A new method for quantifying the complexity of muscle attachment sites

Skeletal muscles attach to bone at their origins and insertions, and the interface where tendon meets bone is termed the muscle attachment site (or enthesis). Muscle attachment sites function to anchor muscles/tendons to bone and to dissipate stress (force per unit area) resulting from force transmission. Mechanical stresses at the muscle/tendon‐bone interface are proportional to surface area of the bony attachment sites, so a larger muscle attachment site will distribute loads over a wider surface area. Muscles that are frequently active and/or are of larger size should cause muscle attachment sites to hypertrophy (training effect), so paleontological studies have often used characteristics of attachment sites as indicators of locomotor behavior.In studies of humans, muscle attachment sites have been used to infer physical activity of fossil specimens, with larger attachment sites assumed to indicate larger muscles and/or habitual use. For example, muscle attachment site morphology was examined in prehistoric Andean fishing and agricultural populations. From this data, anthropologists concluded that the fishing population had more muscular upper bodies while the agricultural population had more muscular lower bodies. Such differences in muscle attachment site morphology have been attributed to differences in physical activity levels and loading history of limb bones experienced by individuals during their lifetime. However, bone performance during loading is governed by both genetic factors and loading history, but also by age, sex, and epigenetic factors. Thus, controversy arises when paleontologists attempt to infer the past loading history (i.e., activity levels) of individuals from bone morphology.We studied 4 replicate lines of high runner (HR) mice that had been selectively bred for 57 generations based on the average number of wheel revolutions on days 5 & 6 of a 6‐day period of wheel access. Four additional lines have been bred without regard to wheel running and serve as controls (C). On average, mice from HR lines voluntarily run ~3 times more than C mice on a daily basis. We housed 100 mice with or without wheels for 12 weeks starting at weaning. We quantified the evolved differences in muscle attachment site morphology between HR and C mice as well as plastic changes resulting from chronic exposure to exercise by measuring the cortical cross‐sectional areas, linear dimensions, and total surface area for muscles that attach on the femur and humerus. Sites chosen for subsequent analysis included the femoral third trochanter, an insertion point for the quadratus femoris, and the humerus deltoid crest, an insertion point for the spinodeltoideus, superficial pectoralis, and acromiodeltoideus.With body mass as a covariate, HR mice had significantly larger humerus deltoid tuberosities than C, with no significant training effect. Morphology of the femoral third trochanter did not differ between HR and C mice and was unaffected by chronic wheel access. Our results suggest that muscle attachment site morphology is largely determined by genetic background rather than exercise during ontogeny.3D Model of the Femoral Third Trochanter of a MouseFigure 1

Development of the Indirect Flight Muscle Attachment Sites inDrosophila:Role of the PS Integrins and thestripeGene

Past research has indicated that the ethnic composition of residential neighbourhoods influences inter‐ethnic contact. However, little attention has been paid to individual activity and travel patterns which encompass encounters with others at physical and virtual activity sites, such as sports clubs and online chat rooms. By analysing a Dutch dataset on the life of urban ethnic minorities, we found that individual activity patterns are important factors in explaining inter‐ethnic contact. Activities such as sports, attending parties or religious gatherings, using Internet, and hosting friends and neighbours influence the extent of inter‐ethnic contact. The effect of ethnic composition of neighbourhoods and educational qualification on relative frequency of contact with native Dutch is strongly reduced when individual activity and travel patterns are taken into account. For receiving practical help from native Dutch, neighbourhood effects were insignificant.

Avulsion of muscles from the femoral trochanter in the fowl

This study presents a novel three-dimensional analysis using statistical atlases and automated measurements to assess diaphyseal morphology of the clavicle and its relationship to muscle asymmetry. A sample of 505 individuals (285 males, 220 females) from the William McCormick Clavicle Collection was CT scanned, segmented, and added to a statistical bone atlas that captures correspondence between homologous points on the bone surfaces. Muscle attachment sites were localized on the atlas and then propagated across the entire population. Cross-sectional contours were extracted at 5% increments along the entire bone, as well as at muscle attachment sites and the clavicle waist; maximum and minimum dimensions of each cross-sectional contour were calculated. In addition, the entire three-dimensional surface was examined for asymmetry by analyzing the magnitude and directional differences between homologous points across all bone surfaces in the dataset. The results confirm the existing studies on clavicle asymmetry, namely that the left clavicle is longer than the right, but the right is more robust than the left. However, the patterns of asymmetry are sexually dimorphic. Males are significantly asymmetric in all dimensions and at muscle and ligament attachment sites (P < 0.05), whereas female asymmetry is more variable. We hypothesize that this is related to absolute and relative differences in male muscle strength compared to females. However, an area with no muscle attachments on the posterior midshaft was significantly asymmetric in both sexes. We suggest that this is a curvature difference caused by opposing muscle actions at the medial and lateral ends of the bone.

Skeletal muscles attach to bone at their origins and insertions, and the interface where tendon meets bone is termed the attachment site or enthesis. Mechanical stresses at the muscle/tendon-bone interface are proportional to the surface area of the bony attachment sites, such that a larger attachment site will distribute loads over a wider area. Muscles that are frequently active and/or are of larger size should cause attachment sites to hypertrophy (training effect); however, experimental studies of animals subjected to exercise have provided mixed results. To enhance our ability to detect training effects (a type of phenotypic plasticity), we studied a mouse model in which 4 replicate lines of High Runner (HR) mice have been selectively bred for 57generations. Selection is based on the average number of wheel revolutions on days 5 & 6 of a 6-day period of wheel access as young adults (6-8weeks old). Four additional lines are bred without regard to running and serve as non-selected controls (C). On average, mice from HR lines voluntarily run ~3 times more than C mice on a daily basis. For this study, we housed 50 females (half HR, half C) with wheels (Active group) and 50 (half HR, half C) without wheels (Sedentary group) for 12weeks starting at weaning (~3weeks old). We tested for evolved differences in muscle attachment site surface area between HR and C mice, plastic changes resulting from chronic exercise, and their interaction. We used a precise, highly repeatable method for quantifying the three-dimensional (3D) surface area of four muscle attachment sites: the humerus deltoid tuberosity (the insertion point for the spinodeltoideus, superficial pectoralis, and acromiodeltoideus), the femoral third trochanter (the insertion point for the quadratus femoris), the femoral lesser trochanter (the insertion point for the iliacus muscle), and the femoral greater trochanter (insertion point for the middle gluteal muscles). In univariate analyses, with body mass as a covariate, mice in the Active group had significantly larger humerus deltoid tuberosities than Sedentary mice, with no significant difference between HR and C mice and no interaction between exercise treatment and linetype. These differences between Active and Sedentary mice were also apparent in the multivariate analyses. Surface areas of the femoral third trochanter, femoral lesser trochanter, and femoral greater trochanter were unaffected by either chronic wheel access or selective breeding. Our results, which used robust measurement protocols and relatively large sample sizes, demonstrate that muscle attachment site morphology can be (but is not always) affected by chronic exercise experienced during ontogeny. However, contrary to previous results for other aspects of long bone morphology, we did not find evidence for evolutionary coadaptation of muscle attachments with voluntary exercise behavior in the HR mice.

The morphology of muscle attachment sites, or entheses, has long been assumed to directly reflect in vivo muscle activity. The purpose of this study is to examine whether variations in muscle activity that are within normal physiological limits are reflected in variations in external attachment site morphology. This study tests the hypothesis that increased muscle activity (magnitude, number and frequency of loading cycles) results in the hypertrophy of muscle attachment sites. The attachment sites of six limb muscles and one muscle of mastication (control) in mature female sheep were measured and compared in exercised (weighted treadmill running for 1 h per day for 90 days) and sedentary control animals. Attachment site surface morphology was assessed by quantifying the size (3D surface area) and complexity (fractal dimension parallel and perpendicular to soft tissue attachment) of the surfaces. The results of this study demonstrate no effect of the exercise treatment used in this experiment on any measure of enthesis morphology. Potential explanations for the lack of exercise response include the mature age of the animals, inappropriate stimulus type for inducing morphological change, or failure to surpass a hypothetical threshold of load for inducing morphological change. However, further tests also demonstrate no relationship between muscle size and either attachment site size or complexity in sedentary control animals. The results of this study indicate that the attachment site morphological parameters measured in this study do not reflect muscle size or activity. In spite of decades of assumption otherwise, there appears to be no direct causal relationship between muscle size or activity and attachment site morphology, and reconstructions of behavior based on these features should be viewed with caution.

The degree of mineralization of bone (DMB) in the human mandibular condyle is heterogeneous, and differences in DMB have been related to variations in bone turnover caused by local strains. The lateral pterygoid muscle inserts at the anterior surface of the condyle. The aim of this study is to analyze the DMB at the attachment of this muscle as compared with a control region. It was hypothesized that, DMB at the attachment sites of lateral pterygoid muscles was lower than at the control regions, because of the larger number of loadings and subsequently higher remodeling rates. Also, as the human lateral pterygoid muscle is heterogeneous in its internal architecture, variations in DMB within the attachment sites were expected. 10 human mandibular condyles were scanned in a micro CT system. Within each condyle, two regions, that is, the pterygoid fovea and a posterior (control) region where no muscle was inserted, were selected to analyze regional differences in DMB. The attachment site was further divided into eight subregions to analyze subregional differences. At the pterygoid fovea the DMB of cortical bone was significantly lower than at the control region (p = 0.003) and increased in medio-lateral direction. The results of this study could suggest an influence of the lateral pterygoid muscle on bone turnover at this site.

Proximal femoral morphology and associated musculature are of special relevance to the understanding of hominoid locomotor systems. Knowledge of bone-muscle correspondence in extant hominoids forms an important comparative basis for inferring structure-function relationships in fossil hominids. However, there is still a lack of consensus on the correspondence between muscle attachment sites and surface morphology of the proximal femoral diaphysis in chimpanzees. Two alternative observations have been proposed regarding the attachment site positions of gluteus maximus (GM) and vastus lateralis (VL) relative to two prominent surface features of the proximal femoral diaphysis, the lateral spiral pilaster and the inferolateral fossa. Here, we use a combination of virtual and physical dissection in an attempt to identify the exact correspondence between muscle attachment sites and osteological features in two specimens of Pan troglodytes verus. The results show that the insertion of the GM tendon is consistently inferolateral to the lateral spiral pilaster, and that a part of the inferolateral fossa consistently forms the attachment site of the VL muscular fibers. While overall musculoskeletal features are similar in the two specimens examined in this study, GM and VL exhibit different degrees of segregation at the level of the inferolateral fossa. One specimen exhibited tendinous GM fibers penetrating the posteromedial part of VL, with both GM and VL inserting at the inferolateral fossa. In the other specimen, GM and VL were separated by a lateral intermuscular septum, which inserted into the inferolateral fossa. Variation of proximal femoral muscle attachments in chimpanzees is thus greater than previously thought. Our results indicate that a conspicuous osteological feature such as the inferolateral fossa does not necessarily correspond to the attachment site of a single muscle, but could serve as a boundary region between two muscles. Caution is thus warranted when interpreting the surface topography of muscle attachment sites and inferring locomotor functions.

Intertissue Mechanical Stress Affects Frizzled-Mediated Planar Cell Polarity in the Drosophila Notum Epidermis

In dinosaurs, as in other reptiles, the homologue of the mammalian zygomatic bone is the jugal. The dinosaurian jugal was primitively triradiate, with posterior, dorsal and anterior processes that respectively contacted the quadratojugal, the postorbital, and the maxilla and lacrimal. However, the jugal evolved along different lines in the three major dinosaurian clades. In theropods this cranial element remained relatively conservative in morphology, apart from being reduced to a rod-like structure in most birds and a few non-avians. In sauropodomorphs the jugal eventually became small, plate-like and nearly restricted to the area below the orbit, even being excluded from the ventral margin of the skull in many derived taxa. Among ornithischians the jugal was highly variable, but in many cases became large and/or adorned with ornamental features such as horns, flanges, and rugosities. The jugal does not appear to have been a site of muscle attachment in most non-avian dinosaurs, but represented an important structural element in the akinetic dinosaurian skull. The conspicuous jugal ornaments seen in many ornithischian dinosaurs, like the less striking ones documented in some saurischians, may have played an important role in the social behavior of the species that possessed them. In many cases they have a weapon-like aspect suggesting use in aggressive displays, if not actual combat, adding to the evidence that agonistic behavior was likely widespread among ornithischians in particular. Anat Rec, 300:30-48, 2017. © 2016 Wiley Periodicals, Inc.

Smilodon fatalis is the Rancho La Brea saber‐tooth cat with robust extremities and a short tail, and is believed to be an ambush predator. In this study, select pelvic, femoral, and tibial muscle attachment sites were determined for Smilodon fatalis based on osteological muscle scars and comparisons with muscle attachment site maps developed for Neofelis nebulosa (clouded leopard) and Felis catus (domesticated cat). Following careful dissection of several specimens of the cat and clouded leopard, the results showed that a comparison of the muscle attachment sites, proportional muscle weights, and muscle attachment site surface areas were remarkably similar. Comparison of Smilodon muscle scar locations and muscle scar surface areas with those of the cat and clouded leopard showed that all three species were also similar. Given these similarities, we are confident that our estimated recreation of the muscle attachment sites in Smilodon is reasonably accurate. In addition, we found that the attachment sites of the quadriceps femoris muscles in Smilodon had increased levels of rugosity compared to the clouded leopard and cat, supporting the concept that this animal may have been an ambush predator that required more robust muscles to leap at and grapple with prey.Grant Funding SourceNone

Owls have the largest head rotation capability amongst vertebrates. Anatomical knowledge of the cervical region is needed to understand the mechanics of these extreme head movements. While data on the morphology of the cervical vertebrae of the barn owl have been provided, this study is aimed to provide an extensive description of the muscle arrangement and the attachment sites of the muscles on the owl’s head-neck region. The major cervical muscles were identified by gross dissection of cadavers of the American barn owl (Tyto furcata pratincola), and their origin, courses, and insertion were traced. In the head-neck region nine superficial larger cervical muscles of the craniocervical, dorsal and ventral subsystems were selected for analysis, and the muscle attachment sites were illustrated in digital models of the skull and cervical vertebrae of the same species as well as visualised in a two-dimensional sketch. In addition, fibre orientation and lengths of the muscles and the nature (fleshy or tendinous) of the attachment sites were determined. Myological data from this study were combined with osteological data of the same species. This improved the anatomical description of the cervical region of this species. The myological description provided in this study is to our best knowledge the most detailed documentation of the cervical muscles in a strigiform species presented so far. Our results show useful information for researchers in the field of functional anatomy, biomechanical modelling and for evolutionary and comparative studies.

Basal tubulobulbar complexes (TBCs) that occur at attachment sites between neighboring Sertoli cells are subcellular machines that internalize intercellular junctions during movement of spermatocytes from basal to adluminal compartments of the seminiferous epithelium. Each complex consists of an elongate tubular extension of two attached plasma membranes, and is capped at its distal end by a clathrin-coated pit. The tubular region is surrounded by a cuff of actin arranged in a dendritic network. Near the end of the complex, a bulbous region forms that lacks the actin cuff but is closely associated with cisternae of endoplasmic reticulum. The bulb eventually buds from the complex and enters endocytic compartments of the Sertoli cell. Previous research has shown that when the actin network is perturbed using the actin filament-disruptor, cytochalasin D, apical tubulobulbar complexes that are associated with spermatids were associated with lower levels of actin, patchy actin networks and swollen tubular regions. Here we explored the effects of actin network perturbation on the morphology of basal tubulobulbar complexes in stage V seminiferous tubules. Isolated rat testes were perfused ex vivo for one hour with oxygenated Krebs-Henseleit buffer (with BSA) containing either 40 μM cytochalasin D or control solution containing DMSO and perfusion-fixed for electron microscopy. Compared to control, actin cuffs in drug-treated TBCs appeared less uniform and patchy. In addition, the tubular regions of the complexes appeared swollen. Our results are consistent with the conclusion that intact networks of actin filaments are required for maintaining the structural integrity of basal TBCs. Anat Rec, 299:1449-1455, 2016. © 2016 Wiley Periodicals, Inc.

Recent studies in our laboratory have developed maps of pelvic musculature attachment sites (muscle maps) for Neofelis nebulosa (clouded leopard), Felis catis (domestic cat) and &gt;Canis latrans (coyote). Correlations were made between actual muscle attachments and bone morphology at the attachment site. Based on this information we can map muscle attachment sites on bones from extinct closely related species. Pleistocene pelvis specimens were examined for bony muscle attachment sites, measured and photographed at the George C. Page Museum in Los Angeles, California. Specimens included Smilodon fatalis (n=9), Panthera atrox (n=4), Canis dirus (n=6), Canis latrans (n=5), and Arctodus simus (n=2). Muscle map surface areas for eight pelvic muscles were determined for each specimen along with pelvic measurements (ilium/ischium: width/length). The measurements were then compared between and within extant and extinct species listed above. Mm. gluteus medius, quadratus femoris, cranial and caudal gemellus surface areas differed significantly in comparisons between the felids, and between felids and non‐felid species in both extinct and extant groups. Pelvic measurements differed primarily between felid and non‐felids. These results suggest that muscle map surface area analysis may be useful for both phylogenetic and morphometric analysis.