first_img The mechanisms underlying rhythmogenesis and large-scale patterning — for example, left–right alternation of body wall muscles in vertebrate swimming, stance-swing alternation of flexor and extensor muscles in stepping — have thus been elucidated in many model systems. It is important, however, to stress that the fine patterning and coordination of individual muscle groups within single cycles — for example, the dorsal fins in lamprey swimming, the precise timing of extensor muscles in single extensions during stepping — are less understood. Nose codes:  One of the most complex of our senses is the sense of smell – the olfactory sense.  The reason is that the nose has to be able to sort through an almost infinite variety of odorants, identify those of interest, and communicate that information to the brain for the appropriate response.  Olfactory organs are often highly sensitive.  Insects have incredible sensitivity to certain odorant molecules, such as pheromones and nectars.  Higher animals such as dogs and bears are also renowned for their ability to detect and memorize scents.  What scientists did not realize till recent years is that olfactory organs perform their magic by means of codes. It’s easier to study olfaction in insects, so that is what biologists have studied most (see “Nose Knows More than Math Pros Suppose,” 06/26/2005).  Undoubtedly, olfaction in vertebrates is much more complex, but functionally equivalent organs and processes in mammals have been identified.  Gupta and Stopfer, writing in Current Biology,1 used the word code twice in their headline: “Olfactory Coding: Giant Inhibitory Neuron Governs Sparse Odor Codes.”  They wrote about how odor information is encoded at several stages on the way from receptor to brain.  The method is remarkable, as they summarized in their opening paragraph: Brain mechanisms have evolved to gather and organize sensory information. This information does not flow passively from the outer environment through neural circuits, coming to rest as memories or actions. Rather, information is encoded, processed, and dramatically transformed in myriad ways as it travels through the brain, providing multiple advantages to the animal. For example, in many species and brain areas, sensory stimuli elicit dense bursts of action potentials from neurons in peripheral structures, but sparser firing in more central structures. Olfactory coding condenses initial bursts of odor information into manageable categories.  The pattern of initial bursts of peripheral neurons called Kenyon cells causes characteristic responses in the central structures, as if to sort responses by type.  It would be as if a dozen different signals from a flagman could trigger a single danger response.  But what happens is much more complex, with feedback and feed-forward signaling between the organs.  In addition, the information-compacting central structures respond differently if the incoming signals are synchronized.  The central structures appear tuned like a compressor-limiter to require thresholds before passing the information forward. Gupta and Stopfer reported that recently a giant neuron named GGN with “enormous, sweeping arborizations in the input and the output areas” appears to play a big role in information compression in insect olfaction.  This neuron takes input from every Kenyon cell, processes it like a computer, and can then inhibit the inputs.  According to the study, this giant neuron “responded to all tested odors with graded potentials that increased in amplitude along with the concentration of the odor.”  As a result, discrete inputs (molecules), by passing through the layers of information density and compression, yield a continuous output while simultaneously regulating further inputs.  In addition, another neuron tunes the giant neuron’s effectiveness, which in turn can be inhibited by the giant neuron.  Gupta and Stopfer said it’s like the input neurons turn a dial, another neuron regulates the dial’s sensitivity, and the GGN neuron, like a central processor, can choose what to do with the information and control the upstream inputs. In their final paragraph, Gupta and Stopfer said that these insect studies are shedding light on vertebrate olfaction.  Using language that sounds like electronic engineering, they could only refer to evolution in a negative sense (“evolutionarily conserved” means unevolved): The discovery of GGN’s powerful effect on Kenyon cells will reshape our understanding of olfactory coding in higher brain regions. How it works in the context of other sparsening mechanisms, such as the feed-forward inhibition pathway mediated by the lateral horn, will be interesting to determine . Combinations of feed-forward and feed-back inhibition have been observed in the vertebrate olfactory system: Stokes and Isaacson recently showed that a feed-forward inhibition mechanism acts immediately upon stimulus onset, and a feed-back inhibition mechanism contributes more slowly, in slices of the piriform cortex, a brain region in many ways analogous to the invertebrate mushroom bodies. And, in Drosophila, Papadopoulou et al. recorded from the APL, a neuron similar in structure to GGN, and found that the two neurons are functionally equivalent. Thus, global normalization mechanisms for maintaining sparse olfactory codes appear to be common. The relatively simple nervous systems of insects will no doubt continue to pave the way for unraveling the evolutionarily conserved mysteries of olfaction. Gupta and Stopfer, “Olfactory Coding: Giant Inhibitory Neuron Governs Sparse Odor Codes,” Current Biology, Volume 21, Issue 13, R504-R506, 12 July 2011. Move it:  How do we move?  Watch sprinters running down a track, weightlifters hoisting massive barbells, divers twisting in mid-air.  Obviously the central nervous system (CNS) is involved along with muscles.  A hint of the complexity in simple everyday movements can be gleaned from excerpts of a review in Current Biology by German and Swedish researchers.3  Once again, whatever we know is just the tip of an iceberg: Tubes constructed from single-layered sheets of epithelial cells (which line body surfaces and cavities) provide the structural basis for many internal organs. These tubes assume diverse forms, from the 25-foot-long, highly coiled intestine, to the elaborate branched networks of the lung and kidney. Even the brain and heart arise from simple epithelial tubes. Each tube must attain the precise length and diameter required for its physiological function, and creating tubes that bend, coil, branch, or twist requires additional regulatory mechanisms or modes of cellular force production. A major challenge for developmental biologists studying organ formation in the embryo, and for tissue engineers who aspire to build organs in the lab, is to understand how the molecular-level control of subcellular forces leads to tissue-level control of epithelial tube size and shape.  Two papers in this issue … address this challenge. They provide new insight into the cellular processes that make the right tube to fit the job. The first paper, attempting to figure out how airway tubes branch, described growth factors that determine the axis of cell division, giving preference to the long axis.  But these factors are regulated by complex feedback loops that govern their actions, turning them on and off at the proper times.  The second paper tried to figure out how tubes twist.  Again, growth factors were identified that preferentially push daughter cells in certain directions, but there were other factors that could cause bending of individual cells and tissues without cell division. It is clear that the researchers are barely beginning to understand tube formation.  The meager hypotheses in the two papers leave many questions unanswered: such as how a flat sheet of epithelium curves and joins into a tube; how the tube diameter and thickness are controlled; and how all the accessory cells such as sensors, blood vessels and nerves and other organs find their proper locations in and around the tube.  Giving a phenomenon a name like “morphogenesis” is not the same as understanding it.  The authors know that; “These studies signal a growing trend in which classical molecular and genetic approaches merge with quantitative microscopy, image analysis, and modeling to provide new insights into the cellular dynamics of tissue morphogenesis,” they boasted, quickly adding a reality check: “It is likely, however, that we are seeing just the tip of an iceberg.” From genes to tubes:  We have lots of tubes in our bodies: blood vessels, intestines, airways, ducts.  How can a genetic code take dividing cells and build them into tubular structures?  This question was asked in Science this week.2   Sally Horne-Badovinac and Edwin Munro from the University of Chicago described the problem: A major challenge for neuroscience is to determine how central nervous system (CNS) activity is causally related to behaviour. Motor behaviours are generated by task-specific CNS neural networks. Sally Horne-Badovinac and Edwin Munro, “Developmental Biology: Tubular Transformations,” Science 15 July 2011: Vol. 333 no. 6040 pp. 294-295, DOI: 10.1126/science.1209687. Motor behaviour results from information processing across multiple neural networks acting at all levels from initial selection of the behaviour to its final generation. Understanding how motor behaviour is produced requires identifying the constituent neurons of these networks, their cellular properties, and their pattern of synaptic connectivity. These brief looks at just three aspects of body language – olfaction, development and movement – illustrate how scientists find layers of complexity wherever they look.  Now add the endocrine system, digestion, reproduction, circulation, the skeletal system, the sensory organs, and all the other systems, package them all in skin and operate everything with a three-pound brain that runs on potatoes, and you begin to fathom the wonder that is you. Your body is speaking to scientists.  Some of them hear it saying evolution.  Others think it says intelligent design.  What characteristics would each side expect?  Most people intuitively know design when they see it.  Here are three recent scientific papers that may help interpret body language. Movements are produced by multiple neural networks, including high-level networks that ‘decide’ if movement is appropriate, those that determine the general characteristics of the movement (for example, direction, limb or body velocity), and the (often segmental) neural networks that generate the detailed motor neuron activity that drives the locomotor organs (typically muscles). Buschges, Scholz and El Manira, “New Moves in Motor Control,”  Current Biology, Volume 21, Issue 13, R513-R524, 12 July 2011. These papers present, once again, a pattern we find often in scientific papers: the more detail, the less evolution talk.  Only one of the three papers even mentioned evolution, and that instance was pathetic: “Brain mechanisms have evolved to gather and organize sensory information.”  That was the opening sacrifice to Charlie in the olfaction paper.  Ask yourself; did that little piece of worldview self-affirmation provide any understanding to the subject matter?  The whole rest of the paper, for crying out loud, was about codes, mechanisms, fine-tuning, signal processing and layers of information.  Those are the same authors who provided that other Darwin gem in their last sentence: “The relatively simple nervous systems of insects will no doubt continue to pave the way for unraveling the evolutionarily conserved [i.e., unevolved] mysteries of olfaction.”  That was it.  Those were the only two mentions of evolution in these three amazing papers.  Darwinists, if you can’t do better than stating your dogmas as bookends to papers that scream intelligent design, don’t be surprised when growing numbers of people find Charlie’s little myth unconvincing.  The rest of us, hopefully, were inspired to thanksgiving, if not worship, for the unfathomable treasures we have been given for our earthly dwellings.  Appreciating the design inside of you might just motivate you to take better care of your dwelling (see Science Daily and Psalm 139).(Visited 9 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

Leave a Comment

Your email address will not be published. Required fields are marked *