Anatomy · Eye, ear & senses

Tympanic membrane

The eardrum

Boundary between outer and middle ear

A thin, oval, semi-transparent, cone-shaped membrane about 9–10 mm across and 0.1 mm thick that closes the inner end of the external auditory meatus. Its middle is pulled inwards by the handle of the malleus, and it has three layers: skin outside, fibrous tissue in the middle and mucous membrane inside. Sound makes it vibrate, and the malleus carries the movement into the middle ear.

How to spot them

▸A pearly-grey, slightly translucent disc seen at the end of the ear canal through an otoscope
▸The handle of the malleus shows through as a whitish streak running from the top edge to the centre
▸A bright triangular cone of light reflects from its lower front part
▸Divided into a large taut part and a small, slack triangular part above

What to know

Its centre is dragged inwards by a bone attached to its inner surface, forming a point of greatest concavity seen from outside

The umbo of the tympanic membrane, created by the tip of the malleus handle

Seen through an otoscope, a bright triangle of reflected light radiates from the centre to the lower front edge

The cone of light on the tympanic membrane

A small, lax, triangular area at the top, without the fibrous middle layer, named after an English anatomist of the early nineteenth century

The pars flaccida — Shrapnell's membrane

Three layers: skin on the outside, radiating and circular fibres in the middle, mucous membrane on the inside

The tympanic membrane — cutaneous, fibrous and mucosal layers

Sensory supply shared by three different cranial nerves: the trigeminal, the glossopharyngeal and the vagus

The tympanic membrane, supplied by the auriculotemporal, tympanic (Jacobson's) and auricular (Arnold's) nerves

A tiny incision followed by insertion of a small tube called a grommet, to drain a sticky effusion in a child

Myringotomy with grommets — treating glue ear by ventilating through this membrane

Ruptured by a sudden blast, a slap to the ear or a cotton bud, usually healing itself within weeks

Perforation of the tympanic membrane

Key ideas

The drum is about seventeen times larger in effective area than the oval window, and this ratio plus the lever action of the ossicles is what lets airborne sound drive the fluid of the inner ear.
Because the drum is skin on one side and mucosa on the other, it is unusually thin, and skin cells from the outer surface migrate outwards like a conveyor belt to keep it clean.

Quick-fire facts

•About 9–10 mm in diameter, 0.1 mm thick, and tilted so that its upper edge lies more lateral than its lower edge
•The tympanic annulus is the fibrocartilaginous ring in which the membrane is held in a groove of the temporal bone
•The chorda tympani, a branch of the facial nerve carrying taste from the front of the tongue, crosses the inner surface of the drum
•The pars tensa forms most of the membrane; the pars flaccida (Shrapnell's membrane) is a small area above the lateral process of the malleus
•Named from the Greek tympanon, 'drum'; the Latin term is membrana tympanica and 'myringa' is an alternative name
•Retraction pockets in the pars flaccida can form cholesteatoma, an expanding sac of skin debris in the middle ear
•A perforation causes a conductive hearing loss of up to about 40 dB depending on size
•Glue ear (otitis media with effusion) is very common in preschool children, and grommets are one of the commonest operations in UK children

Drill it — 7 cards

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Sources

Kenhub — Tympanic membrane: anatomy, structure and function
NHS — Glue ear