Megan Cody 10/23/12 Professor Mirshams Biol 2401. PL2 Neurophysiology of Nerve Impulses IntroductionIn this report, it’s discussing the effects of various agents on nerve transmission and what kindsof stimuli trigger an action potential. A nerve cell usually is polarized due to an unequaldistribution of ions on either side of its membrane. When such a polarized membrane isstimulated at or above its threshold intensity, a wave of action potentials is triggered to movein all directions away from the site of stimulation. This wave constitutes a nerve impulse, and ifit reaches a muscle, the muscle may respond by contracting (Marieb, 125). In this experiment asegment of a nerve has been dissected and suspended over a series of metal bars that act aselectrodes. The two electrodes at the bottom are stimulating electrodes and are connected toan electrical stimulator. The stimulator can be used to apply electrical current to the nerve atdifferent voltages and frequencies to try to elicit an action potential. The other set of electrodesare called recording electrodes, and they are connected to an oscilloscope. Differences incharge between the two recording electrodes cause the line traced on the oscilloscope screen
to deflect. Thus, we can observe any action potentials forming in the nerve.(Marieb 130-131)From the information gathered from the experiment I predict that high voltage will triggeran Action Potential and all the agents will generate some kind of response on the nerve.MaterialsElectric Stimulation:NerveNaClHCIOscilloscopeRed Electrical LeadsBlack Electrical LeadsNerve ChamberStimulatorInhibiting a Nerve (computer generated)NerveCurare
EtherOscilloscopeRed Electrical LeadsBlack Electrical LeadsNerve ChamberStimulatorMethodsIn the Electrical Stimulation lab we first set the Voltage on the Oscilloscope to 1.0V then clickedon stimulus button to see the response. If there was no response, the voltage was increaseduntil action potential was reached. The voltage was then increased by .5V until there wasfurther peak of the action potential trace.In the chemical Stimulation lab put a couple drops of NaCl on the nerve to see if it wouldgenerate an action potential. The Voltage was then changed back to 3.0V to see if the newtracing differed from the original threshold tracing. The nerve was then cleaned. A couple dropsof HCI were added to the newly cleaned nerve to see if it would generate an action potential.In testing the effects of ether experiment, a couple drops of ether were added to the nerve. Thevoltage was then set to 3.0V and the trace was observed. The time on the oscilloscope was thenchanged from msec to min and the Interval between Stimuli was changed to 2 mins. The time ittook for the action potential to return to normal was then observed.
In the testing the effects of curare, a couple drops of curare were dropped onto a clean nervebetween the stimulator and electrodes. The voltage on the stimulator was then set to 3.0V.Then the stimulus was tested to see if it would have an action potential.Results and Discussion Voltage Glass Bar NaCl HCI Action Potential 3.0V - - - Yes 5.5V - - - YesFigure 1.1 Comparison of first reaching Action potential and maxing out on action potential.Voltage Glass Bar NaCl HCI Action Potential3.0V - - Yes Yes3.0V - Yes - YesFigure 1.4NaCl versus original action potential.Voltage Ether Curare Lidocaine Action Potential3.0V Present Absent Absent No3.0V Absent Present Absent YesFigure 1.5Ether and Curare versus original Action Potential
Graph 1.1 Increasing voltage and maxing out of Action PotentialThe experiments went as expected with no unusual events that would have introduced error. Inthe experiments a sciatic nerve from a frog was used. The leads that were placed o there forfrom the stimulator output to the nerve chamber and also to the oscilloscope. The current thatit produces then travels to the nerve. The nerve depolarizes and the electrical current that itdevelops continues to loop through the leads. So starting out the experiment the voltage wasset to 1.0V to see if an action potential happened and it didn’t. So by slowly increasing thevoltage it was found that at 3.0V was when the action potential could be first reached as shownin fig 1.1. Once the action potential was reached an increase of .5V was done to observe thedifference in the action potential. When increased there is a slight increase in the height of theaction potential peak because at the threshold voltage, the smaller fibers in a nerve arestimulated and an action potential is seen as in Graph 1.1. Increasing the voltage will cause
most, if not all of the neural fibers to undergodepolarization. A given nerve is made up ofliterally thousands of neuron processes(axons) so this slight increase is noted when all fibers inthe nerve fire (willison 5). Another part of the experiment was chemical stimulation. NaCl andHCI were added to the nerve to observe the action potential it might produce. Both the HCI andthe NaCl produced action potential as seen in fig 1.4. Another experiment was also done to testthe effect of ether on the sciatic nerve. When a couple of drops were placed on the nerve andwas stimulated no action potential was noticed. No action potential was made because theether ananesthetized the nerve which shut down all neuron to neuron communication(Britannicca 2) as in fig 1.5. The last experiment performed was curare on the nerve. Curare is aplant in South America typically used to cause paralysis in prey (Marieb 131). A couple dropswere placed on the nerve then stimulated to see if an action potential is formed. No actionpotential was formed because nerve propagation is unaffected because curare works on thesynaptic ends of the nerve as in fig 1.5. From the effect of the curare on the nerve it’s clear tosay that Curare would ultimately kill an organism by blocking nerve transmission. It’s clear tosay that all electrical and most chemical stimulation are capable of generating an actionpotential in the nerves.ConclusionIn the labs performed we discover some of the stimuli that caused action potential and effectsof various agents on nerve transmissions. Everything worked the way it was supposed to. Welearned of some agents that prevent the neuron to neuron communication and which
ultimately didn’t cause any action potential. In future experiments more agents could be usedto manipulate the nerves a little more and see the reaction of the action potential.
ReferencesMarieb, Elaine N., and Susan J. Mitchell. "Neurophysiology of Nerve Impules: ComputerStimulatiom." Human Anantomy& Physiology.N.p.: n.p., n.d. 125-33. Print."Nerve impulse".Encyclopædia Britannica. Encyclopædia Britannica Online.Encyclopædia Britannica Inc., 2012. Web. 23 Oct. 2012<http://www.britannica.com/EBchecked/topic/409616/nerve-impulse>.Willison, Anna. "What Is an Action Potential? (Nerve Impulse)." What Is an Action Potential?(Nerve Impulse). AAMRICIRE, 12 Nov. 2010. Web. 23 Oct. 2012. <http://antranik.org/what-is-an-action-potential-nerve-impulse/>.