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PHYSIOLOGY > ME01 - Membrane Electrophysiology > Flashcards

ME01 - Membrane Electrophysiology Flashcards

1
Q

Characteristics of Ion Channels

A

Ion Channel Selectivity
Ion Channel Gating
Conductance of Ion Channel

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2
Q

Ion channels permit the passage of some ions, but not other

A

Ion Channel Selectivity

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3
Q

Ion Channel Selectivity is based on:

A

Channel size
Distribution of charges that line it
Size and charge of ions
How much water the ion attracts and holds around it

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4
Q

Ion channels are either GATED or NON-GATED

A

Ion Channel Gating

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5
Q

What are Gated ion channels and it’s types

A

Gated ion channels have gates that can open or close the channel
Voltage-gated - gates are controlled by voltage (difference in membrane potential)
Ligand-gated - open or closed by hormones, second messengers or neurotransmitters

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6
Q

Ion channels that are always open

Also called as leakage channels

A

Non-Gated Ion Channels

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7
Q

Conductance of Ion Channels depend on ______

A

If the channel is OPEN

The higher the probability that a channel is open, the higher the conductance or permeability

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8
Q

Location of ION CHANNELS

A

Non-Gated: Cell membrane on dendrites, Cell Body and Axon
Ligand-Gated: dendrites, cell body
Voltage-Gated: Axon hillock, unmyelinated axons, along the nodes of Ranvier in myelinated axons

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9
Q

Functions of ION CHANNELS

A

Non-Gated : RMP
Ligand-Gated: Synaptic potentials (incoming signals to neurons)
Voltage-Gated: Generation and Propagation of action potential (outgoing signals from neurons)

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10
Q

Types of Membrane Potentials

A

Diffusion Potential

Equilibrium Potential

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11
Q

Potential difference generated across a membrane because of a concentration difference of an ion

A

DIFFUSION POTENTIAL

Can be generated only if the membrane is permeable to the ion

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12
Q

Factors related to the Diffusion Potential
Size
Sign

A

Size depends on the size of the concentration gradient

Sign depends on whether the diffusing ion is positively or negatively charged

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13
Q

Diffusion Potential do not result in changes in concentration of the diffusing ions

A

TRUE.

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14
Q

Diffusion potential that exactly balances (opposes) the tendency for diffusion caused by a concentration difference

A

Equilibrium Potential

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15
Q

Chemical and Electrical Driving forces that act on an ion are equal and opposite
No net diffusion of the ion occurs

A

Electrochemical Equilibrium

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16
Q

In the presence of a nondiffusable ion, diffusable ions distribute themselves so that at equilibrium their concentration ratios are equal
For any pair of cation/anion

A

Gibbs-Donnan Equilibrium

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17
Q

Formula for Gibbs-Donnan Equilibrium

A

[K+]in x [Cl-]in = [K+]out x [Cl-]out

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18
Q

Implications and Consequence of Gibbs-Donnan Equilibrium

A

(1) Presence of charged proteins in cells, there are more osmotically active particles in cells than in IF
C: Animal cells have flexible walls; Osmosis make cells swell and rupture; Prevented by Na/K ATPase

(2) At equilibrium, distribution of ions across membrane is assymetric
C: Electrical potential difference exists across membrane (MP)
Magnitude can be determined by Nernst equation

(3) There are more proteins in the plasma than in the IF
C: Gibbs-Donnan equilibrium will affect ion movement across capillary walls

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19
Q

Calculates the equilibrium potential at a given concentration difference of a permeable ion across cell membrane

A

Nernst equation

EMF = 61+log concentration inside/conc. outside

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20
Q

Signs to remember in Nernst equation

A

sign of potential is (+) if diffusing ion is a negative ion

sign of potential is (-) if diffusing ion is a positive ion

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21
Q

Calculates the membrane potential in the inside of a membrane when a membrane is permeable to several different ions

A

Goldman-Hodgkin-Katz Equation

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22
Q

Measured potential difference across the cell membrane in millivolts (mV)

A

RMP

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23
Q

Intracellular potential relative to the extracellular potential

A

RMP

RMP of -70 means 70mV cell negative

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24
Q

Characteristics of EMP

A

Established by diffusion potentials that result from concentration differences of permeable ions
Each permeable ion attempts to drive the membrane potential toward its equilibrium potential

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25
Q

ORIGIN OF RMP

A

Contribution of K+ Diffusion Potential
Contribution of Na+ Diffusion
Contribution of Na/K ATPase

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26
Q

If potassium ions were the only factor causing the resting potential, the resting potential INSIDE THE FIBER would be equal to ________

A

-94 millivolts

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27
Q

Potassium vs Sodium in Diffusion and Permeability

A

Diffusion of K contributes far more to membrane potential than diffusion of Na
Permeability to K is about 100 times as great as its permeability to Na

28
Q

Contribution of Na/K ATPase to the Original RMP

A

Direct electrogenic contribution of the pump (3Na2K) is small
This creates an additional degree of -4mV

29
Q

Short range change in voltage
Incoming Na ions diffuse for short distances inside the plasma membrane
Produce a current that travels from the point of stimulation toward the cell’s trigger zone

A

LOCAL POTENTIALS

30
Q

Any change in which membrane voltage shifts to a less negative value

A

Depolarization

31
Q

Two possible effects of Depolarization

A

Local potential - generation of a nonpropagated response

Action potential - generation of a propagated response

32
Q

Characteristics of LOCAL POTENTIAL

A

Graded. (Stronger the stimulus, stronger the response)
Decremental. (Gets weaker as they spread from point of stimulation)
Reversible. (If stimulation ceases, K diffusion out of cell to return membrane voltage to its resting potential)
Either Excitatory or Inhibitory.
Excitatory - produce an action potential
Inhibitory - less likely to produce an action potential

33
Q

Types of Local Potential

A

Synaptic Local Potentials
Generator/Receptor Potentials
Electrotonic Potentials

34
Q

Alteration in the Membrane Potential of cell resulting from activation at the synapse

A

Synaptic Potential

35
Q

Types of Synaptic Potential

A

Excitatory Post-Synaptic Potential - Intracellular voltage increases
Inhibitory Post-Synaptic Potential - Intracellular voltage decreases

36
Q

Transmembrane potential difference produced in sensory receptor
Occurs as depolarization resulting from inward current flow

A

Generator/Receptor Potential

37
Q

Influx of current will often bring the membrane potential of the sensory receptor towards the threshold for triggering an action potential

A

Generator/Receptor Potential

38
Q

Passive spread of charge inside a neuron due to local changes in ionic conductance
Ionic charge enters in one location and dissipates to others, losing intensity as it spreads (graded response)

A

Electrotonic Potential

39
Q

Rapid changes in the membrane potential that spread along the nerve fiber

A

Action Potential

40
Q

How do you conduct a nerve signal

A

The action potential moves along the nerve fiber until it comes to the fiber’s end

41
Q

Characteristics of Action Potential

A

Follow All-or-None Law. If stimulus depolarizes neuron to threshold, neuron fires at its maximum voltage. Above threshold, stronger stimuli do not produce stronger action potential.

Nondecremental. AP do not get weaker with distance

Irreversible. AP goes to completion. AP cannot be stopped once it begins.

42
Q 
Fill the table.
Parameter                LOCAL POTENTIAL             ACTION POTENTIAL
Mediator
Voltage Change
Intensity
Reversibility
Distance of Effect
Progression
A

Parameter LOCAL POTENTIAL ACTION POTENTIAL
Mediator Ligand-gated ion channels Voltage-gated ion channel
Voltage Change Depolarizing/Hyperpolarizing Depolarizing
Intensity GRADED ALL-OR-NONE
Reversibility Reversible Irreversible
Distance of Effect Short (Local) Long (distant)
Progression Decremental Non-decremental

43
Q

Steps in the Generation of Action Potential

A

Resting Stage - RMP, before AP begins, -90mV
Depolarization - Threshold potential is reached (-65mV)
Voltage-gated Na overwhelm K+, permeable to Na ions
Overshoot - great excess of positive Na ions causes MP to overshoot
beyond the zero level

44
Q

Ionic Basis of Depolarization

Necessary factor in both depolarization and repolarization of the nerve membrane

A

Voltage-Gated Sodium Channel

45
Q

Feedback Control of Depolarization

A

Positive Feedback

46
Q

Sodium channels begin to close and the K channels open more than normal
Rapid diffusion of K ions to the exterior reestablishes resting membrane potential

A

Repolarization

47
Q

Ionic Basis of Repolarization

Also plays an important role in increasing the rapidity of repolarization of the membrane

A

Voltage-Gated Potassium Channel

48
Q

Feedback Control of Hyperpolarization

A

Negative Feedback

49
Q

Afterhypolarization
K+ conductance remains higher than at rest after closure of the Na+ channels
Membrane potential is driven very close to the K+ equilibrium potential

A

Undershoot

50
Q

Effects of Ion Fluxes on Action Potential
Structure Contribution
K+ leak channel
Na+/K+ ATPase pump
Voltage-gated Na+channels
Voltage-gated K+ channels

A

Structure Contribution
K+ leak channel Resting Membrane Potential
Na+/K+ ATPase pump Maintenance of the Concentration gradient
Voltage-gated Na+channels Depolarization and Hyperpolarization
Voltage-gated K+ channels Hyperpolarization

51
Q

Effect on

DECREASE extracellular Na+ concentration

A

Reduce the size of AP

No effect on RMP

52
Q

Effect on:

INCREASE extracellular K+ concentration

A

Decrease RMP

53
Q

Effect on:

DECREASE extracellular Ca2+ concentration

A

INCREASE excitability

DECREASE threshold

54
Q

Effect on:

INCREASE extracellular Ca2+ concentration

A

DECREASE excitability

INCREASE threshold

55
Q

Effect on:
INCREASE intracellular Cl- concentration
INCREASE intracellular Protein concentration

A

DECREASE RMP

56
Q

How are AP propagated?

A

By the spread of local currents to ADJACENT areas of membrane, which are then depolarized to threshold and generate action potentials

57
Q

Direction of AP Propagation

A

No single direction of propagation

An AP travels in both directions away from the stimulus until the entire membrane has become depolarized

58
Q

Depolarization process travels over the entire membrane if conditions are right, or it does not travel at all if conditions are not right

A

All-Or-Nothing Principle

59
Q

Factors Affecting Conduction Velocity

A

Fiber Size - Increase diameter, faster

Myelination - myelin acts insulator; saltatory conduction (5-50 fold)

60
Q

Action potentials can be generated only at gaps in the myelin sheath called as

A

Nodes of Ranvier

61
Q

Importance of Saltatory conduction

A

It conserves energy for the axon

Only the nodes depolarize, allowing 100 times less loss of ions than would otherwise be necessary

62
Q

Time periods after an action potential during which new stimulus cannot be readily elicited

A

Refractory Period

63
Q

Another AP cannot elicited, no matter how large the stimulus is
Coincides with almost the entire duration of the action potential

A

Absolute Refractory Period

64
Q

Ionic basis of Absolute Refractory Period

A

Inactivated gates of Na+ channel are closed when membrane potential is depolarized and remain closed until repolarization occurs
No AP can occur until the inactivations gates open

65
Q

Begins at the end of the Absolute refractory period and continues until the membrane potential returns to the resting level
AP ca be elicited only if a larger than usual inward current is provided

A

Relative Refractory period

66
Q

Ionic Basis of Relative Refractory Period

A

K+ conductance is higher than the rest
MP is closer to the K+ equilibrium potential and farther from the threshold
More inward current is required to bring the membrane to threshold

67
Q

Integral proteins that span the cell membrane

When open, permit the passage of certain ions

A

Ion Channels

PHYSIOLOGY (13 decks)

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