Action Potentials In Squid Axon

Action Potentials In Squid axoneIn 1952, Hodgkin and Huxley published a series of four papers in the ledger of Physiology (London) reporting their experiments to investigate the underlying events of the movement capability. In their final paper, they derived a series of equations that describe the relationship between atomic number 11 conductance (gNa+), potassium conductance (gK+) and the tissue layer latent in a squid axon following galvanising arousal. Hodgkin and Huxley were awarded the Nobel Prize for this work.In this practical, you impart use a computer computer program based on the Hodgkin and Huxley equations to show what is happening to the membrane voltage, gNa+ and gK+ during and subsequently electric stimulation. An ideal of the output from the program is illustrated in figure 1. It nominate be seen that the galvanising stimulation depolarises the membrane. Once a depolarisation of 30mV has occurred, the conductance to sodium ions pluss rapidly and th e membrane cap qualifiedness drop rises to +20mV. The rise in gK+ is s tear down in intrusion and lasts for longer than the append in gNa+. The fall(a) in gNa+ and the associated rise in gK+ returns the membrane capability towards the resting value.Figure 1 trick of spays in membrane strength, Na+ and K+ conductances following the application of a virtuoso electrical stimulant drug of 50 A/cm2 for 1ms. The peak height, amplitude, rotational re motion time and door of the fulfil potency ar shown.Methods and ResultsRun the Squid Giant Axon model from the Start menu, HHX.Experiments using a single electrical input signalIn the first base series of experiments, you will use a single electrical comment to initiate an attain potential. Run a simulation with the following parameters stimulant 1 Amplitude (A/cm2)comment 1 eon (ms) clench (ms) input signal 2 Amplitude (A/cm2) stimulation 2 term (ms)501000A trace analogous to figure 1 will be obtained. From this trace, you can measure the peak height, amplitude, latency and threshold of the put through potentialPeak Height(mV)Amplitude(mV) reaction time(ms)Threshold Voltage (mV)+191090.46-66Q1 and 2. Investigate the orders of varying comment amplitude and duration by running all the simulations shown in the matrix below in dishearten 1 Enter a X in the control board 1 matrix for experiments that produce an action potential, and memorialize the peak height, amplitude, latency and threshold of each action potentials in Table 2 overleaf. For experiments that fail to sex an action potential, code a O in the matrix below, and record a value of ( mlessness) for the latency and - for the other parameters in the table overleaf.Table 1. Success/failure matrixStimulus Strength (A/cm2)Stimulus continuance (ms)0.10.512550OXXXX20OXXXX10OOXXX7OOXXX5OOOXX2OOOOOTable 2 Action potential characteristicsStimulusResponseStrength(A/cm2)Duration(ms)Peak Height(mV)Amplitude(mV)Latency(ms)Threshold Voltage ( mV)20.10.512550.10.512141042.89-615151052.74-5970.10.51121024.38-572151052.16-585161062.16-57100.10.51151052.01-612161061.62-645161061.62-64200.10.5151051.58-641161061.02-632171070.97-665171071.04-61500.10.5171070.59-611191090.54-602191090.52-625191090.57-58Q3. Plot two graphs to show the relationship between (i) Stimulus effect and latency and (ii) Stimulus duration and latency.How these graphs should be plotted is non immediately obvious, and information on how to complete this task will non be explicitly given The optimal solution to the problem is for you to find, but the following points be interpretd for guidanceIt is non legitimate to plot infinity on graphsIt is non appropriate to extrapolate beyond data pointsIt is not legitimate to plot average latencies. The graphs must be plotted so that every value of latency (except ) is represented.Use the blank sheet on the proforma, at that place is no need to use graph paper. represent 1 Stimulus medium and latencyRememb er you need to distinguish distinct stim durations in this grGraph 2 Stimulus Duration and Latency reach sure you distinguish different strengths as wellThese can be plotted accurately using excel for your submitted report.Experiments with dual stimuliQ4. Run a simulation with the following parameters to demonstrate the absolute heady intentSimulationStimulus 1 Amplitude (A/cm2)Stimulus 1 Duration (ms)Delay (ms)Stimulus 2 Amplitude (A/cm2)Stimulus 2 Duration (ms)A500.54500.5B500.541000.5Briefly describe the responses obtained in simulations A and B in the space belowIn A the first and bit foreplay is equal. The first stimulus arranges an action potential whilst the s stimulus does not. The ride out is only 4ms. The membrane is at the absolute stubborn plosive when the succor stimulus is sent. therefore an action potential cannot be produced. The first stimulus for A causes the gK value to change from -0.36 to 6.0. The gNa, 0.01, does not increase for the encourage st imulus and the peak reached is -92mV for the back up stimulus and the threshold is -52mV.In B the second stimulus is larger than the first one but the determine re importants the same at 4ms. The increase of the stimulus does not cause an action potential. This suggests it must be in the absolute unregenerate layover because a larger stimulus should be able to generate an action potential if it is in the relative refractory completion. The value of gK changes from -0.36 to -5.87. The peak was -83mVQ5. buy up the simulations, but with a longer agree between stimuliSimulationStimulus 1 Amplitude (A/cm2)Stimulus 1 Duration (ms)Delay (ms)Stimulus 2 Amplitude (A/cm2)Stimulus 2 Duration (ms)C500.57500.5D500.571000.5Compare and contrast the responses obtained in simulations C and D with those of A and B.Stimulation C and D has a longer delay between the first and second stimulus than stimulation A and B. Stimulations C has a lower second stimulus than D but the same as A. Likewise f or Simulation A which has a lower second stimulus than B. Stimulation B and D have got the same amplitude for the second stimulus. The second stimulus, like A, for simulation C did not generate an action potential. Whilst with simulation D, unlike B, an action potential was generated. This is because in the absolute refractory period it is not possible for an action potential to be generated indeed why simulation B did not produce an action potential. The delay in stimulation C and D is longer therefore the membrane is in the relative refractory period. This is suggested by the action potential produced in D. The extra delay in D enables more inactivation supply to dissonant generating an action potential. The larger amplitude in D caused the membrane to reach threshold.DiscussionAnswer the questions below in the spaces provided. This will provide the basis of your report discussionQ6. Briefly justify why a latency of was recorded if an action potential was not produced.Latency is the time from the start of the stimulus to threshold. If no action potential is produced thus it is not ever possible for it to reach threshold, -59mV, therefore it has to be labelled as infinity because no matter how long you wait you will never reach threshold.Q7. What evidence from your results suggests that action potentials are threshold phenomena?Only the experiments which reached threshold value produced an action potential, refer to table one. For example when the strength of the stimulus is 2mA/cm2 no action potential was produced but the membrane potential did change however it did not reach threshold. When the strength of the stimulus was increased the, for example to 5 mA/cm2, and the duration of the stimulus as increased to 2ms past an action potential was reached. This is because the membrane must depolarise to the threshold level therefore generating an action potential with the same amplitude. This is the all or zero principle.Q8. Comment briefly on the amplit ude of the action potentials generated in these experiments.In all the experiments, table 2, which an action potential was generated, the amplitude was always alike even though the stimulus strength and duration had changed. This is part of the all or nothing principle. The amplitude was always around 106mV showing that action potentials are not graded. The frequence of the action potential is determined by the intensity of the stimulus. The frequency of action potential is caused during the relative refractory period. stratified potentials can be larger and last longer than action potentials. then during the relative refractory period if the graded potential is stronger than the threshold at resting then it will produce another action potential. If the graded potential last longer than the relative refractory period an action potential will also be generated. Both these factor effect the frequency of action potentials.Q9. From Graph 1, describe the effect of increasing stimulus strength on the latency of the action potential.The graph shows that the strength of the stimulus increases as the latency decreases. For example, when the stimulus strength is 5mA/cm2 and has duration of 2ms the latency is 2.89ms. When the stimulus strength is increased to 50mA/cm2 for the same duration of 2ms the latency change magnitude to 0.52ms. This shows that the latency has decreased by 2.37ms. Latency is the time from the start of the stimulus to the threshold. wherefore as the strength of the stimulus increases, the time for an action potential to be generated decreases.Q10. From Graph 2, describe the effect of increasing stimulus duration on the latency of the action potential.The graph shows a larger effect with the lower stimulus strength. For example if the stimulus strength is 50mA/cm2 and the duration is 0.5 the latency is 0.59ms and if the duration is 5ms the latency is 0.57. However, if the stimulus strength is 10mA/cm2 and the duration is 1ms the latency is 2.0 1ms and if the duration increases to 3ms the latency is 1.62ms. Latency is the time from the start of the stimulus to the threshold. because as the duration of the stimulus increases, the time for an action potential to be generated decreases.Sodium permeability increase in membraneNumber of sodium channel slack increaseQ11. attain a simple flow diagram to illustrate the positive feedback speech rhythm that results in the rapid depolarizing phase of the action potential.Activation gates openMembrane depolarisesStimulus causing to reach thresholdPositive feedback dedicate of cell increases causing depolarisationInflux of sodium into cell increaseQ12. What event at the ion channel level terminates the above cycle?1ms after the activation gate open the inactivation gate closes. This is a delay response of the depolarisation. The channel is now incapable of opening until it reaches near resting potential this is when the inactivation gate opens. Therefore the sodium channels closes and sodium ions savings bank enter the cell. Also the opening of the potassium channels helps terminates this cycle.Q13. What physiological mechanics is responsible for the absolute refractory period?Absolute refractory period is during the depolarisation and most of the repolarisation phase. At this point the sodium channels inactivation gates are closed and the activation gates are open. Therefore the channel is closed and incapable of opening so an action potential cannot be generated by another stimulus in this period.Q14. Explain your observations to simulations C and D in the Methods and Results section.Stimulations C have a lower second stimulus than D. The second stimulus, for C did not generate an action potential but simulation D did. The delay in stimulation C and D is long therefore the membrane is in the relative refractory period. This is suggested by the action potential produced in D because the larger stimulus amplitude. The extra delay in D, compared to B, enables more inactivation gates to open allowing. Also the larger stimulus allows another action potential to be generated.Q15. Briefly summarise two effects that refractory periods impose on the behaviour of neurones (N.B. restatement of the definitions of refractory periods is not what is asked here)There are two types of refractory period absolute and relative. During the absolute refractory period no action potential can be produced. In the relative an action potential can only be produced depending on the strength of the stimulus. Therefore there is a minimum delay required before a second action potential can be generated. Also it controls the frequency of the action potential generated. This period also helps ensure action potential can only move in one direction.Questions to answer after the practical.Q 16 . Most Local anaesthetics are Sodium channel blockers. Describe how these compounds work, the side-effects and what their main clinical uses are. ( max 300 words).Local anaesthet ics are weak bases which are used for loss of smart and muscle power so that a particular area of the body becomes numb. When sodium channel blockers, like lidocaine, enter the body it will be equilibrium with the tissue fluid. The anaesthetic will be in its ionised and non-ionised form. The non-ionised form will be able to pass through. It will be become partially ionised and deliver leave, ion trapping. The ionised form will bind to the sodium channel. This will block sodium ions from entering the cell and therefore it cannot be depolarised. As a result it does not reach threshold and an action potential is not generated. Consequently the nerve cells cant signal to the brain so pain cant be felt or muscle cant be moved. (Tuckley, 1994).There are many different local anaesthetic functional with the side effects differing for each drug and. The general side-effects can be, for example, numbness, sickness, lower blood pressure, light headedness and drowsiness. Not all of these ar e felt by the patient role. ( junction Formulary Committee (2010).The anaesthetic can be administered in by several methods, for example, a dentist will use an injection to the mouth. The effect of the anaesthetics will only be felt by the area in which it is injected in. Dentist will use local anaesthetic so that their patient will have loss of pain only in their mouth. Therefore the patient will not be able to feel any pain whilst the dentist carries out the procedure. It is also used for well-nigh nitty-gritty surgery and minor skin surgery. (Tuckley, 1994).ReferencingTuckley, J, M. (1994).The pharmacology of local anaesthetic agents, Pharmacology, 4, 7.Joint Formulary Committee (2010). British National Formulary. (59th ed.). London Pharmaceutical Press.Q17. will these compounds work if they dont block all the Na channels ? Why ?(Use your data-based data to help answer this question)During the relative refractory period just about channels are open allowing a second action pot ential to be generated. For example for stimulation D an action potential was produced for the second stimulus because the cell was in its relative refractory period. However for stimulation C an action potential was not produced for the second stimulus, even though the delay was the same. However the second stimulus was larger for D than C. Therefore if the compound does not block all the sodium channels then an action potential may be generated depending on the number of sodium channels blocked and the strength of the stimulus because the concept is very similar to the relative refractory period as some of the channels are not be open but in this case some channels are blocked. In both cases, relative refractory period and local anaesthetic, some channels allow sodium ions to enter the cell. As a result the compound will not work.