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Oligochaete Giant Axons

Oligochaete Giant Axons. Charlie Drewes Ecology, Evolution & Organismal Biology Iowa State University. What is an oligochaete?. What are giant axons?. ► disproportionately large-caliber nerve fibers. ► interneuronal in origin and function.

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Oligochaete Giant Axons

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  1. OligochaeteGiant Axons Charlie Drewes Ecology, Evolution & Organismal BiologyIowa State University

  2. What is an oligochaete?

  3. What are giant axons? ► disproportionately large-caliber nerve fibers ► interneuronal in origin and function ► unineuronal or multineuronal (some syncytial) ► rapidly conduct spikes ► mediate rapid, stereotyped escape reflexes (= ‘startle’ responses)

  4. Why are giant axons giant? ● to enhance conduction velocity, thus ensuring more rapid and more synchronous excitation of motorneurons & muscles throughout body ● to enhance “safety factor” for conducted spike (i.e., reduce “current loading” into electrically electrically coupled neuronal networks)

  5. GIANT NERVE FIBERS Group Examples diam m Main motor Response ----------------------------------------------------------------------------------------------------------------------------------------------------- Which organisms possess giant fibers? Group Example diam m Main motor Response ---------------------------------------------------------------------------------------------------------------------------------------------  --------------------------------------------------------------------------------------------------------------------------------------------------

  6. Lumbriculus variegatusCalifornia blackwormAnnelida (Oligochaetea)

  7. Lumbriculuscross-sections through ventral nerve cord

  8. Oligochaete giant fiber sheath and collaterals A giant fiber axoplasm D B FeCl3K4Fe(CN)6

  9. MGF Spike waveforms & sensory field maps LGF

  10. L L L M M M L L L

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