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How does the eardrum respond when sound waves reach it?

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Diagram showing auditory mechanisms in insects, including labeled illustrations of a scolophore organ, the mosquito ear with antenna shaft and scolophores, the cicada ear with auditory capsule and tympanic membrane, and the grasshopper ear with sensory body and tympanic membrane. — sound reception Auditory mechanisms in insects. (Left) A scolophore organ. (Top right) The mosquito ear. (Centre right) The ear of the cicada *Magicicada septendecim*. (Bottom right) The ear of the grasshopper.

When sound waves reach the tympanic membrane (eardrum), a portion of the sound is reflected, while the absorbed energy sets the membrane into motion. The membrane acts as a stiff cone, vibrating inward and outward in response to the sound waves.1

The physical characteristics of this response are directly related to the sound's properties:
* Loudness: Greater force from sound waves results in increased deflection of the membrane.1
* Pitch: Higher frequency sounds cause the membrane to vibrate more rapidly.1

The central portion of the membrane, known as the umbo, is attached to the handle of the malleus. As the eardrum vibrates, it transfers this motion to the ossicular chain, which acts as an impedance-matching transformer to transmit vibrations into the fluids of the inner ear. Additionally, the tension of the membrane can be modulated by the tensor tympani muscle, which pulls the malleus inward to adjust the intensity of the sound.123