Membrane Potential and Ion Channels Flashcards Preview

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Flashcards in Membrane Potential and Ion Channels Deck (35)
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1
Q

Synaptic Transduction

A
2
Q

Excitability

A

Excitability refers to the ability of a cell to generate action potentials, which means a transient depolarization and repolarization of the cell’s membrane potential.

3
Q

Free Energy of Transport Equation

A
4
Q

Cellular vs Blood Ions

A
5
Q

The asymmetry in Na+ and K+ concentrations in the blood and cytoplasm is due to the activity of. . .

A

Na+ / K+ ATPase:

Transports 3 Na+ ions out of the cell and 2 K+ into the cell.

6
Q

The asymmetry in Ca2+ concentration between the SR and cytoplasm is due to the activity of. . .

A

SERCA pumps

7
Q

Balance of Electrical and Concentration Gradients Across a Selectively Permeable Membrane

A
8
Q

You set up a selectively permeable membrane, only permeable to potassium, and allow potassium to diffuse. If you measured the potassium concentrations in the two compartments after opening the channels, what would the difference be?

A

Almost nothing! It would hardly be detectable. Note that it only takes a limited number of potassium ions to move across the membrane to develop a difference in voltage.

9
Q

Resting voltage for a selectively potassium permeable membrane

A
10
Q

Resting voltage for a selectively sodium permeable membrane

A
11
Q

Nernst Potential equation for ion transport

A

The Nernst potential for any given ionic species is the membrane potential at which the ionic species is in equilibrium; i.e., there is no net movement of the ion across the membrane. Therefore, the Nernst potential for an ion is referred to as the equilibrium potential (Veq.) for that ion.

REMEMBER: For ion transport, the negative sign is removed from the Nernst equation. Bear in mind whether your ion is positive or negative!!!!!! That will determine the sign of the z variable. It is assumed to be POSITIVE as a default, as in concordance with the standard assumption of positive current flow in physics.

12
Q

By convention, membrane potential is typically descirbed as. . .

A

The inside to outside potential

In other words, always use [X]out/[X]in

13
Q

Goldman equation

A

Where Px is the permeability of ion x.

Note that this is simply a summation of Nernst potentials for the ions, and that whether it is in/out or out/in depends on the ion’s charge and therefore sign.

14
Q

A sudden change in the extracellular potassium concentration can cause life-threatening arrhythmias and may lead to a complete loss of neuronal excitability. Use the Goldman Equation and the data given regarding the intracellular and extracellular concentrations of each ion as well as their membrane permeability to calculate the transmembrane potential as the extracellular concentration of potassium is raised from 4.5 to 100 mM in increments of 5 mM; contrast this to a similar calculation on raising the extracellular sodium concentration from 135 mM to 235 mM in increments of 5 mM.

A
15
Q

RT/F

A

0.02699

16
Q

In most cells at rest, ___ channels are open, but ___ channels are not.

A

In most cells at rest, potassium channels are open, but sodium channels are not.

17
Q

_____ channels that set the resting membrane potential.

A

Potassium channels that set the resting membrane potential.

These channels are open at rest and are not voltage-gated. They set the resting membrane potential near the Nernst potential for potassium (typically -60-80 mV).

18
Q

_____ channels initiate an action potential.

A

Ligand-gated sodium channels initiate an action potential.

19
Q

These channels open in response to depolarization of the membrane

A

Voltage-gated sodium channels: These channels open in response to depolarization and have a unique feature of inactivating themselves after a short period. These channels are essential for propagating an action potential.

Voltage-gated potassium channels: These channels also open in response to depolarization, but more slowly than the sodium channels. These channels help restore the membrane potential back to the resting potential. Like sodium channels, they also inactivate themselves over time.

Voltage-gated calcium channels: (In muscle) These channels allow calcium influx from either the outside of the cell or the sarcoplasmic reticulum in response to the action potential (depolarization). These channels also inactivate themselves over time.

20
Q

Depolarization

A

When the membrane potential is moving closer to 0.

21
Q

Action potential diagram

A

VT: the threshold voltage that triggers opening of the voltage gated sodium channel

VNa: the Nernst potential for sodium

VK: the Nernst potential for potassium

22
Q

Sodium and potassium channel conductances during action potential

A

The membrane repolarizes when gK is greater than gNa

Note that this diagram only shows the conductance of the voltage gated channels; it does not show the conductance of the potassium channels that are open in the membrane at rest.

23
Q

Voltage gated sodium channel mechanism

A

At resting potential in the membrane, the channel is closed. Upon depolarization to the threshold voltage, the channel opens (1 below). While the membrane is depolarized, the channel then undergoes inactivation (2 below). This is a different conformation than the initial closed state (note bottom gate is closed). To open again, the channel has to cycle back to the resting state (3 below).

Note the critical importance of the inactivation step. If the channel did not inactivate, the membrane would remain permeable to sodium, and the cell would remain depolarized.

24
Q

Cholinergic Synapse Diagram

A
25
Q

Muscarinic receptors are ____. Nicotinic receptors are ____.

A

Muscarinic receptors are metabotropic. Nicotinic receptors are ionotropic.

26
Q

Nicotinic Receptor Structure

A
27
Q

Nicotinic Receptor Gating

A

Note that channel opening and closing are much slower events than binding of ACh to the receptor.

28
Q

Neuromuscular Junction

A
29
Q

Quantal Release of Acetylcholine Triggering Action Potentials

A

Q or MEPP (miniature end-plate potential) is a small depolarization event caused by the release of a small quantum of acetylcholine (degranulation). Multiple MEPPs concurrently or in quick succession may generate an action potential.

30
Q

Excitation-Contraction Coupling

A
31
Q

Lidocaine

A

Na+ Channel antagonist

Prevents propagation of an action potential, but does not change the resting membrane potential.

32
Q

Nerve voltage-gated sodium channels are ____ while the heart voltage-gated sodium channel is ____.

A

Nerve voltage-gated sodium channels are Nav 1.7 and 1.8 while the heart voltage-gated sodium channel is Nav 1.5.

33
Q

Fasciculations

A

Non-coordinated muscle contractions caused by chemical interaction with contraction machinery.

Initial response to a depolarizing neuromuscular blocker

34
Q

Succinylcholine

A

Succinylcholine blocks the transmission of the signal WITHIN THE MUSCLE FIBER.

Think about the muscle ADJACENT TO and DOWNSTREAM OF the cell of the neuromuscular endplate.

35
Q

Plasma pseudocholinesterase

A

The enzyme that degrades succinylcholine as it diffuses out into the blood.