2015_fall_BBio_351_lab_6.docx - BBio 351: Principles of...

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BBio 351: Principles of Anatomy & Physiology IFall 2015Lab 6: Earthworm action potentialscreated by Doug Wacker with materials provided by ADInstruments;revised by Greg CrowtherToday’s objectivesMake extracellular recordings of action potentials from anesthetized earthworms.Use these recordings to explore four core concepts of neurophysiology: threshold, “all-or-none” responses, nerve conduction velocity, and refractory period.Supplies/equipmentLabChart 7.1 softwarePowerLab Data Acquisition Unit with Bio AmpStimulator Cable (BNC to Alligator Clips)5 Lead Shielded Bio Amp CableShielded Lead Wires (3 Alligator Clips)Three silver wires, chlorided at one endModeling clay or adhesive tapePetri dishMillimeter rulerTissuesBlunt probeDissection tray with wax or padDissection pinsEyedropper or Pasteur pipetteOne earthworm (Lumbricusspp.), at least 60 mm in length10% ethanol in earthworm salinePre-lab assignmentBy the start of your lab section (Tuesday at 2pm, Thursday at 2pm, or Friday at 8:45am) youshould (1) print or download this lab handout, read it over, and bring it to lab; and (2) completethe pre-lab assignment posted to Canvas (which will include questions on the material below).BackgroundA characteristic of the nervous system is that signals are conducted from place to place bynerve impulses – action potentials that travel along a nerve fiber, or axon.All sensation,thought, and movement is mediated by coded patterns of nerve impulses.The properties ofaction potentials in single fibers are therefore of fundamental physiological importance.Annelids, such as the common earthworm (Lumbricusspp.), and arthropods have a ventralnerve cord that is analogous to the dorsal spinal cord of chordates.The earthworm possessesa medial giant nerve fiber and two lateral giant nerve fibers (that lie on either side of the medialone) that run the length of the animal.The earthworm also has a multitude of small nerves thatdo notrun the length of the animal (there are about 500-1000 neurons per segment, or about100,000 neurons altogether).Each giant fiber is actually made up of multiple large cells (oneper segment) that are electrically coupled to each other throughgap junctions.This results inthe rapid conduction of action potentials from cell to cell so that each giant fiber behaves almost1
BBio 351: Principles of Anatomy & Physiology IFall 2015

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Term
Fall
Professor
LIU
Tags
Alligator Clips, Stimulator Panel

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