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PBD > Resting Membrane Potential and Action Potential > Flashcards

Resting Membrane Potential and Action Potential Flashcards

1
Q

Separation of charges creates ________,

A

A voltage

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2
Q

What is voltage?

A

Electrical pressure or potential, created by the separation of charged ions

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3
Q

What is current?

A

Any net flow of charge. By convention, positive current flows in the direction of positive charges, and is measured in amperes. Ampere = 1 Coulomb per second

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4
Q

What is conductance?

A

A measure of the ease of current flow between two points Measured in siemens. G=1/Resistance

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5
Q

What is Ohm’s law?

A

V=IR V=Voltage I=Current R=Resistance

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6
Q

What is capacitance?

A

A measure of the ability to separate charge. A pure phospholipid bilayer is one of nature’s best capacitors, because its very thin and impermeable to charged ions

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7
Q

The total capacitance of a cell is proportional to the __________ and typically will be on the order of _______.

A

Surface area of its membrane; picoFarads (pF)

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8
Q

What is the difference between passive and active membrane properties?

A

Passive: non-gated static property of membranes that affects current flow. Cells have channel that are always open, allowing certain ions to leak through. This affects the membrane resistance to flow. Tiny changes in membrane potential (4 or 5 mV). Active: Active: non-static properties of membranes that affect current flow. These channels are gated and can be opened or closed given the right conditions. Active + Passive = action potential (change of about 100mV).

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9
Q

What is equilibrium potential?

A

Equilibrium potential of a specific ion is the voltage at which there will be no net movement of the ion through an open conductance.

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10
Q

True or False: Every ion has its own equilibrium potential

A

False Every PERMEANT ion has an equilibrium potential, meaning one for which there is a population of selective ion channels embedded in the membrane

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11
Q

There are two primary driving forces that work together to set the equilibrium potential for an ion. The forces are produced by…

A

1) The chemical gradient 2) The electrical gradient

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12
Q

If a passive (non-selective) pore opens, what happens to the equilibrium potential?

A

Passive (Non-selective) pore opens: equilibrium potential does not change, because there is an equal distribution of ions inside and outside the membrane.

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13
Q

If an active (selective) pore opens, what happens to the equilibrium potential?

A

This creates a voltage across the membrane equal to the equilibrium potential of the ion passing through the channel.

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14
Q

What equation is used to calculate the equilibrium potential for an ion?

A

Nernst equation Eion=[(R*T)/(Zion*F)]*ln(ionin/ionout) R=gas constant Z=charge T=temperature F=faraday constant

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15
Q

At 37 degrees Celsius, RT/F equals…

A

26

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16
Q

For monovalent cation, the Nernst equation can be simplified to be…

A

Eion=60*log[ionin]/[ionout]

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17
Q

The equilibrium potential for an ion is reached when…

A

the driving force for the ELECTRICAL GRADIENT and the driving force for the CHEMICAL GRADIENT are equal and opposite

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18
Q

True or False: Having a membrane potential means the entire inside of the cell is charged with respect to the outside

A

FALSE. The membrane potential is an electric field across the membrane only. Bulk solutions are neutral in charge.

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19
Q

What is resting membrane potential?

A

The voltage across the membrane of a cell (The weighted average of the equilibrium potentials for all permeant ions)

20
Q

What is the weighting factor for resting membrane potential?

A

Permeability.

21
Q

What is the intracellular concentration of potassium? Extracellular?

A

140; 5

22
Q

What is the intracellular concentration of sodium? Extracellular?

A

5-15; 145

23
Q

What is the intracellular concentration of chloride? Extracellular?

A

4-30; 110

24
Q

What is the intracellular concentration of calcium? Extracellular?

A

0.0001; 1-2

25
Q

Voltage across a membrane with permeability >1 ion can be calculated with the ….

A

Goldman equation

26
Q

If the total driving force of Na+ into the cell is high, why is the net flux low?

A

Because Na+ has a low permeability

27
Q

If the driving force of potassium out of the cell is low, why is the net flux high?

A

Potassium has a high permeability

28
Q

The first demonstration of “animal electricity” was observed what year?

A

1790’s

29
Q

Originally, scientists believed that the membrane was only permeable to ________ at rest. This was not true, because it is not the only permeable ion.

A

Potassium

30
Q

It was first proposed that the membrane became so “disorganized” when excited that it would…

A

allow any ion to pass freely through it. Not true

31
Q

How did scientists discover that an action potential was dependent on external Na+ ions?

A

The wire had to be in a medium with sodium ions to cause muscle contraction

32
Q

How did the first accurate measurement of an action potential disprove Bernstein’s general permeability theory of excitation?

A

The voltage doesn’t go from -60 to zero, it goes from -60 to something higher than zero

33
Q

Why is there an overshoot (greater than zero) in action potentials?

A

Because the equilibrium for Na+ is positive

34
Q

At rest: PK+ __ PNa+

At peak pK+ __ PNa+

At recovery PK+ __ PNa+

A

At rest: PK+ >> PNa+

At peak pK+ << PNa+

At recovery PK+ >> PNa+

35
Q

True or False: Threshold voltage does not vary with stimulus amplitude or duration

A

True

36
Q

How can you calculate conductance from Ohm’s law?

A

G=I/(Vm-Eion)

37
Q

What two similarities and two differences did the study of Na+ and K+ conductances under voltage clamps reveal?

A

Two similarities: Both populations of channels open in response to depolarization, both open ore rapidly with greater depolarization

Two differences: Na+ channels have faster activation kinetics at all voltages, During maintained depolarizations Na+ channels inactivate while K+ channels do not

38
Q

Describe the Hodgekin-Huxley model for K+

A

o Each channel has 4 voltage sensitive “gates” called “n-gates”.
o Depolarization opens these n-gates.
o In order for K to start flowing, all 4 n-gates must be open.
o Calculating IK (K current):
IK = (E – EK) * (N * GK * Po)
• N = # of K channels present
• GK = conductance of one channel
• Po = probability that a channel is open

39
Q

Describe the Hodgekin-Huxley model for Na+

A

Each channel has 4 voltage sensitive “gates”
3 m-gates (activation gates)
1 h-gate (deactivation gates)16
o Depolarization:
Open m-gates
Closes h-gates
o M-gates respond faster to changes in V than h-gates.
o There is a brief period in which m-gates open, but h-gate hasn’t closed.
o Brief moment of Na+ conductivity, which takes the A.P. to the overshoot.
o Calculating INa (Na current):
INa = (E – ENa) * (N * GNa * Po)

40
Q

How do you calculate the total current?

A

• Itotal = IK + INa + Ileak

Ileak= -49 mV

41
Q

Describe the 4 phases of an action potential

A

Rest - Set largely by resting conductance to K+ (some other ions involved)

Threshold - the voltage at which the Na+ current exceeds the K+ current, and a regenerative Na+ spike is initiated

Rising phase - initiated by v-gated Na+ conductance. Driven by positive feedback. Terminated Na+ channel inactivation, ENa+, and slow activation of K+ channels

Peak/Overshoot: Would not exceed 0 mV without selective permeability to Na+

Falling phase: Driven by loss of Na+ conductance due to inactivation, and outward flow of K+ due to non-inactivating channels

Undershoot: occurs because EK+ is more negative than the resting membrane potential. With Na+ channels inactivated or closed, Vm will approach EK+ until K+ conductance returns to resting level

42
Q

What are the two main variables that effect the speed of propagation?

A

The axial resistance of the axon (Ra) and the capacitance of the axonal membrane (Cm)

43
Q

As diameter increases, Ra _______ and Cm ______, conduction speed _______

A

Ra gets smaller, Cm gets bigger, conduction speed increases

44
Q

How does wrapping myelin around an axon affect its capacitance?

A

Myelin makes it a less effective capacitor

45
Q

What is saltatory conduction?

A

Action potentials propagate quickly between breaks in the myelin called Nodes of Ranvier. They slow down as they approach the nodes, then they are recharged and pick up speed again

46
Q
A

PBD (7 decks)

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