SDL: Action Potential

Question 1

the resting membrane potential

Answer 1

-70 mV

Question 2

the phases of the action potential

Answer 2

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

Question 3

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

Answer 3

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

Question 4

the large increase in permeability of Na+ allows for

Answer 4

a large Na+ inward current (depolarization)

Question 5

the equilibrium potential for Na+

Answer 5

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

Question 6

what happens to ion channels at the threshold potential?

Answer 6

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

Question 7

the 2 gates that Na+ channels have

Answer 7

activation/deactivation gate + inactivation/deinactivation fate

Question 8

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

Answer 8

OUT of the cell

Question 9

the resulting efflux of K+ causes which phase?

Answer 9

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

Question 10

effects of tetrodotoxin

Answer 10

blocks voltage-gated Na+ channels

Question 11

effects of tetraethylammonium ions

Answer 11

block voltage-gated K+ channels

Question 12

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

Answer 12

a system that regenerates the action potential along the axon

Question 13

what causes eddy currents?

Answer 13

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

Question 14

what is saltatory conduction?

Answer 14

when the AP skips from node to node on myelinated axons

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

what is the absolute refractory period?

Answer 17

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

Question 18

what is the relative refractory period?

Answer 18

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

Question 19

what is the subnormal period?

Answer 19

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)

Question 20

what is orthodromic conduction?

Answer 20

normal conduction direction from the AP, away from the soma

Question 21

what is antidromic conduction?

Answer 21

conduction of AP toward the soma

Question 22

what is an electrotonic/graded potential?

Answer 22

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

Question 23

what are examples of the normally occurring electrotonic potentials?

Answer 23

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

Question 24

how can neuropathy be tested for?

Answer 24

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).

Question 25

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..

Answer 25

depolarized

Question 26

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

Answer 26

hyperpolarized

Question 27

example of mechanical pressure changing ions across the membrane

Answer 27

striking the "funny bone"

Question 28

neuropathy is caused by

Answer 28

unhealthy nerve fiber with slowed conduction velocity

Question 29

what is depolarization block? what causes it?

Answer 29

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

Question 30

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

Answer 30

4 minutes

Question 31

describe what is happening when limbs "go to sleep"

Answer 31

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

Question 32

what is hyperpolarization block?

Answer 32

when the MP is maintained below the resting potential level

Question 33

drugs/events that cause hyperpolarization block

Answer 33

novocaine, lidocaine, hypoxia

Question 34

what do local anesthetics block?

Answer 34

voltage-gated Na+ channels

Question 35

what happens in an injury current?

Answer 35

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

Question 36

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

Answer 36

depolarization (influx of Na+)

Question 37

graded potentials dissipate..

Answer 37

within a few mms

Question 38

local anesthetics block..

Answer 38

voltage-gated sodium channels

Question 39

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

Answer 39

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

Question 40

demyelination of peripheral nerve fibers causes APs to have..

Answer 40

a decreased conduction velocity