Development of Bipedal and Quadrupedal Locomotion in Humans--论文代写范文精选

四只脚的神经控制和双足运动过程，在猴子身上可能也适用于人类早期运动。第一个历史证据的步态分析，是亚里士多德(公元前384 - 322年),提出了第一个参考步态分析。然而他无法测试他的假设实验。下面的essay代写范文进行详述。

Introduction 
Locomotion is the movement of an organism from one place to another, often by the action of appendages such as flagella, limbs, or wings. In some animals, such as fish, locomotion results from a wavelike series of muscle contractions (The American Heritage® Science Dictionary, 2005). Walking is the act of traveling by foot; gait is the manner of walking; running is the act of traveling on foot at a fast pace; crawling is a slow mode of hand-knee or hand-foot locomotion. Quadrupedal locomotion, walking on all four extremities, is the most remarkable trait of the quadruped animals, and has been elegantly elaborated by dynamic selection processes over millions of years. Non-primate mammals usually utilize lateralsequence quadrupedalism, in which the hindlimb footfall leads the ipsilateral forelimb, whereas the non-human primates utilize a diagonal-sequence quadrupedalism, in which the hindlimb moves with the contralateral forelimb in a diagonal couplet. The neural control for the quadrupedal and bipedal locomotor processes in monkeys may also be applicable to human locomotion (Xiang, 2007).

Historical development 
The first historical evidence of the gait analysis is from the time of Aristotle (384-322 BC), who presented the first written reference to gait analysis (Baker, 2007). However, he was not able to test his hypothesis by experiment, and his observation-based ideas were later not supported by applying them to scientific experiments. Galileo Galilei (1564-1642) was the first to be able to test hypotheses by experiments, to prove any conjecture. Giovanni Alfonso Borelli (1608-1679), one of the Galileo’s pupils, first experimented to develop a gait analysis (Borelli, 1989). A rather detailed history of gait analysis was presented by Baker (2007). The first known instance of human quadrupedalism was reported by the great English photographer Eadweard Muybridge (1830-1904), who created movement by displaying individual photographs in rapid succession (Muybridge, 1901). The child with a paralyzed leg due to infantile poliomyelitis was photographed and animated by Muybridge (1887, 1901). Despite the paralyzed leg, the child was able to move using diagonal-sequence quadrupedal locomotion (Fig. 1).

The first description of human quadrupedalism in adults was that of Childs (1917), a British traveler, during his trip along the historical Baghdad Road, through Havza (Greek: Hafsa) near Samsun (Greek: Samsounta), in the middle region of the Black Sea coast. The man, a beggar most probably belonging to a Greek family, had longer arms than legs, as judged from the slope of the hill, and from the report in Childs’s book. He also probably belonged to a consanguineous family, since the Greek population lived in isolation in this region of the Black Sea coast, with many possible interfamilial marriages. Although he could not stand up without assistance, he was a man with rather strong arm and leg muscles, and could easily spring onto his donkey’s back. This man is depicted in Fig. 2. This case was the first adult quadruped man exhibiting Uner Tan Syndrome (UTS) with quadrupedalism, possible mild mental retardation, and dysarthric or no speech (see Tan, 2010a for a review). The arm to leg ratio (calculated from the picture) was rather high, 92%, similar to the arm: leg ratio of 90% in one case with UTS in the Adana 1 family (see Tan, 2006b, c).

Children with habitual quadrupedal locomotion were first reported by Hrdlicka (1928): 41 children (59% males, 41% females). The children began to walk on all fours at the age when healthy children begin to crawl on hands and knees. Some of them were later able to stand and begin to walk bipedally, but others continued walking and running on all fours for a long time. Fig. 3 depicts native African children running around on all fours. Their quadrupedal locomotion seems to be their natural gait, with easy and fast running. Fig. 4 depicts children with diagonal-sequence quadrupedal locomotion (right) and moving down or up stairs on all fours (left) (Hrdlicka, 1931, pp. 29 and 109).

Interestingly, not a single case with quadrupedalism was reported after the Childs’ case (see Childs, 1917) until the discovery of the Turkish quadrupeds, almost 100 years later (Tan, 2005, 2006a). These individuals exhibited a never previously reported novel syndrome, referred to as Uner Tan syndrome (UTS), with the main symptoms of habitual locomotion on all fours, mental retardation, and impaired speech (Tan, 2005; Tan 2006a). Subsequently, nine more families with this syndrome have since been reported in Turkey since the discovery in 2005 (see Tan, 2010a for a review). The clinical and radiological characteristics of these cases are presented in Table 1. The syndrome has sparked a world-wide interest: see, for instance, Garber (2008), Ghika (2008), Caglayan (2008, Thesis), Akpinar (2009), Le Fanu (2009), Held (2009), Kolb (2009, Thesis), Kutty (2010), Bornstein (2010), Pribut (2010), Downey (2010a, b), MacLellan et al. (2011), Arif et al. (2011).

Transient quadrupedalism 
The most prominent characteristic of the UTS cases was the diagonal-sequence quadrupedalism, which usually started during childhood following a normal hand-knee crawling period at around two years of age. However, a transformation from well-balanced quadrupedalism to ataxic-bipedalism occurred at around 12 years of age in one man, who walks in a bipedal ataxic manner now and has not utilized locomotion on all fours since about 25 years ago. The man was one of six quadrupedal cases in the first discovered family near Iskenderun (Tan, 2005; Tan, 2006a), and the five other cases in the family are consistent quadrupeds. 

In addition to this case one man (44 years old) from the Adana 1 family (Tan 2006b, c) exhibited consistent quadrupedalism, while the other man (34 years old) from the same family transformed from childhood quadrupedalism to ataxic bipedalism at about 14 years of age. In childhood this individual propelled himself backwards on his bottom, and then started ambulation on all fours at about two years of age. These persons with adulthood transformation from quadrupedalism to bipedalism were previously reported as consistently bipedal-ataxic cases. Consequently, these results concerning transient quadrupedalism are not consistent with some minor reports accentuating the existence of purely ataxic bipedal cases among siblings of UTS cases. A transformation from balanced quadrupedalism to ataxic bipedalism also occurred during adulthood. For instance, one of the brothers from the Kars family (now 46 years of age) exhibiting UTS, showed a transition from habitual quadrupedalism to ataxic bipedalism about 20 years ago. (seeTan, 2010b).

Dynamics 
Dynamics in physics deals with the motion and equilibrium of systems under the action of forces, usually from outside the system; it is an interdisciplinary field in contemporary science now, to analyze the behavior (Strogatz, 2000, p. 2). The system concept, accentuating the relationships between component parts rather than the parts themselves, opened a powerful new perspective in science. The system thinking is valuable because it can help us to create smart, enduring solutions to scientific questions, and because it offers us a more accurate picture of reality. By definition, a system is a group of interacting and interdependent components that form a complex and unified whole.

Systems can be controlled or uncontrolled. In controlled systems, the information is sensed, and changes are effected in response to the information, a process that can be referred to as detector, selector, and effector, respectively (Kuhn, 1974). The detector is the sensing part of the system, and is concerned with communicating information between systems, including environment. The selector is the part of the system that processes information and makes decisions, and the role of the decision-making part of a system is to drive the system towards equilibrium. The effector is responsible for the transactions between systems. Communication and transactions are involved in interactions between systems. From two general approaches, cross-sectional and developmental approaches, a system developmental approach was the topic of the present work, dealing with the changes in the system over time. To analyze the development of human quadrupedalism, a holistic analysis was performed to examine the system as a complete functional unit, instead of a reductionist approach, which looks downward and examines the subsystems separately within the system. Properties of any system are: (i) a system consisting of interrelated and interacting parts exists in an environment; (ii) any system has a preferred state; (iii) the components of a system may in turn be systems themselves. Conceptual systems are utilized in analysis, comprehension, and for improvement purposes. All open and closed systems have a preferred state. For instance, atomic oxygen prefers to be molecular oxygen, a business prefers to be profitable, human beings prefer to be physiologically and emotionally satisfied.

Complex systems and self-organization 
Complex biological systems, such as families, the human body, the brain, etc., consist of interconnected or interwoven parts (Bar-Yam, 1997, p.1). Complex systems in physics, such as ice crystals, galactic spirals, clouds, or lightning flashes, tend to spontaneously generate new organized forms. Dynamic complex systems have self-organizing properties, following the principle the sum of the parts is greater than the parts taken independently, contrary to Sir Isaac Newton’s argument the motion of the whole is the sum of the motion of all the parts. The dynamic complex systems have the tendency to spontaneously self-organize themselves to produce novel patterns. The process of self-organization is the quintessence of all living systems. 

The evolution of living beings may also be associated with the principles of self-organization, but Darwinism essentially ignores the process of self-organization (see Waldrop, 1990; Oudeyer, 2006). The self-organization is closely coupled with “emergence,” a fundamental property of complex systems, i.e., a new property or behavior…emergence may be considered the product or by-product of the system… the product of interconnections and the interaction makes it dynamic and unpredictable (Dobrescu & Purcarea, 2011). 

The emergence of unpredictable outcomes within a complex system such as the human body is closely related to neural networks that are “self-organized critically” (Tetzlaff et al., 2010). By definition, self-organization occurs through the interaction of its components (endogenously) or by some environmental influence (exogenously). self-organization may be triggered by “strange attractors” , which refers to a kind of steady-state in a dynamical system. One type of attractor is the strange attractor, which may be visible, for instance, in the EEG pattern during rest. Another type of strange attractor may be visible in the EEG during thinking. Other types of strange attractors may be consciousness and personality. 

The brain as a dynamic system may have many strange attractors, which may show state transitions, thereby creating novel and unpredictable patterns, such as during the postnatal development of children. The common factor for UTS to trigger a strange attractor, i.e., the diagonal-sequence quadrupedal locomotion may be their disability or difficulty in achieving bipedal upright locomotion. The extremely rare emergence of human quadrupedalism may be associated with the unpredictability of the strange attractors. Concerning the adaptive motor behavior and intentionality, the dynamical systems tend to control the outcome pattern of the system to find a compromise between which patterns can possibly be built from the system components to begin with, and the structural constraints of the environmental situation; a synergetic pattern formation—with possible strange attractors—may be “intentional” with the selforganization phenomena being basic explanations for the adaptive behavior (Tschacher et al., 2003).

Central pattern generators 
Central pattern generators (CPG) are embedded within the spinal cord, responsible for creating a locomotor pattern and generating rhythmic locomotor activity, without being controlled by the supraspinal centers (Grillner & Wallen, 1985; Hooper, 2000; Hiebert et al., 2006). The isolated spinal cord in the lamprey (a primitive fish) can spontaneously produce fictive locomotion (Cohen & Wallen, 1980; Grillner & Wallen, 1985), as in salamander (Delvolvé et al., 1999) and frog embryos (Soffe & Roberts, 1982). In contrast to lower vertebrates, the existence of CPGs in higher primates is much less convincing (Duysens et al., 1998), and the concept of CPG did not find supporters among system theoreticians. 

The progressive maturation of the locomotor networks (CPGs) in the central nervous system, studied by anatomical and electrophysiological techniques, was previously evaluated by Dr. Douglas Stuart, in a detailed review article (Stuart, 2007). Regarding the spinal CPGs operating in human beings, there is only indirect evidence. Locomotor-like movements were recorded in human fetuses at 10 gestational weeks, and neonatal infants often exhibit stepping movements if supported (McGraw, 1945, pp.22-23). However, this first stepping ability subsequently disappeared for many months due to mechanical (Thelen & Fisher, 1982) or neuro-developmental factors (Forrsberg, 1985). 

On the other hand, the CPGs are not static, previously hard-wired, firmly established systems, but instead they are rather loosely organized neural networks under the influence of the dynamically changing chemical and/or sensory control, resulting with many newly emerged functional circuits (Selverston, 1988, cited by Kelso, 1995, p.243). In contrast to the theory of stage-like motor and cognitive development, the perspective of behavioral-motor development as a self-organized process seems to be more plausible to explain why and how infants walk within a particular environment (see for review Thelen & Ulrich, 1991). That is, a previously coded neural network, i.e., neural coding, seems to be unlikely, because of the lack of precise point-to-point wiring in the central nervous system with immense overlaps of dendritic and axonal arbors. The integrative neuroscience emphasizes the “inside-out” and “outside-in” approaches for the understanding of locomotor control (see Stuart, 2007).（essay代写)

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