The Anatomy of the Middle Ear
Before you get started, take a look at our Anatomy of the Ear post to get a general understanding of the different parts of the ear.
The main function of the middle ear is to transmit vibrations from the eardrum. The eardrum separates the middle ear from the outer ear and turns sound waves from our environment into vibrations that are transmitted to the inner ear through the auditory ossicles, the three smallest bones in our bodies.
Parts of the Middle Ear
The middle ear can be organized into two parts:
The tympanic cavity: This contains the auditory ossicles which consist of three small bones – the malleus, incus, and stapes.
The epitympanic recess: This is located above the tympanic cavity containing the head of the malleus and the body of the incus.
Bones of the Middle Ear
As we mentioned earlier, the auditory ossicles in the middle ear contain the malleus, incus, and stapes. The ossicles transmit vibrations from the tympanic membrane through these small bones, which are connected in a chain, to the oval window of the inner ear where fluids will move and excite receptors. This process allows sound to be transformed into electrical signals which are then sent to the brain.
The movement created from sound vibrations in the tympanic membrane helps transmit those sound waves from the tympanic membrane to the oval window of the inner ear. The malleus, the largest ear bone, is connected to the tympanic membrane and transmits those sound waves to the incus. From the incus, the sound waves are then transmitted to the stapes, which is the smallest bone in the body and is also connected to the oval window.
Roof: The roof is a thin bone from the temporal bone that separates the middle ear from the middle cranial fossa.
Lateral wall: This wall consists of the lateral wall of the epitympanic recess and the tympanic membrane.
Medial wall: The medial wall separates the middle ear from the inner ear, and also contains the oval window.
Anterior wall: The anterior wall, formed by a thin plate, separates the middle ear and the internal carotid artery and contains two openings. One for the auditory tube and the other for tensor tympani muscle.
Posterior wall: The posterior wall, also known as the mastoid wall, is made up of a partition between the tympanic cavity and the mastoid air cells.
Floor: The floor, also known as the jugular wall, is formed by a thin layer of bone that separates the middle ear from the internal jugular vein.
Muscles of the Middle Ear
There are two muscles in the middle ear. The tensor tympani and the stouter muscle that protects the ear from loud noises.
The tensor tympani, the longer of the two muscles, connects to the malleus bone and serves to moderate loud sounds, such as yelling. To protect the middle ear from these loud noises, the tensor tympani contracts, pulling the malleus inward and maintaining or increasing the tension of the tympanic membrane.
The stouter muscle, also called the stapedius, reduces the intensity of sounds, often times lower frequency sounds, that enter the inner ear. This smaller muscle is attached to the stapes and is more sensitive to sound than the tensor tympani.
The eustachian tube controls the air pressure maintaining a balance between the air pressure inside the ear and the air pressure outside of it. This tube connects the back of the nose and the upper throat to the middle ear.
Thank you for reading about the anatomy of the middle ear. We hope this article was helpful in showcasing the middle ear anatomy and how it helps us hear and balance.
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