Generality
The eardrum, or tympanic membrane, is the thin, transparent and oval-shaped membrane, which lies between the outer ear and the middle ear, and which guarantees the passage of sounds from the external auditory canal to the three ossicles.
Despite its small size, the tympanum is a very resistant and finely innervated structure. Among the nerve structures that innervate the eardrum, there are: the auriculotemporal nerve, the tympanic cord, the auricular branch of the vagus nerve and the tympanic nerve.
The eardrum can be subject to breaks / perforations and some morbid conditions, such as the cholesteatoma.
Short review of the ear and its compartments
The ear is the organ of hearing (allows the perception of sounds) and of balance (guarantees static and dynamic balance).
The anatomists typically divide it into three compartments, which they call: external ear, middle ear and inner ear .
The outer ear is the part of the ear visible to the naked eye, on the sides of the head. The middle ear is the part of the ear between the outer ear and the inner ear. Finally, the inner ear is the deepest part of the ear.
The ear includes portions of cartilaginous nature, bones, muscles, nerves, blood vessels, sebaceous glands and ceruminous glands.
What is the eardrum?
The eardrum, or tympanic membrane, is the thin, transparent and oval-shaped membrane that ideally separates the middle ear - of which it is one of the main components - from the outer ear.
The eardrum is an element of the fundamental ear to the mechanism of perception of sounds.
MIDDLE EAR: BEYOND THE TIMPANO WHAT DOES IT INCLUDE?
Before proceeding with the anatomical and functional description of the eardrum, it is necessary to review the middle ear and its constituent elements.
In addition to the tympanic membrane, the middle ear includes:
- The tympanic cavity, in which the so-called three ossicles lodge. Known by the names of hammer, anvil and stirrup, the three small bones of the middle ear play a decisive role in the process of perception of sounds.
- The Eustachian trumpet . Also known as the auditory tube, it connects the middle ear with the pharynx and the air cells of the mastoid.
- The oval window and the round window . They are two membranes very similar to the eardrum, whose job is to transmit sound vibrations from the middle ear to the inner ear.
| Table. Ear compartments and their components (the middle ear is excluded). | |
| Ear compartment | Components |
| External ear |
|
| Inner ear |
|
Anatomy
The eardrum resides at the end of the external auditory canal (component of the external ear) and immediately before the tympanic cavity .
Able to communicate with the hammer (one of the three small bones of the middle ear), the eardrum remains fixed in position, thanks to a circular cartilaginous structure, in the middle-lower part, and ligaments, in the upper part.
- The circular cartilaginous structure is known as tympanic ring, tympanic or tympanic anulus . The tympanic ring guarantees the fixing of the mid-lower part of the eardrum, through its insertion in the so-called tympanic bone .
- The ligaments that fix the upper portion of the eardrum anchor the latter to the temporal bone . In anatomy, these ligaments are called tympanic-malleolar ligaments .
On the tympanum, anatomists generally recognize two regions, whose names are: pars tensa and pars flaccida .
- The pars tensa is the most important region by extension and importance. Located in the middle-lower part, it derives from the superposition of three layers of different tissue: the outermost tissue layer is of a cutaneous nature, the intermediate tissue layer is of a fibrous nature (it contains collagen fibers) and, finally, the innermost tissue layer is of mucous nature.
Robust and resistant, the pars tensa presents, almost in a central position, a particular structure, called umbo or navel . The umbo represents the structural element of the tympanic membrane, which allows communication between the latter and the handle of the hammer, during the process of perception of sounds.
The aforementioned tympanic ring takes place all around the pars tensa .
- The pars flaccida is a small region of reduced extension and triangular shape, located in the upper part of the eardrum.
Unlike the pars tensa, it lacks the layer of fibrous tissue; therefore it is the result of the superposition of only two different tissue layers: the layer of skin tissue and the layer of mucous tissue.
The pars flaccida is in close contact with the already mentioned tympanic-malleolar ligaments.
TIMPANO MEASURES
Generally, the eardrum has:
- A thickness of 0.1 millimeters;
- A diameter between 8 and 10 millimeters;
- A weight not exceeding 14 milligrams.
Despite its small thickness and small size, the eardrum is extremely resistant, flexible and difficult to damage beyond repair.
INNERVATION
The innervation of the eardrum belongs to different nerves, including: the auriculotemporal nerve, the so-called tympanic cord, the auricular branch of the vagus nerve and the tympanic nerve .
Going further into details:
- The auricolotemporal nerve is the nerve structure responsible for the innervation of a large part of the external surface (or lateral surface) of the eardrum.
- The tympanic chord is a sensitive branch of the facial nerve (VII cranial nerve), whose task is to support the auricolotemporal nerve in the innervation of the external surface of the tympanum.
- The auricular branch of the vagus nerve has sensitive functions and also contributes to the innervation of the external surface of the tympanic membrane.
- The tympanic nerve, also known as Jacobson's nerve or tympanic branch of the glossopharyngeal nerve, is the nerve deputed to the innervation of the inner surface (or medial surface) of the eardrum.
Note: the surface of the tympanum facing the external auditory canal and the auricle is defined externally; instead, the tympanic surface facing the tympanic cavity and the deeper structures of the ear (cochlea and vestibular apparatus) is called internal.
Function
The ear participates in the perception of sounds with all three of its compartments. In fact, if the external ear represents the entry point of the sounds (or sound vibrations) inside the ear, the middle ear and the inner ear are the seats that, respectively, start and complete the fundamental process of transforming sounds into nerve signals / impulses, destined for the brain.
Within this framework, the tympanum acts as a vibratile membrane, which is activated when the sounds coming from the external auditory canal reach it.
Vibrating, the eardrum has the ability to set the hammer in motion, the first of the three ossicles of the ear (if you look at it from the side of the ear); the movement of the hammer triggers the anvil (the second of the three ossicles), which in turn drives the stirrup (the last of the three ossicles).
At this point, the sound vibrations pass from the bracket to the oval window and the round window, which have an operating mechanism very similar to the eardrum, ie they vibrate.
The vibration of the oval window and the round window is the trigger for the movement of the endolymph, a fluid contained in the cochlea, which is a fundamental component of the inner ear.
In the cochlear endolinfa, particular hair cells are dispersed, which together form the so-called organ of Corti ; with its movement, the cochlear endolinfa activates the organ of Corti, which, once in action, has the important function of transforming sounds into nerve signals / impulses.
In summary, therefore, the eardrum is the first element of the middle ear to come into action and represents the structure on which the passage of sounds from the external auditory canal to the three ossicles depends.
With the triggering of the three ossicles, the tympanic membrane initiates the process of transforming sounds into nerve signals / impulses.
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Figure : sound waves penetrate the outer ear and reach the eardrum. Struck by the sounds, the eardrum vibrates. This vibration is transmitted to the three ossicles, which set in motion. The hammer begins to move, then the anvil and, finally, the stirrup. In other words, the movement of a small bone determines the movement of the next one. It is the so-called ossicular chain.
From the bracket, the sound signal passes to the cochlea, through the window the oval and the round window. The cochlea translates the sound into a nervous signal, intended for the brain for final identification.
TIMPANO AS A PROTECTIVE BARRIER
In addition to participating in the perception of sounds, the eardrum also plays an important protective role in relation to the deeper compartments of the ear. In fact, it acts as a defensive barrier against those germs and bacteria capable of infesting the middle ear and the inner ear and causing dangerous infections against them.
Without the eardrum, the deeper elements of the human ear would be continuously exposed to contamination by pathogenic microorganisms.
Tympanic diseases
The eardrum can be the victim of morbid conditions that affect its functioning. Inadequate functioning of the eardrum leads to a reduction in the hearing ability of the person concerned.
Among the morbid conditions that can affect the eardrum, the episodes of rupture / perforation of the tympanic membrane and a pathology known as the cholesteatoma deserve a mention.
BREAKAGE / PUNCHING OF TIMPANO
With rupture / perforation of the eardrum, the doctors intend to tear the tympanic membrane .
Episodes of rupture / perforation of the eardrum can be the consequence of:
- An infection of the middle ear . Represents the main cause of rupture / perforation of the eardrum.
- A direct traumatic event . They can break / pierce the eardrum, the traumas to the ear deriving from: the practice of contact sports, a very strong slap, the accidental penetration of foreign bodies, the improper use of objects for cleaning the external auditory canal etc.
- A loud noise . An intense and sudden noise (eg: explosion of a bomb) can create shock waves that can damage the tympanic membrane.
- A sudden and violent change in air pressure ( barotrauma ). It is rare, but it can happen, when the middle ear is not able to adapt quickly to changes in external pressure.
From the symptomatological point of view, the tympanic rupture / perforation causes a reduction in hearing ability ( hypoacusis ) and, if the tear is sudden, an intense ear pain .
The rupture / perforation of the eardrum can represent, for germs and bacteria, a gateway to the deepest structures of the ear and lead to dangerous infections.
cholesteatoma
Cholesteatoma is a pathology of the middle ear, characterized by the unusual collection of epithelial cells near the eardrum and the three ossicles.
To cause the accumulation of epithelial cells typical of the cholesteatoma can be infections affecting the ear ( acquired cholesteatoma ) or an anomaly of the ear present since birth ( congenital cholesteatoma ).
The acquired cholesteatoma is far more widespread than the congenital cholesteatoma.
The main symptom of cholesteatoma is hypoacusis, moderate, in the early stages of the disease, and much more intense, in the advanced stages of the disease.
If left untreated, the cholesteatoma can damage the structures surrounding the eardrum and the three ossicles, further complicating the symptomatology and making recovery even more difficult.
As a rule, the treatment of the cholesteatoma is surgical and consists in the removal of abnormal epithelial cells, both from the tympanum and from the three ossicles.
If the cholesteatoma was at a very advanced stage, surgery could also include the replacement of the eardrum and the three ossicles with ad hoc prostheses.
