The Role of Theory in Advancing 21st-Century Biology Catalyzing Transformative Research (2008) / Chapter Skim
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8 What Determines How Organisms Behave in Their Worlds?
8 What Determines How Organisms Behave in Their Worlds?
Pages 130-144
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From page 130... ...
Understanding life requires determining the rules that govern how organisms behave in their worlds, how they sense their environments, and how they use this information to change their behavior. Organisms do not passively wait for information from their environments; rather, their physiology is internally generated, by genetically determined rules, and input from the environment is used to alter the behavior of the organism.
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From page 131... ...
For a single fertilized egg to develop into a highly differentiated and organized multicellular organism, individual cells must receive cues about their location and future role in the organism to migrate to the right place and differentiate into the appropriate specialized cell. As each of the organism's cells contain the same genetic material, the interplay between external cues, the triggering of various genetic pathways, and the subsequent modification of the cell to be able to respond to different external cues (e.g., by the expression of receptors or ion channels)
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From page 132... ...
4. How are representations of the external world combined with internally generated signals to allow the organism to integrate past and present stimuli to make decisions about relevant actions?
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From page 133... ...
, and while many signal transduction pathways are well characterized, those activated by many sensory modalities remain mysterious. A beautiful example of the interaction between physics and biology can be seen in elegant work elucidating the fundamental mechanism by which sound results in hair cell deformation and changes in membrane conductances (Hudspeth, 2001; Chan and Hudspeth, 2005a, b; Hudspeth, 2005; Keen and Hudspeth,
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From page 134... ...
Because animals do not spend their lives experiencing pure, well-defined stimuli, investigators are beginning to ask how sensory systems respond to natural stimuli, which change in complex and unpredictable fashions. This is much more difficult than working with simpler stimuli, as it requires characterizing the properties of the stimuli and understanding how they are captured in a spike train or a series of spike trains.
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From page 135... ...
Across biological scales, the response to environmental cues can differ depending on the state of the cell or organism. Whether people experience a stimulus as painful depends to a large degree on prior history with the stimulus, expectation of its duration, and whether it is viewed as innocuous or as a portend of dire consequences.
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From page 136... ...
This has been termed the "jamming avoidance response" and is biological bandwidth sharing that allows multiple animals to navigate simultaneously. The jamming avoidance response of electric fish.
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From page 137... ...
, and theoretical approaches may identify common features of these mechanisms. Box 8-1.2 3. How is past experience represented in the internal state of the organism?
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From page 138... ...
Wild tobacco plants growing within range of the chemical signals will also stimulate the defense mechanisms they use to repel plant-eating insects like caterpillars. SOURCE: Baldwin et al.
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From page 139... ...
Although the molecular and cellular mechanisms underlying stable changes in synaptic transmissions have progressed dramatically in the past decade (Kandel, 2001) , even at the subcellular level, much remains to be understood that
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From page 140... ...
The reason appears to be that some seeds that have experienced a period of light deprivation up-regulate an extremely sensitive light receptor that can detect minute flashes of light and trigger germination (Scopel et al., 1991)
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From page 141... ...
. Today, models of how the brain stores memory incorporate many more recently discovered biological details in order to understand memory storage in real biological networks.
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From page 142... ...
The most crucial of these for life are the respiratory centers that drive breathing. Of course, sensory inputs modify the output of respiratory and other central pattern generating circuits, as is necessary for the animal to adapt its internally generated movements to its needs in the world.
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From page 143... ...
THE IMPORTANCE OF THRESHOLDS A characteristic feature of many of these biological processes is that they have specific thresholds, such that stimulus intensities below threshold fail to result in a response, while higher stimulus intensities produce responses. This kind of threshold is a characteristic feature of the action potential, the unit of most electrical signaling in the nervous system, but threshold behavior and amplification can also result from many signal transduction cascades, such as those triggered by hormones in individual cells.
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From page 144... ...
. Recognition of the deep evolutionary roots of sensory pathways provides opportunities for collaborative theoretical and experimental research combining neuroscience, microbiology, and plant and animal physiology.
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