Tympanum

Definition

A thin, membrane-covered auditory organ that detects sound vibrations in insects and some other arthropods; the functional equivalent of an eardrum. Tympana are typically located on the legs, thorax, or abdomen, and are coupled to internal chordotonal organs that transduce mechanical vibrations into neural signals. The term also applies to the external membrane itself (the tympanic membrane) and, by extension, to the entire hearing apparatus including associated air sacs and sensory structures.

Etymology

Latin, from Greek tympanon, meaning drum or drumhead

Example

In field crickets (Gryllidae), the tympana are located on the proximal tibiae of the forelegs, where two oval membranes face each other across a tracheal air chamber; this bilateral arrangement allows directional hearing by comparing arrival times and intensities of sound at the two ears.

Synonyms

• tympanal organ
• tympanic organ

Related Terms

• Chordotonal organ
• Johnston's organ
• subgenual organ
• tympanic nerve
• tympanic trachea
• tympanate
• atympanate

Usage Notes

The plural form tympana is standard in technical writing. Specialists distinguish the tympanum (the external membrane) from the tympanal organ (the complete hearing structure including the scolopidial sensilla beneath). Not all insects have tympana; some groups detect sound through substrate vibration or other non-tympanal mechanisms. The term is also used in vertebrate anatomy (frog tympanum, mammalian tympanic membrane) but the arthropod structure is convergent, not homologous. Contrast with atympanate: lacking a tympanal organ.