Middle ear anatomy

Middle Ear Anatomy

Move the cursor over the graphic to identify structures

The middle ear (ME) and contents serve to transmit external sound energy to the components of the inner ear. Sound pressure applied to the ear drum (tympanum) creates motion which is transmitted through the ossicles to the oval window. The oval window membrane is the interface with the inner ear. The inner ear is where motion is translated to neural signals.

The ME is a cavity which lies at the end of the eustachian tube

The eustachian tube passes from the nasopharynx through the temporal bone to the ME

The tube is composed of membrane and cartilage

A continuous membrane from the nasopharynx to the mastoid lines, nourishes and protects all structures within the middle ear.

The cellular composition of this membrane gradually changes from:
- ciliated cells of the nasopharynx to tall columnar, interspersed with goblet, cells in the middle ear space to,
- cuboidal cells in the mastoid.
The continuity of this membrane provides an unbroken pathway for the transmission of pathogens from the nasopharynx to the mastoid sinus.
Ventilation via the eustachian tube is central ME health. To work properly, the eustachian tube must be able to open and close. Click "open" and "close" on the graphic above, and observe the activity of the dilator tubae muscle as the lumen of the tube opens and closes.

At rest, the eustachian tube is collapsed closed. During the acts of swallowing or yawning, air is allowed to enter the lumen through an orifice within the nasopharynx

The tube opens by contraction of the dilator tubae muscle. The dilator tubae is the medial bundle of the tensor veli palantini muscle.

Any condition which affects the function of the dilator tubae will affect the patient's ability to aerate and drain the ME. Conditions which can limit efficient contraction of the dilator tubae muscles include:

craniofacial defects such as cleft palate, trisomy 21, etc.
craniofacial trauma,
neuromuscular defects,
tumors, etc.

Eustachian tube function is also affected by the physical development of the child. As children mature from infants to toddlers, and then into childhood, a number of anatomical and physiologic changes occur which reduce the frequency of OM. Among these changes are:
- Development of muscular structures attached to the eustachian tube help maintain patency when the dilator tubae contract.
- Development and stiffening of cartilaginous elements of the tube help maintain patency when the dilator tubae contract.
- Increases in both the length and angle of the tube work to limit fluid entering the ME.
- Maturation of the immune system increases resistance to pathologic organisms.

Instant Feedback:

The dilator tubae contracts to close the opening of the eustachian tube.