Auditory Mechanics

 

The moustached bat Pteronotus Parnellii

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Finite-element model of the moustached bat

 

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Pteronotus parnellii
Moustached bat,
Brazil. Photo by L. H. Emmons.
Smithsonian Institution, 1997

The moustached bat (Pteronotus parnellii) can be distinguished by stiff hairs around its mouth, which give the appearance of a moustache. It has folds of skin on its lower lip, its chin is covered by wart-like bumps, and the colour of its fur is medium- to dark-brown. Its weight at maturity is approximately 10 to 14 grams and its wingspan is about 340 to 350 mm. It lives deep in the large inner chambers and passageways of caves, in colonies of approximately 5000 bats, and feeds upon insects.

The moustached bat belongs to the suborder Microchiroptera. This type of bat makes use of echolocation to find its way in darkness, to avoid obstacles and to capture insect prey. Echolocation involves the emission of ultrasonic pulses which may have intensities as high as 120 dB SPL. Subsequent to the emission the system detects low-intensity reflections bouncing from obstacles and insect prey. The bat is able to attenuate the loud outgoing sounds and then be in a highly sensitive state to perceive faint echoes within a matter of milliseconds.

The moustached bat middle ear is equipped with a set of very well developed muscles that contract and relax in synchrony with pulse emission and echo perception (Henson, 1970). The tensor tympani and stapedius muscle are striated muscles which attenuate sounds by tensing the tympanic membrane. In addition, an annular ring of radially oriented smooth muscle has recently been reported (Henson & Henson, 2000). This may provide a regulated state of tonic tension that affects the contraction and relaxation times of the striated (twitch) muscle. The smooth-muscle arrays described in the moustached bat have also been found in other species (Henson & Henson, 2001).

The annular ligament is a radially shaped ligament connecting the tympanic membrane to the tympanic ring. In mammals this ligament receives its blood supply through the numerous blood vessels which penetrate the ligament. It consists of radially arranged collagen fibres and numerous fibroblasts. In addition to the fibres and fibroblasts, Henson & Henson (2000) recently observed and reported the existence of a well-developed system of radially arranged smooth muscle cells. This system suggests the possibility of a tonic regulation of the tension of the tympanic membrane. The presence of smooth muscle fibres has also been confirmed for mice, gerbils, rats, and hedgehogs (Henson & Henson 2001). In humans, the fibres are present, though not as common, and in a more complicated branching arrangement (Henson 2000).

Annular ligament with clearly visible smooth muscle fibres.

 


Presentation about the finite-element model of the middle ear of the moustached bat. Presented as part of the BME Seminar Series on the 6th of December 2000.

 



References

Henson Jr. OW (1970): "The ear and audition"; in W.A. Wimstadt, "Biology of bats" Vol.2, Academic Press, 181-256

Henson Jr. OW, Henson MM (2000): "The tympanic membrane: highly developed smooth muscle arrays in the annulus fibrosus of mustached bats" JARO 1, 25-32

Henson MM, Rask-Andersen H, Madden VJ Henson OW (2001a): "The human tympanic membrane: Smooth muscle in the region of the annulus fibrosus" ARO MidWinter Meeting, St. Petersburg Beach. In press

Henson OW, Henson MM, Cannon J (2001b): "Comparative study of smooth muscle and collagen fibers in the attachment zone of the tympanic membrane" ARO MidWinter Meeting, St. Petersburg Beach. In press

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© Copyright Rene G. van Wijhe 2000 Contact: Rene G. van Wijhe