Meeting Abstract

P2.106  Sunday, Jan. 5 15:30  Morphology and mechanical properties of the alligator larynx RIEDE, T*; LI, Z; TOKUDA, I; FARMER, C; University of Utah t.riede@utah.edu

Crocodilians have complex vocal communication. The production of sound requires the integration of respiratory and laryngeal functions. The alligator larynx appears to be a primitive vocal organ anatomically and it is not understood how this simple organ can produce such complex sounds. The ability of alligators to vary fundamental frequency is limited to variation in lung pressures and abduction and adduction of the vocal folds, but no stretching mechanism has been identified. In order to elucidate the mechanisms underpinning active vocal fold movement and passive vocal fold oscillations, computed tomography, histology and tensile tests were used to study the larynx. We found that while the abducting mechanism is facilitated by a single, comparatively large, uniform musculus cricoarytenoideus, adduction is facilitated by a more complex multi-belly muscle. Histological sections combined with differential staining were used to identify collagen, elastin, and hyaluronan in the vocal folds. Vocal fold connective tissue is highly organized, consisting of fibrillar proteins in a superficial layer as well as high amounts of hyaluronan, and randomly oriented collagen fibers in a deep layer. The alligator shares the layered vocal fold morphology with those of mammals. The design of vocal fold connective tissue represents an important feature affecting biomechanical properties. Tensile tests demonstrated a linear stress–strain response in the low-strain region and a nonlinear relationship in the high-strain region. These results suggest that alligator vocal folds are initially much stiffer than any mammalian vocal fold tested so far, but stress relaxation is also higher than in mammalian vocal folds. Refined computational modeling indicates that fundamental frequency, an important acoustic feature of alligator calls, can be reasonably well predicted using mechanical properties and a simple string model of tissue oscillation.