Question 1 (5 points) Which of the following best describes how sodium and potas

Question

Question 1 (5 points) Which of the following best describes how sodium and potassium are involved in changing potentials along an axon? A channel for each ion is activated by a different potential difference across the membrane. Both sodium and potassium enter the cell rapidly when upon arrival of an action potential, greatly increasing the positive charge inside the cell Sodium's positive charge causes a positive charge in the cell when its ion channel is opened and potassium's negative charge helps to restore the cell to its resting potential. With the arrival of the action potential, the cell moves sodium into the cell against its concentration gradient through co-transport with potassium.

Explanation / Answer

1) a. A channel for e h ion is activated by a different potential difference across the membrane.

The sodium channels open first while the potassium channels open a little later when the membrans potential is a little less negative (caused by the influx of sodium).

Not (b) because sodium moves into the cell while potassium moves out of the cell.

Not (c) because sodium and potassium are both positively charged.

Not (d) because both sodium and potassium move down the gradient when their channels open - Sodium concentrations are high outside while those of potassium are high inside the cell.

2) b. Without insulation, nerve impulses would be greatly slowed down. However with additional ion channels in demyelinated areas, conduction speed could be restored to normal.

Myelination aids faster conductance of impulse. To compensate for it post-demyelination, number of ion channels would increase by adding ion channels to the open demyelinated areas.

Not (a) because nodes of Ranvier are sites where myelin sheath is absent it's cannot be shrunk or reduced by adding ion channels in its place.

Not (c) because impulse can propagate between ion channels with or with myelin sheath being present.

Not (d) because strength of the nerve impulse depends on the strength of initial stimulation, and the concentration of ions and not the presence of myelin sheath.

4) b. The membrane potential is -30mV before treatment and -10mV after treatment.

Sodium is a positively charged ion . So, when the drug treatment is given, the sodium ion channels open causing an influx of sodium making the membrane potential less negative.

Not (a) and (c) because -50 and -60 are more negative potential values than -30.

Not (d) because stimulation of sodium channels would open them causing sodium to inflow down the gradient.

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