SDL: Action Potential Flashcards

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1
Q

the resting membrane potential

A

-70 mV

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2
Q

the phases of the action potential

A

rising phase, overshoot, peak, falling phase, after hyperpolarization

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3
Q

the ionic concentrations of a neuron are set up such that Na+ ions..

A

would be driven INTO the neuron along both its electrical and conc. gradients (if there are sufficient channels)

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4
Q

the large increase in permeability of Na+ allows for

A

a large Na+ inward current (depolarization)

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5
Q

the equilibrium potential for Na+

A

+60 mV (membrane potential approaches this but does not reach it)

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6
Q

what happens to ion channels at the threshold potential?

A

some voltage-gated Na+ selective channels open, increasing the permeability of the membrane to Na+

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7
Q

the 2 gates that Na+ channels have

A

activation/deactivation gate + inactivation/deinactivation fate

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8
Q

when the membrane potential is +, the electrical and the concentration gradients for K+ drive K+..

A

OUT of the cell

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9
Q

the resulting efflux of K+ causes which phase?

A

falling (repolarization), but it overshoots, causing the after hyperpolarization

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10
Q

effects of tetrodotoxin

A

blocks voltage-gated Na+ channels

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11
Q

effects of tetraethylammonium ions

A

block voltage-gated K+ channels

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12
Q

since potentials die out within a few millimeters, longer distance transmission of action potentials requires..

A

a system that regenerates the action potential along the axon

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13
Q

what causes eddy currents?

A

at threshold, voltage-gated Na+ channels open and Na+ rushes in, causing eddy currents from outside to the inside of the membrane; these evoke more eddy currents and propagate the AP

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14
Q

what is saltatory conduction?

A

when the AP skips from node to node on myelinated axons

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15
Q

myelinated fibers sequester voltage-gated K+ channels, so how does repolarization of the action potential occur? what does this prevent? Why is this important?

A

LEAKAGE of K+ channels that are not actively opened; this produces no-hyperpolarization, so the AP can be conducted at a faster rate

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16
Q

what happens to the voltage gated channels in demyelinating diseases like MS?

A

slow conduction occurs, and the voltage gated channels may be incorrectly distributed, so there is insufficient mechanisms to conduct an AP

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17
Q

what is the absolute refractory period?

A

during the spike part of the AP, the membrane cannot initiate another AP

18
Q

what is the relative refractory period?

A

during the early part of the after-depolarization part, another AP can be initiated if stimulus is increased in strength

19
Q

what is the subnormal period?

A

the after hyperpolarization phase: K+ channels still open and membrane potential is near equilibrium for K+, but another AP can be elicited by a stimulus if it is large enough to shift the MP to threshold. (Na+ channels will already be reset)

20
Q

what is orthodromic conduction?

A

normal conduction direction from the AP, away from the soma

21
Q

what is antidromic conduction?

A

conduction of AP toward the soma

22
Q

what is an electrotonic/graded potential?

A

changes in cytoplasmic membrane potential, but not sufficient to propagate an action potential

23
Q

what are examples of the normally occurring electrotonic potentials?

A

the excitatory and inhibitory synaptic ones and those at all sensory receptors

24
Q

how can neuropathy be tested for?

A

fibers in a nerve can be stimulated by an electrical pulse to a cathode placed near a nerve (no flow of ions across the membrane).

25
Q

if a cathode (neg pole) is placed near a near fiber, and there is an applied stimulus, the nerve fiber adjacent to the cathode will be..

A

depolarized

26
Q

if the anode (pos pole) is used, the membrane will be..

A

hyperpolarized

27
Q

example of mechanical pressure changing ions across the membrane

A

striking the “funny bone”

28
Q

neuropathy is caused by

A

unhealthy nerve fiber with slowed conduction velocity

29
Q

what is depolarization block? what causes it?

A

when the membrane potential remains above the threshold- can’t be repolarized; hypoxia or anoxia

30
Q

amount of time the soma of a neuron can tolerate anoxia before the cell is killed

A

4 minutes

31
Q

describe what is happening when limbs “go to sleep”

A

nerve fibers depolarize due to lack of energy to maintain membrane potential; when the MP does repolarize, numerous APs are initiated

32
Q

what is hyperpolarization block?

A

when the MP is maintained below the resting potential level

33
Q

drugs/events that cause hyperpolarization block

A

novocaine, lidocaine, hypoxia

34
Q

what do local anesthetics block?

A

voltage-gated Na+ channels

35
Q

what happens in an injury current?

A

severed nerve allows electrical currents to flow across a gap in the membrane for a short time

36
Q

increasing the extracellular conc of K+ by a factor of 5x will cause..

A

depolarization (influx of Na+)

37
Q

graded potentials dissipate..

A

within a few mms

38
Q

local anesthetics block..

A

voltage-gated sodium channels

39
Q

propagation of APs is necessary for the AP to travel over a few mms because

A

the resistance of axoplasm to the flow of ions is very high

40
Q

demyelination of peripheral nerve fibers causes APs to have..

A

a decreased conduction velocity