Middle ear

Dr Dan J Bell and A.Prof Frank Gaillard et al.

The middle ear (a.k.a. tympanic cavity or tympanum) is an air-filled chamber in the petrous part of the temporal bone. It is separated from the external ear by the tympanic membrane, and from the inner ear by the medial wall of the tympanic cavity. It contains the three auditory ossicles whose purpose is to transmit sound vibrations from the tympanic membrane to the lateral wall of the inner ear

The tympanic cavity is further subdivided into three parts: the mesotympanum (the space directly medial to the tympanic membrane), superiorly the epitympanum or attic (the space superior to the membrane), and inferiorly, the hypotympanum, a shallow trough below the level of the membrane, from which the Eustachian tube arises 4. Some texts divide the middle ear into two compartments only: the tympanic cavity proper and the epitympanic recess.

The middle ear is shaped like a narrow box with concave sides. It has six walls:

1. The tegmental wall (roof): Formed by the tegmen tympani, a thin plate of petrous bone that also roofs in the canal for the tensor tympani and the tympanic antrum. It separates the dura mater on the floor of the middle cranial fossa from the tympanic cavity.

2. The jugular wall (floor): Formed by a thin layer of bone that separates the tympanic cavity from the superior bulb of the internal jugular vein.

3. The membranous (lateral) wall: This is formed entirely by the peaked convexity of the tympanic membrane and superiorly by the lateral bony wall of the epitympanic recess.

4. The labyrinthine (medial) wall: This separates the tympanic cavity from the inner ear. The initial part (basal turn) of the cochlea forms the promontory of the labyrinthine wall. It also features the oval and round windows, which communicate with the inner ear.

5. The mastoid (posterior) wall: This features the aditus (opening) to the mastoid antrum in its superior part, which connects the tympanic cavity to the mastoid cells. The canal for the facial nerve descends between the posterior wall and the antrum, medial to the aditus. Above this canal is the convex bulge of the lateral semicircular canal. Below the aditus there is a projection of a hollow cone, called the pyramid, which is perforated by the tendon of the stapedius.

6. The carotid (anterior) wall: This separates the tympanic membrane from the carotid canal. In its superior aspect there is an opening of the Eustachian tube (also known as the pharyngotympanic tube) and the canal for the tensor tympani.

Middle ear ossicles consist of three small bones (the malleus, incus and stapes), which form a mobile chain across the tympanic cavity from the tympanic membrane to the oval window.

There are two muscles, one for the malleus and one for the stapes, which act to damp down over-vibration from low-pitched sound waves. These are, respectively:

The chorda tympani leaves the facial nerve in the facial canal and enters the tympanic cavity through the posterior wall, lateral to the pyramid, lying just underneath the mucous membrane. It runs over the pars flaccida of the tympanic membrane, and the neck of the malleus. It leaves at the anterior margin of the tympanic notch.

Lymphatic drainage is to the parotid, retropharyngeal and upper deep cervical nodes.

This is by the tympanic branch of the glossopharyngeal nerve (Jacobson nerve), which forms the tympanic plexus by combining with sympathetic fibres from the internal carotid nerve. Branches from the plexus supply sensory and vasomotor fibres to the mucous membrane of the tympanic cavity, as well as to the tympanic membrane and external auditory meatus.

The middle and external ear are also supplied by branches of the trigeminal, facial, glossopharyngeal and vagus nerves which results in referred pain in the ear from other areas supplied by these nerves, e.g. the teeth, posterior part of the tongue, pharynx and larynx.

The tympanic plexus gives off the lesser petrosal nerve, which supplies the parotid gland via the otic ganglion.

Tympanum is derived from, tympanon (τύμπανον) the Greek word for drum.

Head and neck anatomy
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Article information

rID: 5574
System: Head & Neck
Section: Anatomy
Synonyms or Alternate Spellings:
  • Tympanic cavity
  • Middle ear cleft
  • Tympanum

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Cases and figures

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    Figure 1: middle ear anatomy (CT)
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    Figure 2: anatomy
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