Tympanic membrane

The tympanic membrane is a thin membrane that separates the external ear from the middle ear. It acts to transmit sound waves from air in the external auditory canal (EAC) to the ossicles of the middle ear.

Gross anatomy

The tympanic membrane is shaped like a flat cone pointing into the middle ear. The deepest point at the centre of the concavity is called the umbo. 

It consists of three layers (from external to internal):

1. Outer epithelial layer - consisting of stratified squamous epithelium continuous with the skin of the EAC ⁴

2. Middle fibrous layer (lamina propria) - consisting of fibroelastic connective tissue and contains blood vessels and nerves of the tympanic membrane ⁴

3. Inner epithelial layer - non-keratinised simple cuboidal epithelium continuous with mucosa of the middle ear ⁴

It attaches to a horseshoe-shaped incomplete bony ring along the wall of the EAC, the tympanic annulus. The incomplete nature of its attachment results in two distinct portions of the membrane:

• pars tensa: the larger tense portion of the membrane surrounded by the annulus, which extends from the anterior and posterior malleolar folds at the level of the lateral process of the malleus to the inferior edge of the membrane

• pars flaccida: the smaller flaccid portion of the membrane where the annulus is deficient at the notch of Rivinus. It is located above the anterior and posterior malleolar folds 

Quadrant separation

It is anatomically separated into four quadrants by drawing an in imaginary straight line continuing from the manubrium to the tympanic edge and another straight line at the umbo perpendicular to the first line ⁴. The four quadrants are:

• anterosuperior

• anteroinferior

• posteroinferior

• posterosuperior

This is important because vessels and nerves (specifically chorda tympani nerve) pass through the superior portion of the membrane. Additionally, the light reflex (cone of light) is specific to the anteroinferior portion of the membrane. Thus, when intervention is performed, the posteroinferior portion of the membrane is chosen.

Arterial supply

• external surface

  • deep auricular artery (branch of maxillary artery)

• internal surface

  • anterior tympanic artery (branch of maxillary artery) 

  • stylomastoid branch of posterior auricular artery (branch of external carotid artery)

Innervation

The membrane has two distinct nerve supplies based on the different embryological origins of the internal and external surfaces.

• external surface

  • predominantly the auriculotemporal nerve (CN V3)

  • greater auricular nerve (C2, C3)

  • some authors report some minor contribution from the auricular branch (Arnold's nerve) of the vagus nerve (CN X)

• internal surface: tympanic branch (Jacobson nerve) of the glossopharyngeal nerve (CN IX)

Related pathology

• conductive hearing loss: secondary to rupture or perforation

• tympanic membrane retraction

• tympanic membrane bulging

• myringosclerosis

See also

• tympanostomy tube insertion