4. You are recording a neuron, and the cell is at resting membrane potential (-7

Question

4. You are recording a neuron, and the cell is at resting membrane potential (-70mV) when you inject a small amount of current eliciting a 5 mV increase that fades. You inject double the amount of current and elicit a 10 mV increase that fades. You inject 3 times the original amount of current, and now you see an action potential as such: +40 70 Rosting membrane potentia Stimulus Sbmulus 1& 2 Time (ms) First, what is the approximate threshold of this neuron? If you inject a current that is four times your original, what do you expect to see happen to the action potential? What happens to the action potential when you apply the following drugs individually to the recording chamber (You may draw simple diagrams to help illustrate your point): A. tetrodotoxin (blocks voltage gated Na+ channels) B. TEA (blocks voltage gated K+ channels)

Explanation / Answer

The threshold is about 15mV since an action potential was generated at 3 times the original (5mV). nothing would happen if you would inject a current four times the original because an action potential is an all or none potential once the threshold is reached an action potential will generated of a particular amplitude independent of the current you apply over the threshold range.

A. Sodium channels bring in the sodium ions which bring in the threshold current to the neuron to generate an action potential. if a drug is added that block these channels then the action potential won't be generated.

B. Voltage gate potassium channels bring the potassium ions inside and help repolarize the membrane of the neuron. If these are blocked the membrane remains repolarized and doesn't reach a repolarized and eventually a resting stage.

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