Exam 7: Ionic Basis of the Action Potential

You are recording from a neuron under voltage clamp to evaluate whether a new chemical "achematoxin" has any effect on the nervous system. You step the command voltage to +15 mV and find that there is a capacitative current and a robust, delayed late current. What effect, if any, do you suspect achematoxin has on neurons? Explain your answer.

You are performing a voltage clamp experiment in which the neuron's resting potential is -70 mV. When you change the command voltage to + 40 mV, what is the first current that you observe?

In a voltage clamp experiment, you observe that the magnitude of the sodium current decreases when the membrane potential is stepped between +10 and +50 mV. Why?

What is the source of the gating currents?

In a voltage clamp experiment, you observe that the magnitude of the sodium current increases when the membrane potential is stepped between -45 and +10 mV. Why?

Name and describe the three distinct currents that occur following the depolarization of the membrane in a voltage clamp experiment.

Identify and describe the molecular mechanism responsible for sodium channel activation.

Describe the "gating currents" and their physiological source.

In the rotational model of sodium channel activation, what happens when the membrane is depolarized?

In a voltage clamp, which of the following is measured?

Describe the molecular mechanism of sodium channel inactivation, including experimental evidence supporting this mechanism.

Which of the following depends on the flow of potassium ions across the membrane?

The use of choline instead of sodium in the extracellular solution allowed Hodgkin and Huxley to eliminate which of the following from their experiments?

What ion is responsible for the outward current seen in a voltage clamp experiment where the voltage is set to +25 mV?

What is the afterhyperpolarizing potential (AHP), and what is the ionic basis for it?

Compare the time course of individual sodium channel opening and sodium current in the whole cell following membrane depolarization, and explain any differences between them.

You perform a series of voltage-clamp experiments with 2 mM extracellular calcium, 0.2 mM extracellular calcium and 0 mM extracellular calcium. You notice that the potassium current increases with each step. What is the origin of this increase?

What does the voltage clamp experiment measure?

When is a potassium channel most likely to open following a depolarizing stimulus in the neuron?

In a voltage clamp experiment, this current is observed immediately after a voltage step and varies linearly with the size of the voltage step.