Structure of The Ear
Overview (A, D)
The ear contains two sensory organs with different functions; morphologically they form a single complex, the inner ear, or ves-tibulocochlear organ. One part of it, the cochlea, is theorgan of hearing, or spiral organ (organ of Corti). The other part con-sists of saccule, utricle, and semicircularducts; it registers changes in body position,especially those of the head, and represents the organ of balance, or vestibular appara-tus. The ear is divided into three parts: the external ear, the middle ear, andthe internal ear.
The external ear includes the auricle (A, D1) and the external acoustic meatus (D2).
The middle ear consists of the tympanic cav-ity(D3), the mastoid cells (air cells), and the auditory tube (eustachian tube) (D4). The tympanic cavity with the auditory ossicles is a narrow space filled with air. It lies behind the eardrum and extends as the epitympanic recess (D5) above the externalacoustic meatus. The tympanic cavity merges anteriorly into the auditory tube (tympanic opening) (D6). The tube extends obliquely downward and forward and opens in front of the posterior pharyngeal wall into the pharyngeal cavity (pharyngealopening) (D7). The auditory tube is linedwith a ciliated epithelium and consists of an osseous and a cartilaginous section that join at the isthmus of the tube (D8). The tubal car-tilage(D24) leaves open a cleft that is linedby connective tissue (membranous lamina). The tendon of the tensor tympani muscle
(D9) attaches to the base of the manubrium of the malleus. The tympanic cavity communicates with the pharyngeal cavity through the auditory tube, thus per-mitting exchange of air and the equilibra-tion of pressure in the middle ear. The open-ing of the auditory tube, however, is nor-mally closed and opens only when the pharyngeal muscles contract (swallowing).
The internal ear consists of the bony laby-rinth (D10), which contains the mem-branous labyrinth and the internal acoustic meatus.