Tympanic Membrane

 TYMPANIC MEMBRANE 

This is a thin, translucent partition between the external acoustic meatus and the middle ear.
It is oval in shape,
measuring 9 x 10 mm. 

It is placed obliquely at an angle of 55 degrees with the floor of the meatus.
It faces downwards, forwards and laterally
The membrane has outer and inner surfaces.
The outer surface of the membrane is lined by thin skin. 

It is concave.
The inner surface provides attachment to the handle of the malleus which extends up to its centre. 

The inner surface is convex.
The point of maximum convexity lies at the tip of the handle of the malleus and is called the umbo. 

The membrane is thickened at its circumference which is fixed to the tympanic sulcus of the temporal bone on the tympanic plate.
Superiorly, the sulcus is deficient.
Here the membrane is attached to the tympanic notch.
From the ends of the notch, two bands, the anterior and posterior malleolar folds, are prolonged to the lateral process of the malleus.
While the greater part of the tympanic membrane is tightly stretched and is, therefore, called the pars tensa, 

the part between the two malleolar folds is loose and is called the pars flaccida.
The pars flaccida is crossed internally by the chorda tympani 

This part is more liable to rupture than the pars tensa. 

The membrane is held tense by the inward pull of the tensor tympani muscle which is inserted into the upper end of the handle of the malleus. 

Structure 

The tympanic membrane is composed of the
following three layers: 

1. The outer cuticular layer of skin.
2. The middle fibrous layer made up of superficial radiating fibres and deep circular fibres.
The circular fibres are minimal at the centre and maximal at the periphery.
The fibrous layer is replaced by loose areolar tissue in the pars flaccida.
3. The inner mucous layer is lined by a low ciliated columnar epithelium. 

Blood Supply 

1. The outer surface is supplied by the deep auricular branch of the maxillary artery.
2. The inner surface is supplied by the anterior
tympanic branch of the maxillary artery and by the posterior tympanic branch of the stylomastoid branch of the posterior auricular artery.

Venous Drainage 

Veins from the outer surface drain into the external jugular vein.
Those from the inner surface drain into the transverse sinus and into the venous plexus around the auditory tube. 

Lymphatic Drainage 

Lymphatics pass to the preauricular and retropharyngeal lymph nodes. 

Nerve Supply 

I. Outer surface: The anteroinferior part is supplied by the auriculotemporal nerve, and the posterosuperior part by the auricular branch of the vagus nerve with a communicating branch from facial nerve.
2 Inner surface: This is supplied by the tympanic branch of the glossopharyngeal nerve through the tympanic plexus 

Clinical Anatomy 

For examination of the meatus and tympanic membrane, the auricle should be drawn upwards, backwards and slightly laterally.
However, in infants, the auricle is drawn downwards and backwards because the canal is only cartilaginous and the outer surface of the tympanic membrane is directed mainly downwards 

Boils and other infections of the external auditory meatus cause little swelling but are extremely painful, due to the fixity of the skin to the 

underlying bone and cartilage. 

Ear should be dried after head bath or swimming.
Irritation of the auricular branch of the vagus in the external ear by ear wax or syringing may reflexly produce persistent cough called eat cough, vomiting or even death due to sudden cardiac inhibition.
On the other hand, mild stimulation of this nerve may reflexly produce increased appetite.
Accumulation of wax in the external acoustic meatus is often a source of excessive itching,although fungal infection and foreign bodies should be excluded.
Troublesome impaction of large foreign bodies like seeds, grains, insects is common.
Syringing is done to remove these
Involvement of the ear in herpes zoster of the geniculate ganglion depends on the connection between the auricular branch of the vagus and the facial nerve within the petrous temporal bone. 

Small pieces of skin from the lobule of the pinna are commonly used for demonstration of lepra bacilli to confirm the diagnosis of leprosy.
Pinna is used as grafting material.
Hair on pinna in male represents y-linked inheritance. 

Infection of elastic cartilage may cause perichondritis.
Bleeding within the auricle occurs between the perichondrium and auricular cartilage.
If left untreated fibrosis occurs as haematoma compromises blood supply to cartilage. Fibrosis leads to "cauliflower ear". It is usually seen in wrestlers.
Tympanic membrane is divided into an upper smaller sector, the pars flaccida bounded by
anterior and posterior malleolar folds and a larger sector, the pars tensa. 

Behind pars flaccida lies the chorda tympani, so disease in pars flaccida should be treated carefully 

When the tympanic membrane is illuminated for examination, the concavity of the membrane produces a 'cone of light’ over the anteroinferior quadrant which is the farthest or deepest quadrant with its apex at the umbo. 

Through the membrane, one can see the underlying handle of the malleus and the long process of the incus.
The membrane is sometimes incised to drain pus present in the middle ear.
The procedure is called myringotomy. 

The incision for myringotomy is usually made in the posteroinferior quadrant of the membrane where the bulge is most prominent.
In giving an incision, it has to be remembered that the chorda tympani nerve runs downwards and forwards across the inner surface of the membrane, lateral to the long process of the incus, but medial to the neck of the malleus. 

If the nerve is injured taste from most of anterior two thirds of tongue is not perceived. Also salivation from submandibular and sublingual glands gets affected. 

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Tympanic Membrane | Situation | Parts | Recess | Layers | Development | Deep Relations |Blood Supply