Question

1)

Which of the following is/are true for both graded potentials and action potentials?

	a.	Effective for communicating over long distances
	b.	Initiated by transmembrane channel proteins
	c.	Exhibit relative and absolute refractory periods
	d.	both a) and b) are correct, and c) is incorrect
	e.	a), b) and c) are all correct

2)

Which of the following statements about Ion channel activity during the action potential is/are correct?

	a.	At the peak of an action potential, Na+ channel activation gates are open, Na+ channel inactivation gates are closing, and activation gates for K+ channels are opening.
	b.	At resting membrane potential, most voltage-gated Na+ and K+ channels are in the closed configuration.
	c.	During repolarization the activation gates of most voltage-gated K+ and Na+ channels are open.
	d.	both a) and b) are correct, and c) is incorrect
	e.	a), b) and c) are all correct

Answer 1

Answer 1: b. Initiated by transmembrane channel proteins

Explanation:

(a) is not correct because graded potentials travel by passive spread and their amplitudes diminishes with distance. On the other hand, action potentials travel through saltatory conduction and their amplitudes does not diminish with distance. Therfore, Action potentials are effective for communicating over long distances but graded potentials are not.

(b) is correct because both graded potentials and action potentials are initiated by ion channels which are transmembrane channel proteins.

(c) is incorrect because there is no refractory period associated with graded potentials whereas absolute and relative refractory periods are important aspects of action potentials.

Answer 2: d. both a) and b) are correct, and c) is incorrect

Explanation: The voltage-gated Na+ channel has two gates:

• activation gate, which opens when the membrane potential surpasses -55 mV.
• inactivation gate, which closes after a specific period of time  

At rest, the activation gate is closed and the inactivation gate is open. When the threshold is reached, the activation gate opens, allowing Na+ to rush into the cell. At the peak of depolarization, the Na+ inactivation gate closes and activation gates for K+ channels are opening. During repolarization, no more sodium can enter the cell. When the membrane potential passes -55 mV again, the activation gate closes. After that, the inactivation gate re-opens, making the channel ready to start the whole process over again.