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DEN 7101S Human Structure and Function II > 1/3 Britton Neuronal Action Potentials > Flashcards

1/3 Britton Neuronal Action Potentials Flashcards

1
Q

_____ separates the ICF and ECF compartments

A

Plasma membrane

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2
Q

Plasma membrane consists of:

A
  • phospholipid bilayer
  • Membrane bound proteins that permit communication (ion channels, transporters, receptors)
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3
Q

Transport of ions and small H2O-soluble molecules across the cell membrane requires:

A

Membrane transport proteins

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4
Q

Types of membrane transport pathways

A
  • simple diffusion
  • facilitated diffusion
  • active transport
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5
Q

Examples of plasma membrane transporters

A
  • ion channels
  • ATP dependent pumps
  • carrier proteins
  • channel proteins
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6
Q

Carrier proteins are used for:

A
  • facilitated diffusion
  • active transport
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7
Q

Channel proteins are used for:

A

Simple diffusion

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8
Q

Approximate concentration of Na+ (in/out)

A
  • Outside: 140
  • Inside: 14
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9
Q

Approximate concentration of K+ (in/out)

A
  • Outside: 4
  • Inside: 120
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10
Q

Approximate concentration of Cl- (in/out)

A
  • Outside: 105
  • Inside: 10
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11
Q

Approximate concentration of Ca2+ (in/out)

A
  • Outside: 2.5
  • Inside: <1
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12
Q

A fluid that is composed of 120 mM K+, 12 mM Na+, and 15 mM Cl- but is virtually Ca2+ free would best approximate which body fluid compartment?

A

Intracellular

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13
Q

Excitable cells have the ability to be ____

A

electrically excited

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14
Q

Examples of excitable cells

A
  • neurons
  • muscle cells (skeletal, cardiac, smooth)
  • some endocrine cells (pancreatic beta cells)

Mnemonic: MEN are easily excited (muscle, endocrine, neuron)

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15
Q

Excitable cells have an ______ across the cell membrane

A

Electrical potential difference

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16
Q

What is an electrical potential difference?

A

A charge difference

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17
Q

Electrical potential difference between inside and outside of the cell is called:

A

Membrane potential (Vm)

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18
Q

Membrane potential is a function of:

A

relative permeability for K+ versus Na+

Whether the channels are opened or closed

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19
Q

Membrane potential values depend on _____ and can range from ____

A

Cell type; -30 to -90 mV

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20
Q

Membrane potential of a nerve cell at rest is generally:

A

-70 mV

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21
Q

How is membrane potential measured?

A

Via inserting a small recording microelectrode inside the cell to measure the potential difference across cell membrane

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22
Q

Membrane potential is always expressed as:

A

Voltage inside the cell relative to the outside

-20 mV means inside is negative compared to the outside

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23
Q

Membrane potential is determined by several factors, which are:

A
  • concentration of +/- ions across the cell membrane
  • membrane pumps and transporters that transport ions across the cell membrane
  • relative permeability of cell membrane to these ions (open or closed channels)
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24
Q

Example of a key membrane transporter

A

Na+/K+ ATPase

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25
Q

______ establishes the concentration gradient for Na+ and K+ ions and is important for maintaining ______

A

Na+/K+ ATPase; cell resting potential

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26
Q

Na+/K+ ATPase pumps out ____ and pumps in ____

A

3 Na+; 2 K+

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27
Q

What is digoxin used to treat?

A

Heart failure

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28
Q

Examples of drugs that target Na+/K+ ATPase

A
  • Digoxin
  • Ouabain
  • Digitalis glycosides

Disrupts Na+/Ca2+ exchanger as a result

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29
Q

Ion channels are membrane proteins that span the plasma membrane _____

A

Repeatedly

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30
Q

Ion channels have distinct structural features, including:

A
  • Pore through which ions can diffuse across the membrane
  • Several transmembrane domains
  • Selectivity filter
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31
Q

True or false: ion channels allow many different ions to pass through

A

False - they are selective for a particular ion, uses a selectivity filter

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32
Q

Ion channels are gated by a mechanism that _____

A

Opens or closes the channel pore

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33
Q

Gating mechanisms that open and close channels

A
  • Voltage-gated
  • Ligand-gated
  • Mechanically-gated
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34
Q

Voltage-gated ion channels open by:

A

Changes in membrane voltage

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35
Q

Ligand-gated ion channels open after:

A

Binding of a ligand to a receptor site on the channel

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36
Q

Mechanically-gated ion channels open with:

A

Membrane stretch

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37
Q

Ion channels control the ______ to ions and thus play a primary role in ______

A

Membrane permeability; the electrical behavior of excitable cells

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38
Q

Voltage gated Na+ channels have ____ gates, which are:

A

2; activation and inactivation gate

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39
Q

In an open-state voltage gated Na+ channel:

A

Na+ ions flow down electrochemical gradient

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40
Q

Na+ channels exist in what 3 states during the phases of the action potential?

A
  • rested-closed
  • activated-open
  • inactivated-closed
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41
Q

______ is the driving force for ion movement across the cell membrane

A

Electrochemical gradient

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42
Q

Electrochemical gradient consists of what 2 forces?

A
  • Chemical gradient
  • Electrical gradient
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43
Q

A chemical gradient is present when there is:

A

A difference in concentration of a chemical across a membrane

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44
Q

An electrical gradient is present when there is:

A

Difference in charge across a membrane

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45
Q

At electrochemical equilibrium:

A

Chemical and electrical driving forces acting on an ion are balanced

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46
Q

True or false: there is no further diffusion of an ion across the membrane when electrochemical equilibrium is reached

A

True (and even if channel is open)

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47
Q

How can we calculate equilibrium potential for a particular ion?

A
  • Nernst equation/potential
  • need [ICF] and [ECF]
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48
Q

What is the equilibrium potential for Na+?

A

+60 mV

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49
Q

What is the equilibrium potential for K+?

A

-90 mV

50
Q

What is the equilibrium potential for Ca2+?

A

+130 mV

51
Q

What is the equilibrium potential for Cl-?

A

-63 mV (but can vary)

52
Q

The resting membrane potential of nerve cells is ____ and is close to the equilibrium potential of what ion?

A

-70 mV; K+

53
Q

Action potentials are _____ signals, often called _____

A

Electrical; electrical impulses

54
Q

____ are the basis of information transfer in nerves

A

Electrical signals (AP’s)

55
Q

Examples of electrical signals

A
  • transmit sensory information
  • initiate an action like contraction of a muscle or secretion from a gland

Think about afferent and efferent (sensory and motor)

56
Q

An action potential is a ____ in membrane potential and goes from _____ to ____ and back to _____

A

Transient change; negative to positive; negative

57
Q

In nerves, during an AP, Vm changes from resting Vm ____ to ____, termed a _______

A

-70 mV; +30 mV; depolarization

58
Q

After an AP is initiated, Vm returns to resting negative value after _____. Termed _____

A

1 msec; repolarization

59
Q

_____ are active responses generated by changes in the permeability of the neuronal membrane

A

AP’s

60
Q

In the resting state for neurons, Na+ channels are ____. K+ channels are ______

A

Closed; open

Efflux of K+ ions making inside negative (resting Vm close to Ek)

61
Q

What happens to a neuron when it becomes excited by a stimulus?

A
  • Na+ channels open and cause rapid influx of Na+ ions into the cell
  • positive charge movement into the cell causes a depolarization and inside of cell is now +30 mV
62
Q

When Na+ channels open during an AP, why is there a rapid influx of Na+?

A
  • Concentration gradient (less Na+ inside)
  • Electrical gradient (inside is negative at rest, attracts positive Na+)
63
Q

After a depolarization during an AP, Na+ channels _____ after 1 msec. But, ____ are open and additional _____ now open. ____ flows out of the cell according to their ______, creating a ____ potential inside the cell, termed a _____

A

Close (inactivate); K+ channels; voltage-gated K+ channels; K+; electrochemical gradient; negative; repolarization

64
Q

During repolarization, what happens to the membrane potential?

A

Moves back to resting Vm -70 mV and even beyond (hyperpolarization)

65
Q

Why does hyperpolarization occur?

A

Because of additional movement of K+ through voltage gated K+ channels

66
Q

Once the voltage gated K+ channels close after an AP, the membrane will return to the resting potential maintained initially by ____

A

K+ leak channels

67
Q

______ is a change more positive than the resting membrane potential

A

Depolarization

68
Q

____ is when the membrane potential becomes more negative than the resting membrane potential

A

Hyperpolarization

69
Q

____ is the return of the membrane potential towards resting Vm following either depolarization or hyperpolarization

A

Repolarization

70
Q

_____ is the level to which membrane potential must be depolarized to initiate an action potential

A

Threshold potential

71
Q

Explain the characteristic phases of an action potential due to specific changes in the membrane permeability to Na+ and K+

A
  • K+ leak channels maintain resting potential
  • upon stimulus, K+ channels close and Na+ channels open to cause depolarization
  • Na+ channels close, K+ channels reopen and open voltage gated K+ channels (repolarization/hyperpolarization)
  • Voltage-gated K+ channels close, K+ leak stays open to maintain resting Vm
72
Q

True or false: AP’s have a threshold potential for activation

A

True

73
Q

For a typical neuron, the threshold potential is near ____

A

-55 mV

74
Q

For activation gates of Na+ channels to open, there needs to be ______

A

Sufficient current that exceeds threshold potential

75
Q

True or false: small depolarizations that do not reach threshold may result in an AP

A

False - do not (all or nothing principle)

76
Q

The intensity of a stimulus is encoded in ____, not _____

A

Frequency of AP’s; AP amplitude

77
Q

True or false: bigger stimuli elicit a bigger AP

A

FALSE - do not change AP amplitude!

78
Q

The amplitude of an AP is independent of _____

A

Magnitude of the stimulus used to evoke it

79
Q

Multiple AP’s with increased frequency occur when:

A

the intensity or duration of a stimulus is reached

80
Q

Absolute refractory period

A

Interval of time during an AP in which another AP absolutely cannot be generated

81
Q

Why is there an absolute refractory period?

A

Na+ channels inactivate after opening, and are unable to open again until the gate is reset

82
Q

In a relative refractory period, a 2nd AP can be initiated, but:

A

Will require a greater stimulus than before

83
Q

How do AP’s move along the axon?

A

They are propagated

84
Q

AP is generated at the ___ and propagates along the ____

A

Axon hillock; axon

85
Q

How does axon propagation occur?

A
  • Current that flow inward at a point on the axon during an AP spread out along the axon and depolarize the adjacent sections of the axon membrane
  • when this depolarization reaches threshold, a new AP is generated at the new location
86
Q

AP propagation cannot reverse direction due to:

A

Refractory periods

87
Q

____ and ____ affect AP conduction speed

A

Axon diameter and myelination

88
Q

Larger diameter axons have a ____ AP conduction velocity due to _____ for ion flow during AP propagation

A

Faster; less resistance

89
Q

Myelinated axons have a ____ AP conduction velocity as APs are propagated from ____ to _____

A

Faster; Node to node of ranvier

90
Q

Can ions flow through myelin sheath?

A

No

91
Q

Can ions flow through the node of ranvier?

A

Yes, with ease

92
Q

What is concentrated at nodes of Ranvier?

A

Na+ and K+ channels

93
Q

In myelinated axons, APs are propagated from node to node rather than conducting along the whole nerve membrane. This is termed _____

A

Saltatory conduction

94
Q

Why is saltatory conductance of value?

A
  • conduction is faster
  • conserves energy for the axon (less energy required via Na+/K+ pump)
95
Q

Multiple sclerosis

A
  • degeneration of myelin sheath
  • decrease in nerve transmission
96
Q

Nerve fibers are often classified according to their:

A

Conduction velocity

97
Q

Order of fastest to slowest nerve fibers

A
  • A alpha
  • A beta
  • A gamma
  • A delta
  • B
  • C
98
Q

Which nerve fiber is not myelinated

A

C

99
Q

Large axon diameter and myelination result in _____ conduction velocities

A

Faster

100
Q

A-type nerve fibers are mostly involved in:

A

Sensory and motor functions

101
Q

Several drugs inhibit nerve excitability, such as:

A
  • Local anesthetics
  • Tetrodotoxin (TTX)
  • a-toxins and beta-toxins
  • Batrachotoxin
102
Q

Examples of local anesthetics

A
  • lidocaine
  • procaine
  • tetracaine
103
Q

What is tetrodotoxin?

A
  • potent neurotoxin
  • found in pufferfish and blue-ringed octopus
104
Q

a- and beta-toxins come from:

A

Scorpion venom

105
Q

Batrachotoxin comes from:

A

S. American frogs “poison dart” of Indian arrows

106
Q

Local anesthetic prevents or relieves pain by:

A

Interrupting nerve conduction

107
Q

Most local anesthetics act directly on:

A

Activation gates of Na+ channels

108
Q

LA’s make it difficult for ____ to open, thereby reducing ____

A

Na+ channels; membrane excitability

109
Q

Partial or full blockade of Na+ channels will result in:

A
  • decrease in the magnitude of depolarizing Na+ current
  • increase in threshold for firing an AP
110
Q

As the number of Na+ channels blocked by LA channels increases, _____ slows

A

AP propagation

111
Q

True or false: LA inhibition of Na+ channels is reversible

A

True

112
Q

In use of local anesthetics, AP conduction fails when:

A

Depolarizing current preceding the propagated AP is insufficient to reach threshold in the adjacent patch of nerve membrane

113
Q

True or false: All nerves are blocked equally by LA’s

A

False

114
Q

LA sensitivity may depend on multiple factors, such as:

A
  • Myelination
  • Axon diameter
  • level of nerve activity
  • Nerve function
  • Differences in density of ion channels or location of a nerve fiber within a large nerve trunk
115
Q

In general, myelinated axons are _____ to LA blockade than unmyelinated axons

A

More sensitive

116
Q

____ diameter axons are more sensitive to LA action

A

Smaller

117
Q

Nerves with ____ firing rates are more sensitive to LA blockade

A

Higher (LA may get better access to Na+ channel when in activated state)

118
Q

LA blockade may be stronger in sensory or motor nerves?

A

Sensory nerves (tend to fire APs at higher frequencies compared to motor nerves)

119
Q

Motor fibers are often located in the ___ portion of the bundle and are more or less accessible to LA?

A

Outer; More

motor fibers may be blocked before sensory fibers in large mixed nerves

120
Q

_____ is usually the first modality to disappear after LA injection

A

Pain

121
Q

LA produces an orderly progression of loss of:

A
  • temperature sensation
  • proprioception
  • sensation
  • light touch
  • motor function

Variation among patients and different nerves is considerable

DEN 7101S Human Structure and Function II (21 decks)

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