2. Investigators learned a great deal about how different ions contribute to the

Question

2. Investigators learned a great deal about how different ions contribute to the generation of an action potential by studying axons isolated from the squid. The set of curves shown in the figure below represent action potentials that are generated under three different conditions. In the first curve, which peaks at +40 mV, the ion concentrations inside and outside the isolated axon are similar to what they would be inside and outside a normal neuron. Which of the following treatments would be most likely to produce the other two curves in this figure? 40 -40 time (msec) a. The medium inside the axon contains decreasing concentrations of Ca+. b. The medium inside the axon contains decreasing concentrations of Na. c. The medium outside the axon contains decreasing concentrations of K. d. The medium outside the axon contains decreasing concentrations of Na". e. The medium outside the axon contains increasing concentrations of Na.

Explanation / Answer

d) the medium outside the axon contains decreasing concentrations of Na+

When neuron is at rest there is high concentration of sodium ions outside of cell compared to the concentration inside because of concentration gradient the sodium potassium pump uses ATP to diffuse ions across the membranes and gives resting potential of -70mV.Whern impulse is received by neuron the sodium ions gets open and move inside of cell causing change in the action potential to positive inside of neuron called as depolarization. Again due to repolarization the potassium channels open and potassium ions move out of cell creating more negative charge inside the cell. Potassium ions gain get back into cell by diffusion which can be seen by straight line in graph.

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