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Neuro Lab #2
Characteristic of the Action Potential
| Question | Answer |
|---|---|
| In simulation 1, you examined how intracellular and extracellular ________ and ________ concentrations affect the squid giant axon | sodium and potassium ion concentrations |
| Simulation 1: What were the effects of different extracellular Na+ concentrations on peak voltage? | [Na]o is directly related to peak voltage. As extracellular Na+ concentration increased, so did the peak voltage |
| Simulation 1: What were the effects of different intracellular Na+ concentrations on peak voltage? | [Na]i is inversely related to peak voltage. As intracellular Na+ concentration increased, peak voltage decreased |
| Simulation 1: What were the effects of different extracellular K+ concentrations on peak voltage? | [K]o is directly related to peak voltage. As extracellular K+ concentration increased, so did the peak voltage |
| In simulation 2, you examined another way to look at the length constant. Also, three variables and their affect on the passive spread of voltage were examined. What three variables? | membrane resistance, capacitance, and axon diameter |
| the length constant is used to describe the rise of ___________ difference across the membrane | potential |
| membrane resistance | force that impedes the flow of electric current across membrane |
| Simulation 2: How does the length constant change with membrane resistance? | (directly related) neurons with higher membrane resistance (fewer open channels) will have longer length constants |
| Simulation 2: How does the length constant change with axon diameter? | (directly related) neurons with larger diameter (lower axial resistance), will have longer length constants |
| Simulation 2: How does the length constant change with membrane capacitance? | (inversely related) neurons with high membrane capacitance will have shorter length constants.If membrane capacitance is decreased, propagation velocity and length constant increase |
| In simulation 3, you examined the mechanism that underlie propagation of the action potential along the axon, and observed the effects of changing axon diameter on impulse propagation and observed the propagation velocity of an __________ axon | unmyleinated |
| Simulation 3: changing the axon diameter caused changes in the amount of current required to stimulate the axon (impulse propagation). Explain | (directly related) a small axon diameter required less current to stimulate while a larger axon diameter delayed the action potential. |
| Simulation 3: What value was obtained for the velocity of propagation of an impulse in an unmyelinated axon? | only 1.82m/s |
| In simulation 4, you examined the mechanism of action potentials in a myelinated neuron. You compared the velocity of action potentials for myelinated and unmyelinated axons. What else did you examin? | how the amount of myelin affects conduction velocity |
| Simulation 4: What value was obtained for the velocity of propagation of an impulse in a myelinated axon? | 19.03 m/s |
| Simulation 4: How do the myelinated and unmyelinated axon compare in propagation velocities? | the myelinated axon had a much larger velocity than the unmyelinated axon |
| Simulation 4: What was the effect of different amounts of myelin wrapped around the axon on conduction velocity? | (directly related) as number of myelin wraps increased, so did the conduction velocity |
| In simulation 5, you examined how a current pulse changes the voltage across a membrane under various circumstances and how these things effect _________ | capacitance |
| Simulation 5: effect of current pulse on voltage across a membrane. In the graph, what is the slope of the ramp? | change in voltage |
| simulation 5: how is the change in voltage across a membrane related to the current pulse? | they are directly proportional, as the current pulse increases, the slope of the ramp (change in voltage) also increases |
| simulation 5: how is the change in voltage across a membrane related to capacitance? | they are inversely proportional. as the capacitance increases, the slope of the ramp (change in voltage) decreases. |
| simulation 5: what is the Hodgkin and Huxley equation that is used to calculate total current? | tot current = (capacitance current) + (K+ current) + (Na+ current) + (leakage current) |
| simulation 5: How does current pulse change the voltage across a membrane, when it is only a plain lipid bilayer? | when the current pulse changes the bare membrane, the voltage rises as a linear ramp |
| simulation 5: How does current pulse change the voltage across a membrane, when leakage channels were added? | voltage initially rose up ramps trajectory then deviated from ramp. The rate of change of the voltage decreases as the voltage rises towards a steady state level. At the end of the current pulse, the voltage exponentially decays to resting pot. |
| simulation 5: How does current pulse change the voltage across a membrane, when vg-Na+ and -K+ channels were added? | there were no noticeable changes until the action potential arose. The voltage then increases at a rate the surpasses the linear ramp for the purely capacitive membrane |
| Simulation 5:The capactive current has four distinct phases. (1) first, one sees the outward current resulting from the brief stimulus current. It retains the square shape of the stimulus because why? | most of this current flows through the membrane's capacity rather than through any channels |
| Simulation 5:The capactive current has four distinct phases. (2) the second phase is a large surge of outward current, reflecting what? | the very high rate of depolarization during the rising phase of the action potential. The inward Na current supplies this outward capacitive current to complete the circuit |
| Simulation 5:The capactive current has four distinct phases. (3) as the action potential approaches its peak, the capacitive current reverses polarity and approaches zero. When does the capacitive current precisely cross zero? | when the action potential reaches its peak, because at this moment the rate of change of the voltage is zero |
| Simulation 5:The capactive current has four distinct phases. (4) throughout the long falling phase of the spike, the capacitive current is inward and now of small amplitude. What does this smaller amplitude reflect? | the much slower repolarization during the falling phase of the action potential due to the competition between the Na and K currents |
| Simulation 6:in this simulation you learned about nernst equation and used it to calculate equilibrium potentials for different ions. You will also look at how the resting potential depends on what? | relative permeabilities (conductances) of Na+ and K+ |
| simulation 6: Glial cells are solely permeable to which ion? | K+ |
| simulation 6: What is K conductance? (give a number) | -77.31mV |
| simulation 6: what is the relationship between [K]o and Ek? | They are directly proportional. As one increases so does the other |
| simulation 6: what is the relationship between [Na]o and Ena? | They are directly proportional. As one increases so does the other |
| simulation 6: if ion concentrations do not change, does equilibrium potentials for those ions change? | no |
| simulation 6: What does ratio between Na and K conductance (ion selectivity) determine? | membrane potential |
| simulation 6: if you could measure the Na and K currents flowing across the membrane at a Na:K ratio of 1:50, what would youobserve? | you would see a small inward Na current attempting to drive Vm towards Ena, and an equal and opposite outwar K current attempting to drive Vm towards Ek. Withthe two currents precisely equal and opposite, Vm rests at a stable value |
| simulation 6: why then is the resting potential so insensitive to the Na concentration when K is 50 times more permeant than Na? | Ena is significantly (+) and Na conductance is small, making it a negligible contribution to determining the resting potential. |
| simulation 7: in this simulation you examined how the action potential and its underlying currents and conductances changes in a uniform patch of membrane. You introduced toxins and observed their effects. And examined the refractory periods | :) |
| simulation 7: what is a "patch" action potential? | a transient, regenerative voltage change that happens in one location. (non-propagating AP) |
| simulation 7: jthe depolarizing ramp at the beginning of the action potential is what? | the charging of the membrane by the pulse of stimulus current |
| simulation 7: what does changing the length or diameter of the patch do to the AP? | it does not alter the AP because even though the surface area of the membrane increased, the membrane's capacity also increased. This balance ensures that the shape of the AP is independent of the area of uniform patch |
| simulation 7: Does the location of the stimulating electrode in the patch matter? | no because the patch is isopotential |
| simulation 7:capacitive current flows onto the membrane during an AP evoked by what? | a brief depolarization |
| simulation 7: under voltage clamp conditions, how is the capacitive current restricted? | restricted to the brief time interval during which the voltage step rises or falls |
| simulation 7: What does TTX and anesthetics do to the AP? | causes the APs rate of rise to slow and its peak to be reduced |
| simulation 7: Na and K currents compete in trying to depolarize and repolarize the membrane.What happens when Na is halved by TTX? | the K conductance retains its normal sensitivity to depolarization |
| simulation 7: when both Na conductance and K conductance are halved by __________, the two currents are evenly matched | lidocaine |
| simulation 7: relative refractory period | allows regeneration of AP due to some Na channels being closed |
| simulation 7: absolute refractory period | no regenerative response because Na channels were stuck open |
Created by:
cmccartney2