Get To Know The Mind-blowing Anatomy Of The Middle Ear
As we dealt with the anatomy of the outer ear in the previous blog, lets talk about middle ear now! The middle ear is a cavity within the petrous part of temporal bone. It is approximately a cubical box with its walls formed by bone which is lined by mucosa.
The middle ear cleft is a diverticulum developed from the naso-pharynx in the embryonic life which later develops into middle ear, auditory tube or eustachian tube, the aditus which leads to a large cavity the mastoid antrum. The mastoid antrum is the air-filled space within the mastoid process.
The anatomy of the middle ear is usually discussed as its walls and the contents of middle ear. It is to be mentioned that all the walls and its contents originating from the walls is also covered by the same mucosa. So the middle ear is said to be a mucus lined cavity meaning between the mucosa of its contents and between the mucosa of its walls present is only air.
As mentioned, the middle ear is a cubical box connected to the eustachian tube and the aditus contains 6 walls – the anterior wall, the posterior wall, the roof, the floor, the lateral wall and the medial wall. The middle ear is surrounded laterally by the outer ear and medially by the inner ear.
The Lateral Wall – Formed by the tympanic membrane and from it originates the long process of malleus. The chorda tympani nerve, branch of fascial nerve(7th cranial nerve) also forms a part lies between the handle of malleus and long process of incus. The malleus and incus are the middle ear ossicles which are to be discussed in middle ear contents.
The tympanic membrane divides the middle ear into epitympanum(middle ear cavity above the tympanic membrane), the hypotympanum(middle ear cavity below the tympanic membrane) and the mesotympanum(cavity between epi- and hypo-tympanum).
- Separates the cavity from the middle cranial fossa.
- Formed by a thin piece of bone called tegmen tympani.
- The roof also extends to cover the aditus and antrum
- Separates the cavity from the jugular bulb formed by the internal jugular vein.
- The floor is also called as Jugular wall, lies along the jugular foramen at the base of the skull.
- The floor is pierced by the tympanic branch of 9th cranial nerve
The Posterior Wall
- Partially Separates the cavity from mastoid antrum
- The aditus is a small canal lies in the epitympanum which connects the mastoid antrum and the cavity. It also separates the cavity from the fascial nerve which runs vertically downwards below the epitypanum and behind the posterior wall.
- The nerve forms what is called fascial canal over the posterior wall. From this canal, a small aperture called the posterior canalicus, from which the chorda tympani arises.
- The posterior wall also posses a small bony projection called pyramid, within the projection lies the stapedius muscle and from the tip of the projection the tendon of stapedius arises.
The Anterior Wall
- The lower part of the anterior wall forms the boundary of carotid canal through which the internal carotid artery(vessel supplying the brain).
- The upper part contains the fossa for tensor tympani muscle and below it lies the opening for auditory tube.
The Medial Wall
- Separates the cavity from the inner ear and the fascial nerve which has an oblique course behind the medial wall
- This forms a bony prominence in the wall called the oblique part of fascial canal which then descend vertically downwards along the posterior wall.
- Contains the round and oval window of inner ear, the promontory and sinus tympani.
- The sinus tympani is a small depression between the round and oval windows which indicates the position of ampulla of posterior semicircular canal(structure of inner ear).
- The promontory is a round bulge prominence separating the cavity from the first turn of cochlea(structure of inner ear).
- The promontory contains the tympanic plexus of nerve which is contributed by the tympanic branch of glossopharyngeal nerve(the structure which pierces the floor of the cavity).
- The processus cochleariformis is a bony prominence which lies in the medial wall, formed as a extension of the bone between the 2 openings in the upper part of anterior wall.
Thus from this blog, we came to know about the mind-blowing anatomy of the middle ear!
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