Neuronal Action Potentials

Question 1

action potential propagation

Answer 1

• propagated without degradation

Question 2

propagation without degradation important for

Answer 2

• communication over long distances

Question 3

conduction velocity of myelinated axons versus unmyelinated axons

Answer 3

• myelinated axons have a faster conduction velocity

Question 4

conduction velocity of large-diameter axons

Answer 4

• faster conduction velocity than small diameter axons

Question 5

the spatial distribution and density of specific types of ion channels influences

Answer 5

• the site of initiation of the action potentials

- the modulation of action potentials

Question 6

all or none phenomenon

Answer 6

• once triggered, an action potential is a consistent amplitude and duration

Question 7

what is the voltage required to get enough voltage to open or initiate the all-or-none behavior of the action potential

Answer 7

• threshold

Question 8

a sub threshold stimulus fails to do what

Answer 8

• fire an action potential

Question 9

small depolarizations due to

Answer 9

• opening of ligand gated or stimulus gated channels

Question 10

if the depolarization is large enough

Answer 10

• then voltage gated Na+ channels open

Question 11

depolarization phase on the graph

Answer 11

• upstroke

Question 12

local depolarization causes opening of

Answer 12

• Na+ voltage gated channels
• Na+ influx
• full depolarization

Question 13

overshoot on graph

Answer 13

• depolarization above 0 mV

Question 14

repolarization on graph

Answer 14

• going from overshoot down toward resting potential

Question 15

what happens during repolarization to the Na+ voltage gated channel

Answer 15

• will be inactivated

Question 16

rate of sodium channel

Answer 16

• open and inactivate rapidly

Question 17

rate of potassium channel

Answer 17

• open and close slowly

Question 18

what is the result of slow closure of potassium channels?

Answer 18

• the hyper polarization phase

Question 19

repolarization of the membrane potential occurs due to

Answer 19

• inactivation of voltage gated Na+ channels

- opening of voltage gated K+ channels

Question 20

Na+/K+ ATPase function

Answer 20

• restore the ionic gradients

Question 21

the movement of what is responsible for the action potential

Answer 21

• movement of only a few ion molecules

Question 22

does the intracellular or extracellular concentration of an ion really change at the peak of an action potential?

Answer 22

• not really

Question 23

absolute refractory period is when

Answer 23

• all Na+ channels are open or inactivated

Question 24

relative refractory period is when

Answer 24

• K+ permeability is elevated and some Na channels are still inactivated

Question 25

the refractory zone results in

Answer 25

• propagation of action potentials in one direction

Question 26

myelin is

Answer 26

• concentric wraps of lipid-rich glial cell processes

Question 27

myelin surrounds

Answer 27

• axons

Question 28

what myelinate axons in the peripheral nervous system

Answer 28

• Schwann cells

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Question 29

what myelinate axons in the central nervous system

Answer 29

• oligodendrocytes

Question 30

wraps of myelin do what

Answer 30

• increase resistance of membrane resulting in less leakage of current out of the axon

Question 31

myelination and speed of conduction of action potential

Answer 31

• myelination increases the speed of conduction of the action potential up to 50 times faster along the length of the axons

Question 32

saltatory conduction

Answer 32

• wave of depolarization in a myelinated axon jumps for node of Ranvier to the next node of Ranvier

Question 33

why do unmyelinated axons conduct action potentials more slowly

Answer 33

• due to current leaking out of cell into the ECF

Question 34

larger diameter axons tend to be

Answer 34

• myelinated

Question 35

the larger the diameter (in regard to wrapping of myelin)

Answer 35

• the greater the wrapping of myelin

Question 36

small diameter axons tend to be

Answer 36

• thinly myelinated

- unmyelinated

Question 37

which are the slowest conducting axons

Answer 37

• small diameter, unmyelinated axons

Question 38

what is the initiation site for action potentials

why

Answer 38

• axon hillock

- voltage gated Na+ highly concentrated here

Question 39

where are voltage gated Na+ channels also highly concentrated?

Answer 39

• nodes of Ranvier