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Tympanic membrane is a thin, semi-transparent, oval shaped membrane that separates the external ear from the middle ear. The tympanic Membrane’s main function is to assist in human hearing. The membrane vibrates with the force of a sound wave strike and transmits the vibrations further into the bones of the middle ear. Despite the diminutive size and mass, tympanic membrane is extremely tough and flexible, and difficult to damage beyond repair.
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Key Terms: Tympanic Membrane, Eardrum, Anatomy of Human Ear, Perforation
Tympanic Membrane
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It is a thin, circular layer of tissue that marks the point between the middle ear and the external ear. It is approximately 0.1 mm thick, 8 to 10 mm in diameter, and has a mass weight of around 14 mg. Tympanic Membrane lies across the end of the external canal and looks like a flattened cone with its apex pointed inward. The edges of the membrane are attached to a ring of bone, the tympanic annulus.
As shown in the figure it separates External acoustic meatus from Tympanic cavity. It is positioned at the lateral end of the external acoustic meatus and is oriented obliquely in the anteroposterior, mediolateral and superoinferior planes. Consequently, its superoposterior end lies lateral to its anterior inferior end.
Working of Tympanic Membrane
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The tympanic membrane, also called the eardrum, is a flexible, diaphragm-like structure. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal (external auditory meatus), which leads to tympanic membrane. The membrane moves synchronously in response to variations in air pressure, which constitute sound waves.
The sound waves then transmitted to ossicles inside the middle ear by tympanic membrane, and then to the oval window in the fluid-filled cochlea. Hence, it ultimately converts and amplifies vibration in air to vibration in cochlear fluid.a
Parts of Tympanic Membrane
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Subdivisions
The Tympanic Membrane is divided into two general parts by malleolar folds: the pars flaccida and the pars tensa.
- Pars flaccida: The relatively fragile pars flaccida lies above the lateral process of the malleus between the notch of rivinus and the anterior and posterior malleolar folds. It consists of the two Layers which appear slightly pinkish in hue. It is small, triangular and lax and is also called sharpnell’s membrane.
- Pars tensa: The larger part Pars Tensa consists of three layers, skin, fibrous tissue and mucosa. Its thick periphery forms a fibrous cartilaginous ring called annulus tympanicus or Gerlach’s ligament. While the central umbo tents inward at the level of the tip of malleus. The middle fibrous layer contains a radial, circular and parabolic fibre that encloses the handle of malleus.
Surfaces
Tympanic membrane is presented with two surfaces:
- Lateral Surface: It is concave towards the malleus and is directed downwards, forwards and laterally.
- Medial Surface: It is convex towards the middle ear and provides attachment to the handle of the malleus which extends up to its centre. The point of maximum convexity is called umbo.
Umbo
The manubrium of the malleus is firmly attached to the medial surface of the tympanic membrane as far as its centre, drawing it toward the tympanic cavity, and it pulls its anterior and inferior portion medially giving it a conical shape. The central point of maximum depression is called the Umbo and it marks the end of manubrium.
Cone of Light
When the tympanic membrane is illuminated on inspection, the concave of the membrane produces the cone of light radiating from umbo over the antero-inferior quadrant.
It receives attachment of the handle of the malleus up to the centre of the membrane.
Structure of Tympanic Membrane
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The Tympanic Membrane consists of three layers, a thin sheet of connective tissue covered by epithelium on both sides.
- Outer cuticle layer: Its lateral (outer) surface is covered by a thin epidermis, i.e., stratified squamous keratinized epithelium that is continuous with the epidermis of the external acoustic meatus.
- Intermediate fibrous layer: It is made up of fibroelastic connective tissue and contains the blood vessels and nerves of the Tympanic Membrane. The tympanic membrane is well supplied with blood due to blood vessels and it is extremely sensitive to pain because of its sensory nerve fibres. The fibrous layer is thickened at the edge of the inferior part of the tympanic membrane, forming a tough ligamentous ring, with which the tympanic membrane is lodged into the tympanic sulcus on the temporal bone.
- Inner mucous layer: It is covered by a simple cuboidal epithelium that is continuous with the epithelium of the mucous membrane of the tympanic cavity.
Nerve Supply
Sensation of the outer surface of the tympanic membrane is supplied mainly by the auriculotemporal nerve, a branch of the mandibular nerve, with contributions from the auricular branch of the vagus nerve, the facial nerve and possibly the glossopharyngeal nerve. The inner surface of the tympanic membrane is innervated by the glossopharyngeal nerve.
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Muscles
- There are no direct muscle attachments to the Tympanic Membrane. However, the tensor tympani muscle can pull the malleus inward to increase the tension across the membrane, effectively stiffening it. This involuntary activity is a part of the acoustic reflex, which protects the tympanic membrane and the cochlear apparatus from acoustic, vibration trauma precipitated by very loud sounds, including the sounds of chewing and talking.
- The stapedius muscle completes this reflex by retracting the stapes from the oval window to avoid damaging the cochlea with high-amplitude vibrations.
- The acoustic reflex requires approximately 40 milliseconds to take effect. Thus it is ineffective against very sudden loud sounds, for example, a gunshot.
Tympanic Membrane Damage
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The hole or tear in the membrane can rupture the tympanic membrane or eardrum. The membrane gets vibrated when the sound waves enter the eardrum and it travels to the middle ear. The ruptured membrane is also known as the perforated eardrum. Sometimes this may cause permanent loss of hearing.
Normal right Tympanic Membrane and Ruptured Tympanic Membrane
Other causes of hearing loss are:
- Infection: In children, the common cause for the rupture of the membrane is an infection, during which some fluid gets accumulated at the back of the tympanic membrane. This build up fluid can increase the pressure that leads to breaking in the tympanic membrane.
- Pressure Changes: Barotrauma occurs when the pressure that is present inside the ear is different from that pressure that is present outside of the ear. These changes in the pressure can lead to damage to the tympanum ear damage. Some of the activities can cause barotraumas that include driving at high altitudes, scuba diving, shock waves and forceful or direct impact to the ear.
- Injury: Another cause that can lead to the damage of the membrane is injury, the injury that occurs to the ear or sides of the head can cause damage to the eardrum. The injury can occur due to car accidents, getting hit to the ear, falling on the ear or injury during sports. Inserting any objects such as a pen, fingernail or cotton swab can harm the tympanic membrane.
Read Also: Infectious diseases: Types, symptoms and treatments
Symptoms and Treatment
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The main symptom is pain, watery blood or fluids filled with pus can drain from the infected or damaged ear. The damage that occurs to the middle ear can cause bleeding. The infections to the ear can be found in young children, people living in poor air quality or with cold or flu.
Treatments given to the ruptured ear are as follows:
- Patching: If the ear does not get repaired by itself then the doctor might suggest patching the tympanic membrane. It involves placing a medicated paper patch on the tear. This patch helps the membrane to grow back.
- Antibiotics: It helps to clear the infections and also helps to prevent getting infected by the new infections. The medical advisor can suggest oral antibiotics or some medicated ear drops.
- Surgery: Sometimes surgery is required to patch the hole present in the eardrum. The surgical repair of the membrane is known as tympanoplasty. This is done by grafting the hole with the tissue taken from another part of the body.
Along with these treatments some home remedies can help to relieve the pain such as placing warm and dry compress on the ear can reduce the pain.
Things to remember
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- Two main functions of the tympanic membrane are auditory and protective.
- The tympanic membrane is the thin, flexible and circular layer which is approximately 0.1 mm thick, 8 to 10 millimetre in diameter, mass weight around 14 mg and it lies horizontally at an angle of 55.
- In the case of children, the tympanic membrane is more horizontal compared to adults and its advantage is that they withstand even loud noisy sounds.
- Tympanic membrane serves as the lateral wall of the tympanic cavity.
- Pars flaccida is more liable to rupture than pars tensa.
- Patients suffering from tympanic membrane ruptures rarely require medical intervention as between 80 to 95 percent of ruptures recover completely within two or four weeks itself.
- The absence of a cone of light in the Tympanic membrane does not necessarily signify an ear disorder, as it could be due to slope of the membrane or the shape of the ear canal.
Sample Questions
Ques. What are the two main subdivisions of tympanic membrane? (1 marks)
Ans. There are two main subdivisions of tympanic membrane pars flaccida and pars tensa.
Ques. Which part of the tympanic membrane is more liable to rupture? (1 marks)
Ans. Pars flaccida is more liable to rupture as it is comparatively more fragile than pars tensa.
Ques. Is cochlea responsible for balance? (1 marks)
Ans. No, cochlea is not responsible for balance, it is responsible for hearing.
Ques. Pars tensa consists of three layers? (1 marks)
Ans. Pars Tensa consists of three layers, skin, fibrous tissue and mucosa.
Ques. Where does the tympanic membrane be positioned at? (1 marks)
Ans. Tympanic membrane is positioned at the lateral end of the external acoustic meatus.
Ques. Explain the function of Tympanic Membrane? (2 marks)
Ans. Main function of the Tympanic Membrane is to assist in hearing. It separates the outer ear from the middle ear. When sound waves reach the tympanic membrane they cause it to vibrate. The membrane moves synchronously in response to variations in air pressure, which constitute sound waves. The vibrations are then transferred to the tiny bones in the middle ear.
Ques. What is tympanic membrane? (2 marks)
Ans. A thin, semitransparent membrane that separates the outer ear and the middle ear is known as tympanic membrane. It is also known as eardrum. Tympanic membrane receives sound from the outer ear and passes it to the middle ear.
Ques. What do you understand by umbo? (3 marks)
Ans. The manubrium of the malleus is firmly attached to the medial surface of the tympanic membrane as far as its centre, drawing it toward the tympanic cavity, and it pulls its anterior and inferior portion medially giving it a conical shape. The central point of maximum depression is called the Umbo.
Ques. What is meant by perforation? What are the reasons for perforated tympanic membrane? (3 marks)
Ans. A tympanic membrane perforation is a hole or tear in the thin tissue that separates the ear canal from the middle ear.
Some of the reasons that cause perforations are middle ear infection, barotraumas, loud sounds or blasts, foreign objects in the ear and severe head trauma. Middle ear infection results in the accumulation of fluids in the middle ear, pressure from these fluids can rupture the eardrum.
Barotrauma is a stress forced on the tympanic membrane. It occurs when the air pressure in the middle ear and air pressure in the external environment is not in balance.
Ques. Explain three layers of tympanic membrane? (3 marks)
Ans. Tympanic membrane consists of three layers,
- Outer cuticle layer: Its lateral surface is covered by a thin epidermis, i.e., stratified squamous keratinized epithelium that is continuous with the epidermis of the external acoustic meatus.
- Intermediate fibrous layer: It is made up of fibroelastic connective tissue and contains the blood vessels and nerves of the Tympanic Membrane. The tympanic membrane is well supplied with blood due to blood vessels and it is extremely sensitive to pain because of its sensory nerve fibres. The fibrous layer is thickened at the edge of the inferior part of the tympanic Membrane.
- Inner mucous layer: It is covered by a simple cuboidal epithelium that is continuous with the epithelium of the mucous membrane of the tympanic cavity.
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