What Is the Middle Ear?

The middle ear is located in the temporal bone, including the tympanic cavity inside the tympanic membrane and the tympanic recess above the tympanic membrane. The eustachian tube is used to pass through the pharyngeal cavity in the front, and the mastoid sinus ostium is used to pass through the mastoid small chamber. The contents of the middle ear are as follows: auditory ossicles: hammer, anvil and sacrum; stapedius and tympanic muscles; tympanic nerve (branch of facial nerve); tympanic nerve plexus.

Chinese name: Middle ear
Tympanum: In the temporal bone

Tympanic wall: Upper wall (cover wall): a thin layer of bone plate
Structure: There are 3 small ossicles, hammer, anvil and sacrum

Middle ear tissue

Middle ear tympanum wall

The tympanum is prismatic or elongated box-shaped, with recessed edges, a bottom, a top, and four walls.

The top is a thin layer of bone plate, the tympanic cap. The tympanic cover separates the dura mater and the tympanic cavity in the middle cranial fossa. The bottom (jugular wall) is a thin layer of bone plate, which separates the tympanic cavity and the superior jugular bulb. The wall is almost entirely formed by a recessed tympanic membrane. The upper part is the bone plate of the recess in the tympanum. The tympanum surrounds the malleolus stem. The hammer bone is located in the recess of the tympanum. The medial (laboratory) wall separates the middle ear and the inner ear. The base of the cochlea is visible. The anterior wall (carotid artery wall) separates the tympanic cavity and the carotid artery tube, and the upper part is the eustachian tube and the tympanic tensor myotube opening; the upper part of the posterior wall (mastoid wall) has a mastoid sinus opening through the mastoid small chamber, which connects The tympanic cavity and mastoid, the facial canal is located inside the mastoid sinus ostium, and the mastoid atrium and the posterior wall of the tympanum descend.

The mastoid sinus is located in the mastoid process of the temporal bone. Like the tympanum, the apical space and the middle cranial fossa are separated by a tympanic cap. Mastoid sinuses and mastoid sinuses are covered with mucous membranes, which are continuous with the middle ear mucosa and adjacent to the neural tube before the mastoid sinuses.

Eustachian tube

The eustachian tube connects the tympanic cavity and the nasopharyngeal cavity, and opens downwards to the lower nasal passage of the nasal cavity. The posterior outer 1/3 is bony and the rest is cartilage. The eustachian tube is covered with a mucous membrane, which is continuous with the tympanic mucosa in the backward direction and with the nasopharyngeal mucosa in the forward direction.

Air can freely enter and exit the tympanic cavity through the eustachian tube, and balance the pressure between the tympanic cavity and the outside world to ensure the free movement of the tympanic membrane. Under normal circumstances, the wall of the eustachian tube formed by the cartilage stent is attached together, so only when the levator laminalis muscle contracts and pulls one side of the eustachian tube, the sphincter muscle tightens and pulls the other side of the eustachian tube. The eustachian tube is actively opened. 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 branch of the maxillary artery. The tympanic plexus formed by the facial nerve and the glossopharyngeal nerve is distributed in the eustachian tube, and the nerve fibers from the pterygopalatine ganglion also dominate the eustachian tube.

Middle ear hearing bone

The auditory ossicles in the tympanum form the ossicular chain from the tympanic membrane to the oval window, which is an oval opening on the inner wall of the tympanum, closed by the base of the sacrum, and connected to the inner ear bone labyrinth. The ear bones were ossified during development. They were fully mature at birth and the ear bones were hard and dense. The hammer bone is attached to the tympanic membrane, and the sacrum is attached to the oval window. Between the two bones is the anvil bone, which forms a joint with them. The auditory ossicle is different from other bones in that it covers the tympanic mucosa, not the periosteum.

Middle ear malleus

The hammer bone is round, located in the recess of the tympanic cavity, the neck is located below the slack of the tympanic membrane, the stem is surrounded by the tympanic membrane, and the tip of the stalk is located at the umbilical cord and moves with it. The malleolus head and anvil joint, the tympanic membrane tendon is inserted near the malleolus head, the tympanic nerve crosses the inner surface of the malleolus neck, and the malleolus leverages through the long protrusions and the handle attached to the tympanic membrane.

Middle ear anvil

The anvil body is larger, located in the crypt above the tympanum. It is related to the malleolus head. The long foot is parallel to the malleolus stem. The medial end is connected to the sacrum by the lenticular process protruding to the outside. Back wall of tympanum.

Middle ear cheekbone

The sacrum is the smallest ossicle, and the sacrum head is connected to the bottom of the sacrum through the front and back feet, which is attached to the oval window on the inner wall of the drum chamber. The area of the base of the sacrum is much smaller than the area of the tympanic membrane. Through this process, the force of vibration is amplified by more than 10 times. Therefore, the role of the auditory ossicle is to amplify the vibrational force transmitted by the tympanic membrane to reduce the amplitude.