Tympanic membrane

At a glance

English

Tympanic membrane

Latin (TA2)

Membrana tympanica

System

Nerve

Region

Head

Side

Paired, left and right

About the tympanic membrane

The tympanic membrane closes off the deep end of the external acoustic meatus and forms most of the lateral wall of the tympanic cavity. It is roughly oval, about a centimetre across, and set obliquely, so that its upper and back part lies further out than its lower and front part. Around it lie the middle cranial fossa above, the parotid gland below, the temporomandibular joint in front and the ossicles and facial nerve behind.

Most of the membrane is the taut pars tensa, built of three layers: skin on the outside, a fibrous middle layer of radial and circular fibres, and mucosa facing the middle ear. Its thickened rim, the fibrocartilaginous annulus, sits in a groove of the tympanic bone. Above the malleus's lateral process is a small, lax region, the pars flaccida, which lacks the fibrous layer and is bounded by the anterior and posterior malleolar folds and the tympanic notch. The handle of the malleus is fixed to the inner surface down to the centre, pulling the membrane inwards so that, seen from outside, it is concave; its deepest point is the umbo.

Sound waves in the canal set the membrane vibrating. The malleus picks up this motion and the ossicular chain passes it to the stapes in the oval window, so that vibration in air becomes vibration in the fluid of the inner ear. The large area of the membrane relative to the stapes footplate concentrates the force and helps overcome the mismatch between air and fluid.

On otoscopy a healthy drum is pearly grey, with the handle of the malleus visible and a bright cone of light running forwards and downwards from the umbo. A perforation, from infection, a blast, diving or a pressure change when the auditory tube is blocked, causes conductive hearing loss and sometimes tinnitus or vertigo; most small tears heal on their own within weeks. A pars tensa perforation is more common, while retraction of the pars flaccida is linked to auditory tube dysfunction and cholesteatoma. When infected fluid builds up behind the drum, a small surgical incision (myringotomy), often with a ventilation tube, lets it drain.

Course and supply

Supplies

Vibrates with incoming sound and passes the motion to the malleus, beginning the conduction of sound through the middle ear to the cochlea.

Nerve supply

Outer surface mainly from the auriculotemporal nerve (V3), with the vagus nerve's auricular branch and small facial nerve twigs; inner surface from the glossopharyngeal nerve through the tympanic plexus.

Blood supply

Outer surface from the deep auricular artery; inner surface from the anterior tympanic artery and the stylomastoid branch of the posterior auricular artery.