trumhinna

The trumhinna, or tympanic membrane, is a thin, semitransparent membrane that separates the external auditory canal from the middle ear. It is roughly 9 millimeters in diameter and is concave, with a central depression called the umbo where the handle of the malleus attaches.

Structure and appearance: The tympanic membrane consists of three layers: an outer epithelial layer continuous with the skin of the external auditory canal, a middle fibrous layer with radial and circular collagen fibers that provide strength, and an inner mucous membrane continuous with the mucosa of the middle ear. On otoscopy, the outer surface commonly displays a cone of light in the anteroinferior quadrant.

Function: The membrane vibrates in response to sound and transmits mechanical energy to the auditory ossicles (malleus, incus, stapes), facilitating the conversion of airborne sound into fluid-mediated vibrations in the inner ear. It also contributes to impedance matching and helps protect the middle ear from excessive pressure changes.

Innervation and blood supply: The outer surface is primarily supplied by the auriculotemporal nerve, with minor contributions from the auricular branch of the vagus nerve. The inner surface is innervated by the tympanic branches of the glossopharyngeal nerve. Blood supply comes from branches of the external carotid system, including the deep auricular artery.

Clinical notes: Perforation of the tympanic membrane can result from trauma or infection and may heal spontaneously or require tympanoplasty if persistent. Inflammation of the middle ear (otitis media) can cause bulging or retraction of the membrane. The membrane’s appearance as a pearly gray, translucent structure helps guide diagnosis during ear examinations.