@article{Biomechanics:1688,
      recid = {1688},
      author = {Orsbon, Courtney Peterson},
      title = {Swallowing Biomechanics of the Macaca mulatta Hyolingual  Apparatus},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2018-06},
      pages = {311},
      abstract = {Swallowing is essential to vertebrate life, yet its  biomechanical basis is poorly understood compared to other  behaviors such as chewing, suction feeding, reaching, and  locomotion. Human swallowing biomechanics is of clinical  interest for treating dysphagia, or difficulty swallowing,  with neuromuscular rehabilitation. Swallowing is also of  anthropological interest because purported adaptations for  speech also allow food and air to mingle near an open  larynx, which some argue renders humans maladapted to  swallowing. However, this hypothesis has not been  thoroughly tested and in fact is refuted by several studies  of human feeding physiology. This dissertation uses a  macaque (Macaca mulatta) model system to determine the  biomechanical basis of two important movements involved in  bolus propulsion and airway protection—tongue base  retraction and hyoid superoanterior excursion—and examines  how changes in hyolingual and craniofacial morphology over  the course of human evolution and ontogeny affect  hyolingual biomechanics. Tongue base retraction was caused  by neither extrinsic lingual muscle shortening nor  hydrostatic deformation. Kinematic evidence suggests that  suprahyoid muscles cause tongue base retraction by  regionally changing tongue volume, which is consistent with  a hydraulic linkage between the suprahyoid muscles and the  tongue.  These suprahyoid muscles are not only active and  shortening during tongue base retraction, but they also  rotate as they move the hyoid. This rotation either  amplifies or reduces hyoid velocity depending on the  geometry of the muscle and the direction of rotation. In  this way, suprahyoid muscles are functionally analogous to  pennate muscles, which also exhibit fiber rotation and  gearing. A computational model of hyoid range of motion  demonstrates that hyoid descent—which is commonly assumed  to be detrimental to swallowing—may actually help to  maintain swallowing performance as the human face has  shortened in recent evolutionary history, especially if  tongue volume must be preserved to maintain a hydraulic  linkage between the tongue and hyoid. Moreover, because  mandibular morphology affects suprahyoid muscle length,  selective pressure to maintain swallowing performance may  have resulted in the emergence of humanity’s characteristic  vertical mandibular symphysis and then chin. However,  geometric constraints require human suprahyoid muscles to  shorten relatively more when the hyoid is descended, which  may leave humans vulnerable to dysphagia not because the  human airway allows for more mixing of food and air near  the larynx but rather because of fundamental constraints on  vertebrate skeletal muscle biomechanics. Given that muscles  from the cranium, mandible, pharynx, soft palate, larynx,  sternum, and scapula all converge on this nexus of the  neck, the mammalian hyolingual apparatus may have an  underappreciated role in shaping the structures from which  it is so elegantly suspended.},
      url = {http://knowledge.uchicago.edu/record/1688},
      doi = {https://doi.org/10.6082/uchicago.1688},
}