The middle ear is the part of the ear that is internal to the eardrum, external to the inner ear’s oval window.. Found in mammals the middle ear has three ossicles, a hollow space in the middle ear called the tympanic cavity. The tympanic cavity is joined to the nasal cavity by the eustachian tube.
Blausen.com staff. “Blausen gallery 2014”. Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762.
The middle ear’s main function is to transfer acoustic energy from waves of compression in the air to membrane waves in the cochlea’s fluid. Other animals have different middle ears that evolved. Early fossil tetrapods, reptiles, and birds possessing a single auditory ossicle, the columella, that connected with the eardrum directly and operating as a evolutionary derivative of a bone in fish ancestors called the “hyomandibula”, which supported the skull as well as brain case. Mammals have a unique middle ear with three ossicles that evolved independently of the single ossicle middle ears that other land vertebrate possessed during the Triassic period.
The middle ear has three small bones called the ossicles. They are the malleus, the incus, and the stapes. They were given their Latin names according to their distinctive stapes. They are also known as the hammer, the anvil, and the stirrup. These ossicles mechanically convert the energy and vibrations in the ear drum and transfer sound energy from the ear drum to the cochlea’s oval window, where it becomes amplified pressure waves in the inner ear’s fluid using the hydraulic and lever principle..
The middle ear also contains two tiny muscles. The tensor tympani muscle is attached to the hammer and helps tune and protect the ear. The stapedius muscle is attached to the stirrup. This muscle contracts in response to a loud noise, making the chain of ossicles more rigid so that less sound is transmitted. This response, called the acoustic reflex, helps protect the delicate inner ear from sound damage.
The malleus is merged with the eardrum and connects to the incus. The incus then connects to the stapes. The eardrum attaches to the malleus handle and the linear attachment smooths out chaotic motion at frequencies that are three kHz or higher, allowing the ear to respond over a wider frequency change linearly than with a point attachment. The malleus or hammer on the inside moves when sound makes the eardrum vibrate.
The incus connects to the stapes and the malleus. It pushes against the incus, or anvil during eardrum vibrations and the incus sends movements to the stapes.
The incus connects to the stapes, or stirrup, where their vibrations introduce pressure waves to the inner ear. Then the stapes push on the inner ear’s fluid through the oval window of the cochlea.
The Tympanic Cavity
This is the hollow space in the middle ear, also known as the cavum tympani. This is a small cavity that surrounds the middle ear’s bones. It is separated by the eardrum and abuts the external auditory meatus.
The Eustachian Tube
This tube helps to join the tympanic cavity to the nasal cavity, the airway at the nose’s back(the nasopharynx). This lets the pressure between the middle ear and the throat equalize and allows outside air to come in behind the eardrum in the middle ear. The eustachian tube opens when you swallow and helps maintain equal pressure on either side of the ear drum as well as preventing fluid from accumulating. The eardrum can uncomfortably retract or bulge if pressure isn’t equal and in the process, distort hearing. Popping of the ears can relive ear drum pressure caused by sudden changes.
The Stapedius and Skeletal Muscles
These muscles may stiffen the ossicles’ movement. The stapedius is the smallest skeletal muscle the body has. It connects tot he scapes at the malleus’ base and is controlled by the medial pterygoid nerve. These muscles contract when they hear loud sounds which reduces the sound traveling to the inner ear. This process is called the Tympanic or acoustic reflex.