circuits for escape I_Giant neurons

circuits for escape I_Giant neurons - Giant axons innervate...

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Giant axons innervate circular muscles of the mantle causing them to contract http://porpax.bio.miami.edu/ ~cmallery/150/neuro/c8.48x 2.squid.jpg
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Anderson & Grosenbaugh, 2005 How squid escape: jet propulsion
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Squid show rapid stereotyped escape to a flash (A,B), but more delayed and variable escape to less intense stimuli (C = weak shock; D = odor cue. Record of mantle contractions of living tethered squid. Otis and Gilly, 1990
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Giant axon spike Left side Right side 66 msec Head retraction Mantle contraction Bilateral activation of giant axons causes rapid escape Otis & Gilly, 1990
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Implanted electrodes in squid show the giant axon initiates rapid escape; this circuit develops very early; smaller neurons fire later. Small neurons
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Squid also have a parallel circuit of smaller neurons for less vigorous escapes. They can recruit the giant axon along with the smaller neurons. Here are 3 cycles of mantle contraction. The mantle pressures from each cycle are overlain in the center. Note that the amount of contraction is greatest (cycles 1 and 3) when the giant axons are recruited along with the smaller neurons. Giant axon spike Small neurons
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Squid also use a parallel circuit for escape: Smaller neurons that are activated more slowly are used to complement the actions of the giant neurons for increased muscle contraction.
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More bang for your buck: squid also use giant axons to move rapidly to catch prey
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Juvenile squid were fed either fast- or slow-moving prey Prey not to scale. They are much smaller!! http://www.scubaduba.com/perina/perina_squid.jpg http://media-2.web.britannica.com/eb-media/20/12720-004-3F05363F.jpg http://www.naturamediterraneo.com/Public/data3/albert2006/Artemia Slow-moving brine shrimp Fast-moving copepods
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Myelination in copepods No nodes of Ranvier, but small patches of bare membrane along the axon Latency to escape (msec) w/out myelin ( Undinula vulgaris ) = 6 w/ myelin ( Pleuromamma xiphias ) = 2 Davis et al. 1999 Cross section of antennal (sensory) nerve EM view of axon
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lunge attack of squid. Chen et al. 1996
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circuits for escape I_Giant neurons - Giant axons innervate...

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