Correspondence to: Ellen C. Jensen, 35 Southern Cross Road, Kohimarama Auckland 1071, New Zealand. E-mail: email@example.com
Shearing Mechanics and the Influence of a Flexible Symphysis During Oral Food Processing in Sphenodon (Lepidosauria: Rhynchocephalia) by Marc E.H. Jones, Paul O'Higgins, Michael J. Fagan, Susan E. Evans, Neil Curtis. Anat Rec 295:1075–1091.
Oral food processing involves food being changed by contact with parts of the mouth, including the jaws, tongue, palate, and teeth. Most lepidosaurs (snakes, lizards, and tuatara) at least partially process food orally. In particular, Sphenodon (New Zealand tuatara), has a specialized unique feeding action among amniotes where the lower jaw closes between two upper rows of teeth, which then slide forward tearing food apart. This shearing process of feeding is comparable with the powerful chewing stroke of mammals. However, there is controversy on the sophistication of the shearing mechanism in the tuatara. Because the tuatara is rare and a protected species, invasive work on living animals is restricted. Therefore, the authors investigated detailed jaw movement of the tuatara using skeletal material and the computer modeling approach of multibody dynamics analysis. This enables examination of the three-dimensional geometry of muscle forces, feeding structures, and contact forces. The authors show that flexibility at the mandibular symphysis is necessary for shearing to occur and this enables the jaws to move backwards when the jaw opens and forwards after the jaw closes. The authors' findings demonstrate that complex oral food processing occurs in some ectothermic amniotes. While the type of feeding by the tuatara is unique among amniotes today, the fossil record indicates that this type of feeding was more commonly found in the Mesozoic period. This might have been an advantage with unpredictable food availability, which might also currently be the case.
Shape Analysis of the Corpus Collosum and Cerebellum in Female MS Patients with Different Clinical Phenotypes by Deniz Sigirli, Ilker Ercan, Senem Turam Ozdemir, Ozlem Taskapilioglu, Bahattin Hakyemez, Omer Faruk Turan. Anat Rec 295:1202–1211.
Multiple sclerosis (MS) is a disabling disease of the central nervous system. A feature of MS is brain atrophy, which affects both gray and white matter. The corpus callosum is the largest white matter structure in the human brain and is involved in transfer of information between hemispheres. The corpus callosum is often damaged over the course of MS. Additionally, the cerebellum is a major site where the myelin sheath of neurons becomes damaged in MS. The authors investigated the differences in the shape of the corpus callosum and cerebellum of female relapsing-remitting MS and secondary progressive MS patients compared with healthy persons. Magnetic resonance imaging (MRI) scans were performed. Statistical shape analysis, which compares body forms, using particular landmarks obtained by anatomical prominences, was performed using the MRI scans. Landmarks were chosen based on cerebellar morphological descriptions, maximizing anatomical coverage, and reliability. The authors show that deformation of the shape of the corpus callosum and cerebellum is present in both types of MS patients. Their findings suggest that a land-marked based geometrical morphometric method is useful for determining shape differences in the corpus callosum and cerebellum in MS patients. These study results can serve as a reference for clinical studies in the future.
Human Masseter Muscle Fibers from the Elderly Express Less Neonatal Myosin Than Those of Young Adults by Erika Cvetko, Petř Karen, Jiří Janáček, Lucie Kubínová, Ana López Plasencia, Ida Eržen. Anat Rec 295:1364–1372.
The masseter muscle (in the jaw) is used for a variety of actions, including speech, mastication, swallowing, and jaw posture. This diversity of functions requires specific combinations of muscle compartments to stabilize the mandible during these tasks. In limb muscles, neonatal myosin (MyHC-neo) is only present just after birth, but jaw muscles contain a substantial amount of MyHC-neo in adults. There are no quantitative data on co-expression of MyHC-neo and adult myosin heavy chain (MyHC) isoforms. Therefore, the authors determined the co-expression of adult MyHC isoforms with MyHC-neo in young, middle-aged, and elderly subjects to better understand aging muscle. They collected specimens from the anterior superficial part of the masseter muscle in which the greatest changes in MyHC expression occur compared with the posterior part of masseter muscle. These specimens were stereologically analyzed for the amount of area of fibers expressing myHC isoforms and MyHC-neo. The complex morphology of the masseter muscle made it difficult to successfully analyze all samples. The authors found a reduction in the area of fibers that express MyHC-1 in elderly subjects compared with young subjects. They also found a decreased proportion of fibers with MyHC-neo in elderly subjects. This reduced amount of MyHC-neo with age suggests a lower ability for regeneration of the masseter muscle in elderly people. However, the precise role of MyHC-neo in this muscle still needs to be determined.
Ellen C. Jensen*
The Anatomical Record