BMS-325-Exam-2

Question 1

T/F: The permeability of the membrane to different ions is one of the factors that determines the Resting Membrane Potential.

Answer 1

True.
Flow of ions into the membrane determines how many charges are inside and outside which is how the membrane potential is built.

Question 2

T/F: Ionic currents literally mean flow of ions, it is directly related to ion conductance which is the electrical term for permeability or ease of flow.

Answer 2

True.
The equation shows us that the quantity of ionic flow or Ionic current is dependent on the ease of the ion flow G_ion and the electrochemical driving force which can be expressed as the difference between membrane potential and E_ion.

Question 3

T/F: When a neuron is hyperpolarized, this means that is new membrane potential is lower or more negative than 0mV.

Answer 3

False.
The reference point is the resting membrane potential, not 0mV.

Question 4

T/F: The ionic current observed in the early phase of the action potential and late phase of the action potential are due to two different ion fluxes, namely Na⁺ then K^+.

Answer 4

True.

Question 5

T/F: Tetradotoxin is a poison that blocks Potassium voltage gated channels

Answer 5

False.
Tetradotoxin (TTX) blocks Sodium (Na_v) channels.

Question 6

T/F: TEA (Tetraethylammonium) blocks Sodium channels.

Answer 6

False.
TEA (Tetraethylammonium) blocks Potassium (K_v) channels.

Question 7

A squid giant axon is depolarized to initiate an Action Potential. During this action potential the following things happen (chose the best option):
A.) K_v channels open immediately then Na_V.
B.) Na_V open immediately after depolarization then quickly inactivate.
C.) K⁺ open slowly after depolarization and stay open until V_m is at E_K.
D.) All of the above.
E.) B and C.

Answer 7

E.) B and C.
K_v channels do not open immediately.

Question 8

One of the following components is not part of the voltage clamp setup:
A.) An electromagnet
B.) The recording electrode.
C.) The current passing electrode.
D.) The refrence electrode.

Answer 8

A.) Electromagnets are not part of the voltage clamp setup; however, recording, current passing, and reference electrodes are.

Question 9

When a giant axon is depolarized to +52 mV with E_K=-85mV E_Na=+52mV the reason why there is no outgoing Na⁺ current is:
A.) The Na_v gated channels are not open.
B.) There is no ion flux, as V_m and E_Na are equal.
C.) At +52mV all the Na⁺ ions are bound to the channels.
D.) At +52 K⁺ out and Na⁺ ion influx are the same.

Answer 9

B.) Because V_m and E_Na have the same potential, there is no ion flux.
….
A.) During depolarization, Na_v’s channels are fully open, so not A.
C.) Doesn’t make any sense.
D.) Ion flux are not the same when K⁺ = +52mV, and Na⁺ = +52mV.

Question 10

The voltage clamp setup clamps the membrane potential of the axon by:
A.) Physically clamping the axon.
B.) Injecting charges (electrons) into the axons, compensating for ion fluxes happening at the membrane.
C.) Injecting Na⁺ ions into the axon.
D.) Producing an electromagnetic field that scrambles the capacitance of the membrane.

Answer 10

B.) Injecting a current into the axon allows simulation of ion fluxes occurring at the membrane.
….
A.) Clamping the axon doesn’t do anything. Clamping is a general term used for clamping the voltage level, not physically clamping the axon.
C.) Injecting ions into the axon is not the same as an electrical flow.
D.) Producing EMF will only carry current across a membrane, not scramble it.

Question 11

Where is the recording electrode in the patch clamp setup?
A.) In the axon.
B.) On the axon membrane.
C.) Outside the axon.
D.) None of the above.

Answer 11

A.) In the axon.
….
B.) Current on the outside of the axon doesn’t help simulate anything.
C.) Outside the axon means that current wouldn’t create an action potential, and thus, doesn’t make any sense.

Question 12

What is the role of the current passing electrode in the voltage clam setup?
A.) Record the membrane potential.
B.) Inject current into the axon to clamp the membrane potential.
C.) Inject current into the axon and record how much current is needed to clamp the membrane potential.
D.) All of the above.
E.) None of the above.

Answer 12

C.) This is where current is injected, and the amount of current needed to clamp the membrane is recorded.
Inject current to make V_m = V_c.
….
A.) This is the recording electrode (inside the axon).

Question 13

T/F: The current recorded is opposite to the ion flux happening at the plasma membrane.

Answer 13

True.
The current recorded during ion flux at the plasma membrane is typically opposite in direction to the actual movement of ions. This is because current represents the movement of positive charge, and the convention is that positive current corresponds to the flow of positive ions out of the cell, or negative ions into the cell.

Question 14

T/F: The capacitive current corresponds to the number of charges V_m=Q/C injected to bring V_m=V_c.

Answer 14

True.
Q = number of charges, and thus injecting current (electrical charges) makes V_m=V_c.

Question 15

T/F: The capacitive current is smaller the larger the axon volume is.

Answer 15

False.
A larger axon will require more current to function when compared to a smaller axon’s current.

Question 16

T/F: During voltage clamp, the current I_m is always the same, but the V_m changes.

Answer 16

False.
You clamp the membrane to set the V_m to a static value; however, I_m (current) changes.

Question 17

T/F: Voltage Clamp is an electrical recording method for electrophysiology.

Answer 17

True.

Question 18

T/F: Voltage Clamps the V_m to a certain value compensating for ionic current across the axon membrane by injecting current.

Answer 18

True.

Question 19

T/F: How much current is injected reveals what is going on with the flux of ions.

Answer 19

True.

Question 20

T/F: Hodgkin and Huxley used voltage clamping to reveal that there were two voltage dependent changes in ion flow during an action potential.

Answer 20

True.
K⁺ and Na⁺.

Question 21

T/F: Na⁺ and K⁺ voltage-dependent channels are essential for the action potential in the giant squid axon.

Answer 21

True.

Question 22

T/F: The conductance and permeability of the plasma membrane are the same.

Answer 22

False.
Conductance is the electrical measurement of the ability to flow. (Reverse of the resistance).

Question 23

T/F: The conductance of the membrane is the opposite of resistance.

Answer 23

True.

Question 24

T/F: Ionic currents and electric currents are the same.

Answer 24

False.
Ionic and electrical currents are not the same, but they work together.

Question 25

T/F: Which voltage-gated channel opens first in an action potential?
A.) Na_v
B.) K_v

Answer 25

A.) Na_v
….
K_v has a delayed response (delayed rectifier).

Question 26

What is the difference in the gating mechanism between Na_v and K_v?
A.) Na_v channels have two gates.
B.) K_v have a delayed activation.
C.) Na_v channels have a delayed inactivation gate.
D.) All of the above.

Answer 26

D.) All of the above.

Question 27

T/F: Hodgkin and Huxley showed that currents that flow during depolarization of the membrane are due to three different time-dependent and voltage-sensitive processes:
1.) Activation of Na⁺ conductance.
2.) Activation of K⁺ conductance.
3.) Inactivation of Na⁺ conductance.

Answer 27

True.

Question 28

T/F: Na_v are made of four separate subunits?

Answer 28

False.
Na_v are made up four separate domains, all part of one α-subunit.

Question 29

T/F: All Na_vs have the same voltage and kinetics.

Answer 29

False.
Most gates have different voltages and kinetics, especially depending on where they are located in the body.

Question 30

T/F: Na_vs are only found in the brain.

Answer 30

False.

Question 31

T/F: K_v and Na_v are both heterotetramers.

Answer 31

False.

Question 32

T/F: The diversity of K_vs is higher than that of Na_vs.

Answer 32

True.
There are far more K_vs than Na_vs.

Question 33

T/F: K_v have a larger portion of their structure inside the cell compared to Na_v channels.

Answer 33

True.

Question 34

What are the four main types of voltage-gated channels?

Answer 34

Na⁺, K⁺, Cl^-, and Ca²⁺.

Question 35

T/F: K_v channels are the most diverse followed by Ca_v and Na_v.

Answer 35

True.

Question 36

T/F: K_v channels have four subunits with six transmembrane helices that make the pore.

Answer 36

True.

Question 37

T/F: Na_v and Ca_v have one main alpha subunit with four subdomains that make the pore.

Answer 37

True.

Question 38

T/F: Cl^- channels are made out of two subunits with one pore each.

Answer 38

True.

Question 39

T/F: The voltage sensitivity and kinetics of all channels change for each combination of protein subunit or genes expressed.

Answer 39

True.

Question 40

T/F: All voltage-gated channels are expressed in many different tissues, neurons (axons and dendrites), and muscle tissue.

Answer 40

True.

Question 41

T/F: Diseases associated with mutations are called channelopathies.

Answer 41

True.

Question 42

When Na_v open the flow of the ions is determined by:
A.) E_Na.
B.) V_m.
C.) A and B.
D.) None of the above.

Answer 42

C.) A and B.

Question 43

T/F: If the concentration of Na⁺ outside of the neuron changes, this does not affect the shape of the action potential.

Answer 43

False.
Na⁺ concentration changes impacts the resting membrane potential, GHK, changes the way ions flux, and ultimately changes the action potential shape.

Question 44

Different Na_v isoforms change the shape of the action potential because:
A.) Their activation and inactivation gates are different.
B.) The number of Na⁺ they let through is different.
C.) They affect the E_Na differently.
D.) All of the above.
E.) A and B.

Answer 44

E.) A and B.
Both A and B are referring to conductance, and therefore are both correct.
….
C.) Equilibrium constant doesn’t change with isoforms.

Question 45

T/F: The density of Na_v at the Axon Initial Segment (AIS) is the only determinant of action potential initiation.

Answer 45

False.
There are many determinants for action potential initiation, including:
Na_v channel type and gate.
Na_v density at Axon Initial Segment (AIS).
K_leak of the membrane at AIS.
Membrane resistance.
Temperature.

Question 46

T/F: The density of K_leak at the Axoin Initial Segment (AIS) increases the threshold of action potential initiation.

Answer 46

True.
More ion flux leaking out increases the threshold of action potential.

Question 47

One of these sentences below is not a factor in action potential initiation at the Axon Initial Segment (AIS):
A.) Na_v density.
B.) K_leak density.
C.) Type of Na_v gate.
D.) Type of K_v gate.
E.) Membrane resistance.

Answer 47

D.) Type of K_v gate.
K_v is voltage-sensitive and is a delayed initiation.
All others have direct impact on the AIS action potential.

Question 48

T/F: Action potential shape is primarily determined by the properties of Na_v and K_v

Answer 48

True.

Question 49

T/F: Action potential initiation requires V_m>Na_v voltage gate (around -20mV).

Answer 49

True.

Question 50

T/F: The action potential threshold at the Axon Initial Segment (AIS) depends on Na_v type, Na_v density, and membrane leak.

Answer 50

True.

Question 51

T/F: Temporal and spatial summation of synaptic potentials lead to large enough changes of V_m for action potential initiation.

Answer 51

True.

Question 52

T/F: Sequential action potential initiation is constrained by the refractory period of the Na_v inactivation (absolute refractory period), and K_v opening (relative refractory period.

Answer 52

True.