The middle ear is located in the petrous part of the temporal bone, includingTympanic membraneThe medial tympanic chamber and the supratympanic recess above the tympanic membrane.The pharyngeal cavity is opened through the eustachian tube in the front, and the mastoid chamber is opened through the mastoid sinus in the upper rear. The tympanic chamber is covered with mucosa, which is connected with the eustachian tube and the mucosa of the mastoid chamber.The contents of the middle ear are as follows: auditory ossicles: malleus, incus and stapes;Stapes muscle and tensor tympani muscle;Chorda tympani nerve (a branch of facial nerve);Plexus tympani.Scientists reveal that the human middle ear was once the gill of fish。[1]
The tympanum is prismatic or long and narrow box shaped, with concave edges, one bottom, one top and four walls.
At the top is a thin bone plate, namely the tympanic lid, which separates the dura mater and tympanic chamber of the middle cranial fossa;The bottom (wall of the jugular vein) is a thin bone plate that separates the tympanic chamber from the superior jugular bulb;The outer (membranous) wall is almost all formed by the depressed tympanic membrane. The upper part is the bone plate of the superior recess of the tympanic chamber. The tympanic membrane wraps around the handle of the malleus, and the malleus head is located in the superior recess of the tympanic chamber;The medial (labyrinth) wall separates the middle ear from the inner ear, and the protrusions formed at the base of the cochlea can be seen;The anterior wall (carotid artery wall) separates the tympanic chamber from the carotid artery tube, and its upper part is the opening of the eustachian tube and the myenteric tube;On the upper part of the posterior wall (mastoid wall), there is a mastoid sinus opening to the mastoid chamber, connecting the tympanic chamber and the mastoid process. The facial nerve canal is located inside the mastoid sinus opening, and the mastoid chamber descends from the posterior wall of the tympanic chamber.
The mastoid sinus is located in the mastoid process of the temporal bone. Like the tympanic chamber, the top is separated from the middle cranial fossa by the tympanic lid, and the bottom passes through the mastoid chamber through a small hole.Mastoid sinus and mastoid chamber are covered with mucosa, which is adjacent to middle ear mucosa, and adjacent to facial nerve canal in front of mastoid sinus.
Eustachian tube
The eustachian tube connects the tympanic chamber and the nasopharyngeal cavity. It opens backward and downward in the lower nasal meatus of the nasal cavity. The posterior outer 1/3 is osseous, and the rest is cartilaginous.The eustachian tube is covered with mucosa, which is connected with the mucosa of the tympanic chamber backwards and the mucosa of the nasopharynx forwards.
The air can enter and exit the tympanic chamber freely through the eustachian tube, balance the pressure of the tympanic chamber and the outside world, and ensure the free movement of the tympanic membrane.Under normal circumstances, the eustachian tube wall formed by the cartilage stent is attached together, so the eustachian tube can be opened actively only when the levator veli palatini contracts and pulls one side of the eustachian tube and the tensor veli palatini contracts and pulls the other side of the eustachian tube.These are soft palate muscles, so yawning and swallowing are often used to balance the pressure on both sides of the eardrum.
The ascending pharyngeal artery (one of the branches of the external carotid artery), the middle meningeal artery and the pterygoid artery, branches of the maxillary artery, are distributed in the eustachian tube.The tympanic plexus formed by the facial nerve and the glossopharyngeal nerve issued branches to the eustachian tube, and nerve fibers from the pterygopalatine ganglion also innervate the eustachian tube.
Auditory ossicle
The ossicles in the tympanic chamber form an ossicular chain from the tympanic membrane to the oval window, which is an oval opening on the inner wall of the tympanic chamber, closed by the bottom of the stapes, and connects with the inner ear bone labyrinth.The ossicles of auditory ossicles are the earliest in the development process. They are fully mature at birth, and hard and dense.The malleus is attached to the tympanic membrane, the stapes are attached to the oval window, and the incus is between the two bones, forming joints with them respectively.The auditory ossicle is different from other bones in that it covers the mucosa of the tympanic chamber, not the periosteum.
Malleus
The mallet head is round, located in the upper recess of the tympanic cavity, the neck is located below the relaxed part of the tympanic membrane, the handle is surrounded by the tympanic membrane, and the tip of the handle is located at the umbilicus of the tympanic membrane, and moves together with it.The malleus head and the incus joint, the tendon of the tensor tympanic membrane inserted the malleus handle near the malleus head, the chorda tympani nerve crossed the inner surface of the neck of the malleus, and the malleus played a leverage role through the long protrusions and the handle attached to the tympanic membrane.
Incus
The incus body is large, located in the superior recess of the tympanic chamber, and is connected with the malleus head. The long leg is parallel to the handle of the malleus. The medial end is connected with the stapes through the lenticular process that processes outward. The short leg of the incus is attached to the posterior wall of the tympanic chamber through ligaments.
Stapes
The stapes are the smallest auditory ossicles. The head of the stapes is connected to the bottom of the stapes through the front and rear feet, and the latter is attached to the oval window on the inner wall of the tympanic chamber.The area of stapes bottom is much smaller than that of tympanic membrane. Through this process, the vibration force is amplified by more than 10 times. Therefore, the role of listening to small bones is to amplify the vibration force of tympanic membrane transmitting sound waves and reduce the amplitude.
