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Flashcards in Intro to Electrophysiology Deck (104):
1

A voltage difference or separation of charge between the internal and external surfaces of the plasma membrane

Membrane potential

2

At rest, the membrane is

Polar

3

In general, the internal surface region of the plasma membrane has what charge?

Negative

4

In general, the extracellular surface region of the plasma membrane has what charge?

Positive

5

The inner surface of the plasma membrane is negative relative to the

-does not mean it is loaded with negative charge

Extracellular surface

6

The resting membrane potential of a large nerve is maintained at approximately

-90 mV

-means inner membrane is 90 mV less positive than outer

7

The flow of charge (ions)

Current

8

The resting membrane potential is due in large part to the membrane distribution of

Na+ and K+

9

Located inside the cell and help establish the resting membrane potential

Negatively charged proteins and Cl-

10

Generated any time an ion translocates across the cell membrane

Current (I)

11

Cell and tissue function is controlled by

Ion flux

12

In a resting motor neuron, there is a high intracellular concentration of K+ as compared to a high extracellular concentration of

Na+

13

Because of its chemical concentration gradient, there is a strong driving force for the translocation of K+ out of the cell through

K+ leak channels

14

Na+ and K+ are moved across the membrane against their concentration gradients by the

-maintains net negative charge on inner face of membrane

Na+/K+ ATPase (3 Na+ out, 2 K+ in)

15

How many ATP molecules are used during each ATPase cycle?

One

16

The tendency for an ion to move in one direction or another

Electromotive Force (EMF)

17

Dependent on the intra- and extracellular concentrations of Na+, K+, and Cl-, as well as membrane permeability of these ions

EMF

18

By maintaining RMP at around -90 mV, there exists a tremendous electrochemical gradient for the movement of Na+ inward, which is the defining characteristic of

Membrane depolarization during action potential

19

What are four electrogenic tissues that are dependent oupon anions (Cl-) and cations (Na+, K+, Mg2+, and Ca2+) for electrogenecity?

Heart, Skeletal muscle, Neurons, Vascular smooth muscle, and GI smooth muscle

20

The resting membrane potential is set by the membranes concentration gradient for

K+ out of the cell

21

The larger the K+ concentration gradient (i.e. the ratio of intracellular K+ to extracellular K+), the greater the

Nagtivity in the cell

22

When the the plasma [K+] is elevated (i.e. during hyperkalemia), the concentration gradient across the cell membrane is lowered; and this drives the

Resting membrane potential to be less negative (Membrane depolarizes)

23

Neurons communicate via the electrochemical phenomenon known as an

Action potential

24

The plasma membranes of neural and muscle cells contain voltage-gated Na+, K+, Cl-, and/or Ca2+ channels that open/close when there is a specific change in

Membrane potential

25

Causes the initial upward phase of the action potential (membrane depolarization)

Na+ flux

26

The action potential can be recorded and measured as

Electric current (INa+)

27

Rapid (< 0.1 msec) changes in membrane potential that result from alterations in the permeability of the membrane to Na+ and K

Neuronal Action Potentials

28

What are the three phases of the action potential?

1.) Resting
2.) Depolarization
3.) Repolarization

29

When the nerve fiber is at resting membrane potential

Resting phase

30

Characterized by acute changes in the membrane potential, which result in increased permeability of the plasma membrane to Na+ due to inactivation of resting voltage gated Na+ channels

Depolarization phase

31

Describe the depolarization phase of an action potential

Na+ rushes into the cell through open (active) Na+ gated channels, this results in the membrane potential becoming less negative, and more Na+ channels are activated, thus increasing influx of Na+

32

The membrane potential at which I-Na+ overcomes any opposing forces to inward I-Na+ and I-Na+ becomes self-reinforcing rapidly driving membrane potential toward the Nernst equilibrium potential for Na+

Threshold potential (Usually around -70 - -60 mV)

33

The changes in membrane potential resulting from depolarization induce the opening of

Voltage-gated K+ channels

34

Peak opening of the voltage gated K+ channels has occured at around

60 mV

35

What happens during the Repolarization phase?

Na+ channels close, but K+ channels remain open for a while allowing the membrane potential to become more negative. Then Na+/K+ ATP restore the resting membrane potential

36

Voltage-gated Na+ channels have 2 gates in series.

1.) One is located more toward the extracellular side and is called the
2.) One is located more towards the cytoplasmic side and is called the

1.) Activation gate
2.) Inactivation gate

37

If either gate of the Na+ voltage-gated channel is closed, then the channel is

Inactive

38

What is the resting conformation of a Na+ channel?

Activation gates = closed
Inactivation gates = open

39

This specific conformation is important because Na+ channels can only be activated from the

Resting conformation

40

The majority of activation gates rapidly open in response to the

Threshold potential (about -60 mV)

41

During repolarization, both gates of the Na+ channel are

Closed (inactive conformation)

42

In the event of elevated extracellular K+
(i.e. severe enough hyperkalemia), RMP will be driven less negative; in so doing lessening the potential difference between

Resting membrane potential (RMP) and threshold

43

Decreasing the potential difference between RMP and threshold has what effect on neuromuscular tissue?

Makes them more excitable (irritable)

44

This excitability is very short lived because hyperkalemia depolarizes neuromuscular tissues and promotes inactivation of

Resting Na+ channels

-impedes generation of action potentials

45

Are comprised of a single gate

-possess both a voltage and time dependency

K+ Channels

46

During RMP, the gate is closed and the voltage-gated K+ channel is

Inactive (resting)

47

Upon depolarization to suprathreshold levels (> -60 mV), the K+ gate opens somewhat gradually, with the greatest percentage of K+ channels open around

60 mV

48

K+ channels change between conformations slowly. As membrane potential returns towards RMP, voltage-gated K_ channels remain open for several msec, resulting in a brief period of

Membrane Hyperpolarization

49

Another contributor to the generation of an action potential

Calcium

50

In cardiac myocytes and smooth muscle cells, the depolarization scheme is dominated by

Ca+ pumps/channels

51

By comparison to voltage-gated Na+ channels, voltage-gated Ca2+ channels are

Slow activating

52

What are the two important types of calcium channels?

L (long) type and T (transient) type

53

Activate and inactivate over more negative membrane potentials and therefore assist in the pacemaker function of the sinoatrial node

T-type channels

54

Have a high threshold for activation (> -30 mV), and sustain the plateau phase of the action potential found in cardiac myocytes and vascular smooth muscle

L-type channels

55

Under normal circumstances, any even that depolarizes membrane potential to threshold level will initiate an

Action potential

56

Not all depolarizations reach

Threshold

57

A subthreshold stimulus initiates subthreshold alterations in membrane potential by activating

-allows for Na+ influx

LIGAND-gated Na+ channels

58

Subthreshold changes in membrane potential are referred to as

-Proportional in amplitude to the stimulus strength

Graded potentials

59

Graded potentials can sum to reach

Threshold

60

The excitability of neuromuscular tissue is dependent upon the difference between

Resting potential (Em) and Threshold potential (Et)

= Em - Et

61

Another action potential can not be initiated when the Na+ channels are

Closed (inactive)

62

Period of time following peak action potential, where all voltage-gated Na+ channels are inactive (closed)

-extends until sufficient numbers of voltage-gated Na+
channels return to the resting conformation

Absolute refractory period

63

The recovery phase where enough Na+ channels have returned to resting that a relatively strong (suprathreshold) stimulus can initiate another action potential

Relative refractory period

64

Sodium that has entered the neuron (during depolarization) spreads to neighboring sections of the

Plasma Membrane

65

The migration of Na+ to neighboring sections of the plasma membrane induces which three things?

1.) Depolarization of adjacent regions to threshold
2.) Activation of restive voltage-gated Na+ channels
3.) The resultant action potential in adjacent areas of membrane

66

Thus, an action potential is propagated from the initial activation site, along the membrane, via a series of

Na+-induced depolarizations

67

Travel to the nerve terminus and/or soma and stimulate a response such as the release of neurotransmitters, or the opening of other types of voltage-gated ion channels (e.g., Ca2+ channels)

Action potentials

68

A phospholipid/cholesterol based substance that is formed by Schwann cells within certain types of neuronal tissue

Myelin

69

The presence of the myelin sheath prevents conductivity, hence AP are not generated within

Myelin

70

Within myelinated neurons, an action potential can only be generated within the

Nodes of Ranvier

71

Propagation of an action potential from node to node

-requires less energy than the cable-like conduction in non-myelinated neurons

Saltatory conduction

72

The maintenance of normal cardiac rate and rhythm is directed by the pacemaker activity of a population of electrogenic cells collectively known as the

Sinoatrial node

73

Undergo rythmic depolarization and repolarization in the absence of innervation

SA nodes

74

The concerted activities of T-type Ca2+ channels, Na+ HCN channels, and K+ channels enables inward ICa2+ and If (funny current = Na+) and outward IK+ within the

SA node

75

To begin one pacemaker cycle, inward ICa2+ and If, combined with outward IK+, enable a

Gradual depolarization

76

As the membrane potential creeps toward -55 mV, voltage-gated Ca2+ channels are increasingly activated, producing a rapid upstroke in

Action potential

77

T-type Ca2+ channels inactivate through the depolarization phase, and at about 0 mV HCN channels are inactivated, shutting down If, and thus allowing repolarization via

Ik+

78

Repolarization leads to a brief period of hyperpolarization which is necessary to reactivate

HCN channels

79

Relatively long duration APs which are named due to a characteristic plateau-shaped phase following depolarization

-ex: potentials regulating cardiomycete contractility

Plateau Potential

80

The plateau of the plateau potential is the result of K+ channels, which cause repolarization, being countered by

Ca2+ channels (activated by Na+ AP)

81

Somatic sensory receptors that mediate the pain signal

-activated during injury by factors such as bradykinin, substance P, etc

Nociceptors

82

The sensations of acute and chronic somatic pain are mediated by

Nociceptors

83

Nociceptor afferents (nerve fibers relaying into the central nervous system) consist of

Myelinated and unmyelinated fibers

84

The myelinated fibers are type Aδ fibers, which mediate the relay of so-called

Fast pain (Sharp/intense pain)

85

Working with type Aδ fibers are the populations of small diameter, unmyelinated, slow conducting pain afferents called

Type C fibers

86

Relay the sensation of dull, burning pain

Type C fibers

87

Pain afferents feed into the dorsal horn of the spinal cord and ascend specific tracts to the

Thalamus

88

Work by reversibly blocking action potentials in pain afferents

Local Anesthetics

89

In general these agents exist as weak bases (deprotonated) at physiologic pH (7.4), are lipid-soluble, and because of their hydrophobic nature preferentially
enter small diameter pain afferents

Local Anesthetics

90

Local anesthetic molecules are ionized by the acidic intracellular pH of the neuron, which enables them to bind

Voltage-gated Na+ channels (confers inactive conformation)

91

The process whereby action potentials are relayed between neurons and/or between neurons and affector tissues

Synaptic transmission

92

Neuromuscular transmission utilizes the neurotransmitter

Acetylcholine (ACh)

93

There are numerous neurotransmitters used for neuroneuronal transmission. The ubiquitous excitatory neurotransmitters are

Gluamate and aspartate

94

Common inhibitory neurotransmitters are

GABA and glycine

95

Chemical synaptic transmission is subcategorized into

Ionotropic and metabotropic

96

Utilizes neurotransmitters to activate ligand-gated ion channels residing in the post synaptic membrane

Ionotropic transmission

97

An example of an excitatory ionotropic system

-found in skeletal muscle

Nicotenic-cholinergice receptor (ACh = neurotransmitter)

98

What is faster, ionotropic or metabotropic transmission?

Ionotropic

99

Relies upon not only the release of chemical neurotransmitters, but the activation of receptor-mediated signaling in the effector tissue by the neurotransmitters

Metabotropic transmission

100

The AChmediated activation of cholinergic-muscarinic receptors within the sinoatrial node, which results in K= exiting the cell, used to control heart rate is an example of

Metabotropic transmission

101

Terminated by enzymatic dissociation of the neurotransmitters and/or re-uptake of the neurotransmitter by the pre-synaptic terminus

Neuronal Transmission

102

Can occur following the sustained stimulation of
neuronal transmission, such as what would occur in the presence of a cholinesterase inhibitor

Synaptic fatigue

103

Results from exhaustion of neurotransmitter reserves, desensitization of the postsynaptic receptors, and/or disruptions in local ionic gradients within the post synaptic neuron such that the stimulatory signal is dampened or terminated

Synaptic fatigue

104

ACh binding to the nicotinic-cholinergic receptor induces a conformational change in the channel receptor structure, which increases its permeability to

Na+, Ca2+, and K+

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