Human skeleton

Summary

The human skeleton is the internal framework of the human body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton makes up about 14% of the total body weight (ca. 10–11 kg for an average person) and reaches maximum mass between the ages of 25 and 30. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs. The human skeleton performs six major functions: support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation. The human skeleton is not as sexually dimorphic as that of many other primate species, but subtle differences

Official source

https://en.wikipedia.org/wiki/Human_skeleton

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While movement is essential to human wellbeing, we are still unable to reproduce the deftness and robustness of human movement in automatons or completely restore function to individuals with many types of motor impairment. To better understand how the human nervous system plans and controls movements, neuromechanists employ simple tasks such as upper extremity reaches and isometric force tasks. However, these simple tasks rarely consider impacts and may not capture aspects of motor control that arise from real-world complexity. Here we compared existing models of motor control with the results of a periodic targeted impact task extended from Bernstein's seminal work: hammering a nail into wood. We recorded impact forces and kinematics from 10 subjects hammering at different frequencies and with hammers with different physical properties (mass and face area). We found few statistical differences in most measures between different types of hammer, demonstrating human robustness to minor changes in dynamics. Because human motor control is thought to obey optimality principles, we also developed a feedforward optimal simulation with a neuromechanically inspired cost function that reproduces the experimental data. However, Fitts' Law, which relates movement time to distance traveled and target size, did not match our experimental data. We therefore propose a new model in which the distance moved is a logarithmic function of the time to move that yields better results (R-2 >= 0.99 compared to R-2 >= 0.88). These results support the argument that humans control movement in an optimal way, but suggest that Fitts' Law may not generalize to periodic impact tasks.

Frontiers Research Foundation2017

The Charter of Elements

Isabella Maria Pasqualini, Matthew Skjonsberg

An overview of the ‘new’ Charter of Athens, asserting and formulating the rights of the elements so as to ensure the fundamental right to life of all, from urban centers to the web of life upon which they rely – thereby fundamentally ‘advocating’ and ‘facilitating the use and development’ of human structures (both infrastructural and social) towards the resolution of all human-related crises: economical, social and environmental. A collection of essays addressing the proposed rights of water, earth, air and fire are assembled, proving the remarkable durability of intercultural, historic narratives of ‘the elements’ by demonstrating their relevance to contemporary questions of urbanization in a post-oil world.

2015

Intrinsic viscoelasticity increases temperature in knee cartilage under physiological loading

Philippe Abdel-Sayed, Mohamadreza Nassajian Moghadam, Dominique Pioletti

Metabolism of proteoglycans and hyaluronic acid has been shown to be temperature- dependent in cartilage explants, with optimal anabolic effects between 36 1C and 38 1C. At rest, the temperature of human knee has a value of around 33 1C. We aim to show in this study that viscoelastic properties of healthy human cartilage allow its temperature to reach those optimal temperatures during physiological mechanical loadings. We devel- oped a model allowing to determine the temperature increase in cartilage due to viscous dissipation. The model had three parameters, which were determined experimentally. The first parameter was the energy dissipated by cartilage samples submitted to cyclic stimulation. It was obtained with standard in vitro mechanical testing. The second parameter was the cartilage heat capacity and was measured in vitro with differential scanning calorimetry. Finally, the third parameter was the time constant of cartilage heat transfer and was obtained with in vivo magnetic resonance thermometry performed on four volunteers. With these experimentally determined parameters, the model predicted that cartilage dissipation is sufficient to raise the temperature in healthy knee cartilage from 33 1C to 36.7 1C after a 1 h walking. These results showed that intrinsic viscoelastic properties of the cartilage could induce a temperature increase optimal for the production of proteoglycans and hyaluronic acid. Interestingly, degenerated cartilage did not present high enough viscoelastic properties to significantly induce a temperature increase. Taken together, these data suggest an association between cartilage dissipation and its home- ostasis.

Elsevier2014