Overview_of_ear - Ear Overview A. External Auditory Canal...

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Ear Overview A. External Auditory Canal 1. The structure consists of an outer half made of cartilage, and an inner half comprised of bone. Cerumen glands are found in the outer half. The canal has a downward and forward course, therefore in an adult one must pull the auricle upward and backward to straighten it. There is a more superior course in infants, therefore one must pull the auricle downward and backward. An infection of the external auditory canal is otitis externa. B. Middle Ear 1. The parts of the middle ear include the auditory ossicles and tympanic cavity and membrane. The auditory ossicles are connected by synovial joints which may undergo ankylosis resulting in otosclerosis. The middle ear is connected to the auditory (pharyngotympanic) tube, mastoid antrum and mastoid air cells. Embryologically, it is an outpouching from the pharynx, therefore it is lined with mucosa like the pharynx; and is connected to the nasopharynx by the auditory tube. The normal function of the pharyngotympanic (auditory tube) is to regulate pressure within the middle ear, and allow drainage of secretions from the middle ear. The middle ear receives its sensory innervation from cranial nerve IX (glossopharyngeal). Two muscles, stapedius (CN VII, Facial) and tensor tympani (CN V3, mandibular branch of Trigeminal) dampen sounds and protect the ear. 2. Fours Walls, Roof and Floor of the Middle ear. The middle ear can be thought of as a room with plumbing (blood vessels), electric wires (nerve), and heating/ac ducts (openings to other rooms) in its walls. a. Lateral Wall. Comprised of the tympanic membrane which is divided into two parts, the larger pars tensa, and the smaller more superior pars flaccida. The tympanic membrane faces outward, forward, and downward. The lateral process and handle (manubrium) of the malleus are attached to the tympanic membrane. The most indrawn point on the tympanic membrane is the umbo. The Chorda tympani nerve crosses the medial surface of the handle of the malleus (medial surface of the tympanic membrane). b.
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This note was uploaded on 02/17/2012 for the course MPAS PA 602 taught by Professor Dr.laird during the Fall '10 term at Chatham University.

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Overview_of_ear - Ear Overview A. External Auditory Canal...

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