You are characterizing the firing rate of a neuron by continuously injecting dif
ID: 132534 • Letter: Y
Question
You are characterizing the firing rate of a neuron by continuously injecting different amounts of current into the cell. You plot the results:
A) From this data, what would you conclude is the duration of the absolute refractory period of the neuron? Briefly explain your thinking.
B) This neuron is a pain-sensing neuron ("nociceptor)" from a person with a disorder that makes them hypersensitive to pain. You believe the condition is caused by the neuron firing at a higher than the normal rate when stimulated. Come up with an idea for a drug that would act on a voltage gated ion channel to help this person remember we want to keep person's ability to feel pain but reduce the pain they feel so the drug should reduce not eliminate the firing rate. Explain how your drug would work and describe (or insert sketch) of how the shape of the action potential would change after adding the drug
Firing Rate vs. Simulating Current 550 500 450 400 N350 C 300 250 200 150 100 50 50 100 150 200 250 300 350 400 Injected Current (pA)Explanation / Answer
A. Upto a current of 75 pA, is the absolute refractory period where the fringe frequency rate is 0. Generally they are 1-2 ms. Absolute refractory period is the timepoint during which a second action potential cannot be initiated, even if the stimulus is strong enough. It needs to clear a certain value to generate action potentials.
B. Most of Na+, K+,Ca2+ and Cl- channels are the ones that are gated by voltage whereas some of the channels like ryanodine receptors are voltage insensitive. The disorder is called hyperalgesia which is due to the damage caused to nociceptors. Lidocaine at a low concentration can block voltage gated sodium channels and the action potential that will be fired will be considerably lower as the sodium channels are blocked. At a higher concentration, lidcoaine might numb the tissue completely blocking the voltage gated channels preventing the action potential propagation. Thus at an appropriate concentration of the drug, an inidividual will feel the pain but to a lesser extent.
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