title: Structural analysis of the tongue and hyoid apparatus in a woodpecker.
abstract: Woodpeckers avoid brain injury while they peck at trees up to 20Hz with speeds up to 7m/s, undergoing decelerations up to 1200g. Along with the head, beak and neck, the hyoid apparatus (tongue bone and associated soft tissues) is subjected to these high impact forces. The shape of the hyoid apparatus is unusual in woodpeckers and its structure and mechanical properties have not been reported in detail. High-resolution X-ray micro-computed tomography and scanning electron microscopy with energy dispersive X-ray spectroscopy were performed and correlated with nanoindentation mapping. The hyoid apparatus has four distinct bone sections, with three joints between these sections. Nanoindentation results on cross-sectional regions of each bone reveal a previously unreported structure consisting of a stiff core and outer, more compliant shell with moduli of up to 27.4GPa and 8.5GPa, respectively. The bending resistance is low at the posterior section of the hyoid bones, indicating that this region has a high degree of flexibility to absorb impact. These new structural findings can be applied to further studies on the energy dissipation of the woodpecker during its drumming behavior, and may have implications for the design of engineered impact-absorbing structures.
  
  
  
  Woodpeckers avoid brain injury while they peck at trees, which results in extreme impact conditions. One common adaptation in woodpeckers is the unusual shape of the elongated tongue, also called the hyoid apparatus. The relationship between the structure and mechanical properties of the bony part of the hyoid apparatus has not been previously reported. A three dimensional model of the bony tongue was developed, and the hardness and stiffness were evaluated. A new type of bone structure, which is opposite of typical skeletal bone structure was found. The combined microstructural and mechanical property analysis indicate possible energy absorption routes for the hyoid apparatus and are applicable to the design of engineered structures.
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093, USA. Electronic address: jyjung@ucsd.edu.
authors.forename: Jae-Young
authors.initials: JY
authors.lastname: Jung
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Naleway
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, CA 92521, USA.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Yaraghi
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, CA 92521, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Herrera
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Vincent R
authors.initials: VR
authors.lastname: Sherman
authors.affiliation: National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Bushong
authors.affiliation: National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Ellisman
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, CA 92521, USA.
authors.forename: David
authors.initials: D
authors.lastname: Kisailus
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093, USA; Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Joanna
authors.initials: J
authors.lastname: McKittrick
mesh_terms: D000825:Animal Structures / Q000000981:diagnostic imaging*; D000818:Animals; D001717:Birds / Q000033:anatomy & histology* / Q000502:physiology; D006928:Hyoid Bone / Q000000981:diagnostic imaging*; D014059:Tongue; D055114:X-Ray Microtomography
keywords: Hyoid bone; Nanoindentation; Tongue; Woodpecker; X-ray micro-computed tomography