Lec 49_ribdasil_hisear.xml

Lec 49_ribdasil_hisear.xml - Lecture 49. Histology of the...

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Lecture 49. Histology of the Ear Lecture 49. Histology of the Ear Lecture 49. Histology of the Ear A. Ribeiro-da-Silva Reference Gartner and Hiatt, Colour Textbook of Histology , 2 nd edition, Chapter 22, pp. 524-534. Introduction The ear represents the organ of hearing as well as the organ of equilibrium and balance. The external ear receives sound waves, the middle ear transforms them into mechanical vibrations of the auditory ossicles (bones), which are transmitted to the fluid-filled spaces of the internal ear . In the internal ear , specific nerve impulses are generated which are conveyed to the acoustic nerve and to the CNS. The internal ear also contains the vestibular organs that are concerned mainly with equilibrium. External Ear The auricle (or pinna): a plate of elastic cartilage. The skin covering the ear has a distinct subcutaneous layer on the posterior surface only. External auditory meatus: outer part (a continuation of the auricular cartilage) and inner part (a canal in the temporal bone). The meatus is bounded at the medial end by the eardrum or tympanic membrane . The skin in the meatus is thin and attached to the perichondrium and periosteum. The ceruminous glands are located in the skin of the meatus and are a special variety of coiled tubular apocrine sweat glands. They secrete the cerumen (ear wax).
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Lecture 49. Histology of the Ear Lecture 49. Histology of the Ear Tympanic membrane: oval and semitransparent. It is formed of two layers of collagen fibres (outer radial and inner circular) and fibroblasts that resemble those found in tendons, except for the anterior and superior part that is devoid of collagen (that part is called Shrapnell's membrane ). The external surface of the tympanic membrane is covered by a thin layer of skin and the inner surface by the mucosa of the tympanic cavity (simple squamous to cuboidal epithelium and a thin lamina propria). Figure 1 - Middle and internal ear Middle Ear (Fig. 1) Middle ear or tympanic cavity: an air-filled space in the temporal bone, communicating posteriorly with the mastoid air cells and anteriorly with the pharynx via the auditory (eustachian) tube . Contains the auditory ossicles (malleus, incus and stapes), as well as the tendons of two small muscles, the tensor tympani and the stapedius and the chorda tympani nerve. The above muscles aid in the movements of the ossicles and tympanic membrane. Epithelium of the tympanic cavity: simple squamous, except for the region around the tympanic membrane and near the opening of the auditory tube (where it is cuboidal or columnar ciliated). Regarding the ossicles, the manubrium of the malleus is inserted in the tympanic membrane. The footplate of the stapes fits in the oval window (a hiatus in the bony labyrinth) and is held in position by fibrous ligament. The three bones are connected to one another by typical joints and are supported in the tympanic cavity by minute connective tissue ligaments. A simple squamous epithelium also covers the ossicles.
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Lecture 49. Histology of the Ear
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Lec 49_ribdasil_hisear.xml - Lecture 49. Histology of the...

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