Crista acustica (also Siebold's organ, or crista acoustica) is a part of the hearing organ (tibial organ) in some insects (e.g. grasshoppers, crickets, katydids). It is a collection of sensory cells that form a crest (hence the name) on top of the hollow tube (the foreleg

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing animals with lungs. The trachea extends from the ...

) behind the hearing membrane (tympanum) on the legs of the insect. The crista acustica is a transition from the intermedia organ (from the midline to the periphery), together which compose the tibial hearing organ (as opposed to the tympanal hearing organ). The crista acustica is one of three fiddle-string-like organs or

chordotonal organ Chordotonal organs are stretch receptor organs found only in insects and crustaceans. They are located at most joints and are made up of clusters of scolopidia that either directly or indirectly connect two joints and sense their movements relati ...

in insects: the others are the intermediate organ and the supratympanal organ/

subgenual organ The subgenual organ is an organ in insects that is involved in the perception of sound. The name (Latin ''sub: "''below" and ''genus: "''knee") refers to the location of the organ just below the knee in the tibia of all legs in most insects. The f ...

. These chordotonal organs are actually collections of sensory cells sensitive to vibration (these cells are called scolopidia cells). Their cells are attached to the tube in the legs of the insects (the trachea, "''trah-key-ah''"). So when the tube vibrates, the cells vibrate. In the crista acustica, it turns out that different scolopidia cells are sensitive to different vibrations depending on the frequency of the vibration. Since these organs are sensitive to vibrations (due to changes in pressure.cf. far field pressure gradients, as opposed to pure displacement sensations or near field acoustics It turns out the cells closest to midline are the largest and sensitive to the lowest frequency (low frequencies having the largest wavelength), and the cells further out (distal) are smaller and sensitive to higher frequencies (since high frequencies have shorter wavelengths). This orderly arrangement of sensory cells gives the insect the ability to discriminate frequencies, much like the inner ear of mammals.

References

Sensory organs in animals Insect anatomy Auditory system {{insect-anatomy-stub

See also

References