal carotid artery. Veins and lymph nodes of middle ear cavity Pterygoid plexus of veins which drain into superior petrosal sinus. Lymph nodes – Periauricular and retro pharyngeal nodes. How does the sound travels? Hande of malleus and head of incus moves lateral. The long process of incus moves medially with stapes. The base of stapes pushed medially in the fenestra vestibuli and motion is communicated to perilymph in scala vestibuli. Otitis media Inflammation of the Middle Ear