Thin (~0.1 mm), semitransparent partition between external acoustic meatus and middle ear. Transmits sound vibrations to ossicles.

Position, Size, Orientation

Infants: bony EAM not developed; TM faces almost directly downwards → pull auricle downwards and backwards (not upwards/backwards/laterally as in adults)

Layers (Lateral → Medial)

Parts

Pars tensa — greater (lower) part; periphery thickened into fibrocartilaginous annulus tympanicus (fits tympanic sulcus); handle of malleus firmly embedded → pulls centre inward → umbo (point of maximum concavity)

Pars flaccida (Shrapnell’s membrane) — small triangular area superiorly, between anterior + posterior malleolar folds, above lateral process of malleus; thin/lax (fibrous layer replaced by loose areolar tissue); pinkish

Surfaces

Lateral (external): Concave; handle of malleus attached → umbo

Medial (internal): Convex; chorda tympani nerve crosses inner surface — runs forward in upper part, between fibrous + mucosal layers, lateral to long process of incus, medial to neck of malleus

Blood Supply

• Outer venous drainage → external jugular vein
• Inner venous drainage → transverse sinus + pterygoid venous plexus
• Lymphatics → preauricular + retropharyngeal nodes

Nerve Supply

Development

• From 1st pharyngeal membrane (3 layers):
  • Outer = ectoderm; middle = mesoderm; inner = endoderm

Analogous to the 3 layers of the trilaminar embryonic disc

Applied Anatomy

Clinical quadrants — 4 quadrants by 2 imaginary lines through umbo (one along malleus handle, one perpendicular); anterosuperior, anteroinferior, posterosuperior, posteroinferior

Otoscopic appearance — pearly grey; cone of light (light reflex) radiates from umbo in anteroinferior quadrant (~5 o’clock in right ear)

• Visible through membrane: handle of malleus (yellow streak, umbo upwards/forwards), lateral process of malleus (white prominence at upper end), long process of incus (white streak, behind + parallel to upper malleus handle)

Myringotomy — incision to drain middle ear pus; made in posteroinferior quadrant — avoids chorda tympani (runs across inner surface superiorly) and ossicles

Perforation — trauma or otitis media; pars flaccida perforations more serious (cholesteatoma risk)

Arnold’s reflex (referred cough) — irritation of auricular branch of vagus (CN X) in posterosuperior quadrant (ear wax, syringing, foreign body) → persistent cough or vasovagal syncope

The tympanic membrane (eardrum) is a thin (approximately 0.1 mm thick), semitransparent partition between the external acoustic meatus and the middle ear. It transmits sound vibrations from the external acoustic meatus to the ossicles of the middle ear.

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Position, Size, and Orientation

In infants, the bony external acoustic meatus is not yet developed; the tympanic membrane faces almost directly downwards. Hence, to examine the membrane in infants, the auricle is pulled downwards and backwards (not upwards, backwards, and laterally as in adults).

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Structure (Layers)

Three layers, from lateral to medial:

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Parts

Pars Tensa

Forms the greater (lower) part of the tympanic membrane. Its periphery is thickened into a fibrocartilaginous ring — the annulus tympanicus — which fits into the tympanic sulcus of the temporal bone. The handle of the malleus is firmly embedded in the fibrous layer of the pars tensa; its attachment pulls the membrane inwards at its centre, producing the umbo (point of maximum concavity).

Pars Flaccida (Shrapnell’s Membrane)

Small triangular area in the superior part of the membrane, between the anterior and posterior malleolar folds, above the lateral process of the malleus. It is thin and lax because the intermediate fibrous layer is replaced by loose areolar tissue. It appears slightly pinkish.

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Surfaces

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Blood Supply

Venous drainage:

• Outer surface → external jugular vein
• Inner surface → transverse sinus and pterygoid venous plexus

Lymphatic drainage: Preauricular and retropharyngeal lymph nodes.

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Nerve Supply

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Development

The tympanic membrane develops from the first pharyngeal membrane, which consists of three layers:

The three layers of the tympanic membrane are analogous to the three layers of the trilaminar embryonic disc.

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Applied Anatomy

Clinical Quadrants

The tympanic membrane is clinically divided into four quadrants by two imaginary lines crossing at the umbo:

• One line drawn along the handle of the malleus
• A second line perpendicular to it through the umbo

This gives: anterosuperior, anteroinferior, posterosuperior, and posteroinferior quadrants.

Examination with Otoscope

On illumination with an otoscope, the normal tympanic membrane appears pearly grey. The concavity produces a cone of light (light reflex) radiating from the umbo in the anteroinferior quadrant (at ~5 o’clock position in the right ear). The following structures are visible through the semitransparent membrane:

• Handle of malleus — yellow streak from the umbo upwards and forwards
• Lateral process of malleus — white prominence at the upper end of the streak
• Long process of incus — white streak behind and parallel to the upper handle of malleus

Myringotomy

Surgical incision of the tympanic membrane to drain pus from the middle ear. The incision is made in the posteroinferior quadrant — this avoids the chorda tympani nerve, which runs across the inner surface in the superior part, and avoids injuring the ossicles.

Perforation of the Tympanic Membrane

May result from external trauma, or from middle ear infection (otitis media). Perforations in the pars flaccida are more serious (cholesteatoma risk) than those in the pars tensa.

Referred Cough (Arnold’s Reflex)

Irritation of the auricular branch of the vagus (CN X — Arnold’s nerve) in the posterosuperior quadrant by ear wax, syringing, insects, or foreign bodies may reflexly cause a persistent cough (ear cough) or even vasovagal syncope.

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