12/4/2023 0 Comments Auditory tube anatomy![]() The membrane is constructed of an inner epithelium derived from the pharyngeal pouch, a central fibrous layer also of pharyngeal origin, and an outer stratified squamous epithelium derived from the ectoderm of the outer ear. The pars tensa comprises the majority of the membrane the manubrium of the malleus is embedded in its dorsal aspect. The pars flaccida occupies the dorsal portion of the membrane and covers a small area of the middle ear chamber that, in dogs, is separated from the remainder of the epi- and mesotympanum. The membrane is divided into the smaller pars flaccida and larger ventral, pars tensa (Figure 123-2). The tympanic membrane is a thin, translucent, triple-layered structure with contributions from the external and middle ear. The tympanic and cochlear membranes separate the chamber from the external acoustic meatus laterally and the inner ear medially, respectively. Two membranes are found within the mesotympanic chamber: the tympanic membrane and the secondary cochlear (or round) membrane. (From Evans HE, de Lahunta A: Miller’s anatomy of the dog, ed 4, St Louis, 2013, Saunders/Elsevier.) ![]() Despite variations in the thickness of the bulla wall, which is thickest on its rostral and lateral aspects, the chamber’s interior profile remains regular.įigure 123-1 Diagrammatic view of the canine middle ear anatomy. It communicates with the tympanic cavity proper through an anterolateral-facing elliptical opening on its dorsal aspect and is lined with cuboidal or squamous cells. ![]() The ventral component of the tympanic cavity, termed the hypotympanum, is the largest of the chambers and is situated within the tympanic bulla, the spherical bone prominent ventrally. On the medial aspect of the middle chamber, level with the tympanic membrane, is found the bony promontory that accommodates the cochlear structure. The middle chamber is bounded laterally by the larger of two tympanic membranes, which separates it from the external ear the smaller secondary membrane (the cochlear membrane) is located posteriorly within this chamber. The middle component-the mesotympanum or true tympanic chamber-is a four-sided chamber lined with columnar or cuboidal epithelium and variable numbers of ciliated cells. It is lined with cuboidal or squamous epithelium with few cilia. 21 The dorsal component-the epitympanum or epitympanic recess-is the smallest of the three chambers and is largely occupied by the incus and part of the malleus. The combined volume of the compartments is related to body weight. The cavity has dorsal, middle, and ventral compartments (Figure 123-1) and is lined with respiratory mucosa contiguous, via the auditory tube, with that of the nasopharynx. The tympanic cavity, formed by the tympanic component of the temporal bone, is a bony shell situated caudal and medial to the zygoma and temporomandibular articulation. The tympanic plexus receives parasympathetic innervation from the glossopharyngeal nerve and sympathetic innervation from the cranial cervical ganglion via the carotid plexus. Its major components include the tympanic cavity, tympanic membranes, ossicles (malleus, incus, and stapes), muscles (tensor tympani, stapedius), auditory (eustachian or pharyngotympanic) tube, nerves (facial, chorda tympani, tympanic branch of glossopharyngeal, and lesser petrosal), and tympanic plexus. The middle ear is phylogenetically derived from the pharynx and separates the external acoustic meatus from the cochlear and vestibular structures of the inner ear.
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