Question 1

Repolarization of the nerve during the action potential is caused mainly by

Accepted Answer

Repolarization of the nerve during the action potential is primarily due to the inactivation of the Na+ channels, which stops the influx of Na+ ions, and the simultaneous opening of K+ channels, allowing K+ to exit the cell. This restores the negative internal membrane potential.

Question 2

Opening of the Na+ activation gates in motor neurons is caused by

Accepted Answer

The opening of Na+ activation gates in motor neurons is primarily triggered by the depolarization of the membrane to a threshold level, typically around -50 mV. This depolarization causes the gates to open, allowing Na+ ions to flow into the neuron, further depolarizing it and propagating the action potential.

Question 3

The “overshoot” of the action potential means

Accepted Answer

The "overshoot" of the action potential refers to the phase where the membrane potential becomes positive, exceeding 0 mV, due to the influx of Na+ ions.

Question 4

A cell has a resting membrane potential of -70 mV and E_Na = + 60 mV and E_K = - 90 mV. If g_Na >0 in this cell,

Accepted Answer

The answer of A cell has a resting membrane potential...

Question 5

In most cells, Increasing g_K would cause

Accepted Answer

Increasing g_K (potassium conductance) typically leads to hyperpolarization due to increased I_K (potassium current), as more potassium ions leave the cell, making the inside more negative.

Question 6

Closing of the K⁺ at the end of the action potential requires

Accepted Answer

The closing of ion channels at the end of an action potential typically requires both repolarization, which is the process of the membrane potential returning to its resting state, and time, as these channels often have time-dependent properties.

Question 7

Opening of the inactivation gate of the Na channel

Accepted Answer

The inactivation gate of the Na channel closes (or inactivates) after the membrane has depolarized and the action potential has peaked, leading into the repolarization phase. This process occurs after the membrane has been depolarized, not during the upstroke of the action potential or its initiation. Tetrodotoxin blocks the pore of the Na channel, not specifically the inactivation gate, and TEA is known to block K channels, not Na channels.

Question 8

The E_m for a cell is -70 mV and E_Clis -80 mV. Increasing g_Cl should increase

Accepted Answer

Increasing gCl (conductance for Cl-) would increase the inward flux of Cl- because Cl- ions would move from a higher concentration outside the cell to a lower concentration inside, given the cell's resting membrane potential is -70 mV and ECl is -80 mV. This movement of negatively charged ions into the cell would result in an outward current that hyperpolarizes the cell, making the inside more negative.

Question 9

At rest, the Na channel

Accepted Answer

At rest, the activation gates of sodium (Na) channels are closed to prevent the influx of Na+ ions, while the inactivation gates are open, indicating that the channel could be activated if the membrane potential changes. This state ensures that the neuron remains at its resting potential until a stimulus arrives.

Question 10

In the Hodgkin-Huxley explanation of the action potential, activation gates

Accepted Answer

Activation gates are present on both sodium (Na+) and potassium (K+) channels, but the kinetics of Na+ channel activation are faster than those of K+ channels. This difference in kinetics is crucial for the sequential phases of the action potential.

Question 11

Depolarization refers to

Accepted Answer

Making the membrane potential less polarized - typically making it less negative

Question 12

“Latency” refers to the

Accepted Answer

Latency refers to the delay between the application of a stimulus and the initiation of the action potential. This period is the time it takes for the stimulus to bring the membrane potential to the threshold level, initiating the action potential.

Question 13

The first step in the nerve action potential from rest is

Accepted Answer

The first step in the nerve action potential from rest is the opening of the fast sodium (Na+) activation gates, allowing Na+ ions to rush into the neuron, which initiates depolarization.

Question 14

The time after an excitation during which the cell can produce another action potential, but it requires a larger than normal stimulus, is called the

Accepted Answer

The relative refractory period is the phase following the absolute refractory period during which a neuron can be stimulated to fire again but requires a stronger than usual stimulus. This is due to the fact that some voltage-gated sodium channels are still in the process of resetting and the membrane is closer to its resting potential, but not fully there.

Question 15

The inability of neurons to generate only a part of an action potential is called

Accepted Answer

The all-or-none law states that a neuron either does not respond at all or it responds completely by generating a full action potential. This principle explains why neurons cannot generate only a part of an action potential.

Question 16

In most cells, Increasing g_Na would cause

Accepted Answer

Increasing g_Na (conductance for sodium ions) would lead to an increase in I_Na (sodium ion current), causing more sodium ions to enter the cell. This influx of positively charged ions would make the inside of the cell more positive, leading to depolarization.

Question 17

Suppose that after an action potential we clam p the membrane potential at -50 mV and don’t let it completely repolarize. We find that we cannot elicit an action potential. This is called a depolarization block. What causes it?

Accepted Answer

The answer of Suppose that after an action potential we...

Question 18

The time after an excitation during which the cell cannot produce another action potential is called the

Accepted Answer

The absolute refractory period is the time after an excitation during which a cell cannot produce another action potential, regardless of the strength of the stimulus. This is due to the inactivation of sodium channels, which are necessary for the initiation of an action potential.

Quiz 18: The Action Potential