Chapter 4

Question 1

The rising phase is characterized by:

Answer 1

A rapid depolarization of the membrane. This change in membrane potential continues until the membrane potential reaches a peak of about 40 mV

Question 2

What is the overshoot?

Answer 2

The part of the action potential where the inside of the neuron is positively charged with respect to the outside

Question 3

What is the falling phase?

Answer 3

a rapid repolarization until the membrane is actually more negative than the resting potential

Question 4

What is the undershoot or after-hyperpolarization?

Answer 4

The last part of the falling phase when the membrane potential is more negative than the resting potential

Question 5

What is threshold?

Answer 5

The critical level of depolarization that must be crossed in order to trigger an action potential

Question 6

Graph of an action potential:

Answer 6

Question 7

What is the absolute refractory peroid?

Answer 7

The (about) 1msec during which it is impossible to initiate another action potential after one is initiated

Question 8

What is the relative refractory period?

Answer 8

The several milliseconds after the absolute refractory period during which it is relatively difficult to initiate another action potential

Question 9

Depolarization of the cell during the action potential is caused by ________________ and repolarization is caused by ____________

Answer 9

The influx of sodium ions across the membrane,

The efflux of potassium ions

Question 10

I_K=g_K (V_m-E_K)

I_ion=g_ion(V_m-E_ion)

Answer 10

Where:

I_ion is the electric current of the ion in question

g_ion is the electrical conductance of the ion in question

Question 11

Graph of the action potential WRT sodium and potassium channels:

Answer 11

Question 12

What is a voltage-gated sodium channel?

Answer 12

The protein that forms a pore in the membrane that is highly selective to Na⁺ ions. The pore is opened and closed by changes in the electrical potential of the membrane

Question 13

What is the threshold for voltage-gated sodium channels?

Answer 13

-40 mV

Question 14

What is a channelopathy?

Answer 14

A human genetic disease caused by alterations in the structure and function of ion channels

Question 15

Threshold:

Answer 15

The membrane potential at which enough voltage-gated sodium channels open so that the relative ionic permeability of the membrane favors sodium over potassium

Question 16

Rising Phase:

Answer 16

When the inside of the membrane has a negative electrical potential, there is a large driving force on sodium ions. Therefore, sodium ions rush into the cell through teh open sodium channels, causing the membrane to rapidly depolarize

Question 17

Overshoot:

Answer 17

Because the reative permeability o the membrane greatly favors sodium, teh membrane potential goes to a value close to E_Na, which is greater than 0 mV

Question 18

Falling Phase:

Answer 18

The behavior of two types of channel contributes to the falling phase. First, the voltage-gated sodium channels inactivate. Second, the voltage-gated potassium channels finally open (triggered to do so 1msec earlier by the depolarization of the membrane). There is a great driving force on potassium ions when the membrane is strongly depolarized. Therefore, potassium ions rush out of teh cell through the open channels, causing the membrane potential to become negative again.

Question 19

Undershoot:

Answer 19

The open voltage-gated potassium channels add to teh resting potassium membrane permeability. Because there is very little sodium permeability, the membrane potential goes toward E_K, causing a hyper-polarization relative to teh resting membrane potential until the voltage-gated potassium channels close again

Question 20

Absolute refractory period:

Answer 20

Sodium channels inactivate when the membrane becomes strongly depolarized. They cannot be activated again, and another action potential cannot be generated, until the membrane potential goes sufficiently negative to deinactivate the channels

Question 21

Relative refractory period:

Answer 21

The membrane potential stays hyperpolarized until teh voltage-gated potassium channels close. Therefore, more depolarizing current is required to bring the membrane potential to threshold