Ear.pdf

The University of Jordan Faculty Of Medicine The Ear Dr. Ahmed Salman Associate professor of anatomy & embryology The Ear The ear is divided into: 1) External (Outer) ear: consists of the auricle of the ear, external auditory meatus & ear drum. 2) Middle ear: a cavity in the petrous part of the t...

The University of Jordan Faculty Of Medicine The Ear Dr. Ahmed Salman Associate professor of anatomy & embryology The Ear The ear is divided into: 1) External (Outer) ear: consists of the auricle of the ear, external auditory meatus & ear drum. 2) Middle ear: a cavity in the petrous part of the temporal bone. 3) Internal (Inner) ear: consists of the cochlea, vestibule & semicircular canals. It lies between the middle ear laterally and the internal acoustic meatus medially. The External Ear The auricle (ear pinna): It consists of cartilage covered with skin except the lobule of the ear which is unsupported by cartilage. It • • • • • • has the following parts: Helix Antihelix. Concha of auricle. Tragus. Antitragus. Lobule of the ear External acoustic (auditory) meatus: • Its lateral 1/3 consist of cartilage and the medial 2/3 is bony. • It contains hair and modified sweat glands producing cerumen (earwax). The ear drum (Tympanic membrane): • It separates the external acoustic meatus from the middle ear. • At its center, a concavity is produced by the attachment on its internal surface to the handle of malleus. • This point of attachment is the umbo of tympanic membrane. • It has upper flaccid part (pars flaccida) & a lower tense part (pars tensa). Tympanic membrane The Middle Ear Cavity It a biconcave cavity with 6 walls: 1) Anterior (carotid) wall: Shows the following: - Opening for tensor tympani muscle.(Malleus) - Opening of Eustachian (pharyngotympanic) tube. - Bony plate separating the cavity from internal carotid artery in the carotid canal. 2) Posterior (mastoid) wall: Shows the following: - Opening (aditus) to mastoid antrum. - Pyramid: transmits stapedius muscle.(Stapes) - Vertical part of facial canal. - Posterior canaliculus for chorda tympani Mastoid wall The Middle Ear Cavity 3) Lateral (membranous) wall:  Its upper part is bony.  Its lower part is the ear drum. 4) Medial (labyrinthine) wall: Shows :  Promontory: the basal turn of cochlea.  Oval window: Above & behind promontory . (Closed by stapes)  Round window: below & behind promontory. (Closed by secondary tympanic membrane )  Horizontal part of facial canal above and behind & oval window. Labyrinthine wall Promontory The Middle Ear Cavity 5) Roof (tegmental wall): tegmen tympani which separates it from the temporal lobe of brain. 6) Floor( Jugular wall): separates the cavity from the superior bulb of internal jugular vein. Jugular wall Tegmental wall Contents of middle ear: 1) Air 2) Chorda tympani: branch from facial nerve. 3) 3 bony ossicles: Malleus, incus & stapes. 4) 2 Muscles: Tensor tympani : - Its Contraction pulls handle of malleus medially, tensing tympanic membrane to reduce the force of vibrations in response to loud sound. N.S: Mandibular nerve trunk Stapedius: Its Contraction, in response to loud sound, pulls the stapes posteriorly and prevents excessive oscillation. N.S : Facial nerve Eustachian (Pharyngotympanic tube): connects the middle ear with the nasopharynx . It allows air to enter the middle ear cavity to equalize pressure on both sides of the ear drum. It consists of: • Bony part the lateral one-third. • Cartilaginous part the remaining two-thirds. Mastoid area: • The mastoid antrum is a small cavity continuous with mastoid air cells. • It lies deep to suprameatal triangle. • The mastoid antrum is separated from the middle cranial fossa above by only the thin tegmen tympani. • The mucous membrane lining the mastoid air cells is continuous with the mucous membrane throughout the middle ear. • Therefore, infections in the middle ear can easily spread into the mastoid area & to the middle cranial fossa. The Internal Ear consists of: - Bony labyrinth: consists of the cochlea , vestibule & three semicircular canals (anterior, posterior & lateral). - Membranous labyrinth: membranous ducts and sacs within the cavities of the bony labyrinth. - All these structures lie in the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially Vestibule Cochlea Semicircular canals vestibule Cochlea