Action Potentials 1

Question 1

resting phase

Answer 1

Na+ ions more numerous outside of membrane
K+ ions more numerous inside membrane
positive charge outside and negative charge inside
Established by the sodium-potassium pump

Question 2

sodium potassium pump

Answer 2

Sodium-potassium pump pumps 3 Na+ ions out of cell for every 2 K+ ions it pumps into the cell

Question 3

Resting membrane potential

Answer 3

= -70 mV

Question 4

na+/k+ pump

Answer 4

K+ ions can leak through membrane through ion channels; Na+ cannot because its ion channels are closed

Question 5

polarized resting potential

Answer 5

neuron more negatively charged inside than outside

Question 6

excitatory signals

Answer 6

cause threshold to be reached and action potential to fire

Question 7

inhibitory signals

Answer 7

inhibit action potential from firing

Question 8

threshold

Answer 8

-55 mV

Question 9

absolute refractory period

Answer 9

the period of time after an action potential is initiated in which it’s impossible to initiate another action potential
1 msec

Question 10

spike initiation zone

Answer 10

part of neuron where axon originates from soma

axon hillock

Question 11

voltage at resting potential

Answer 11

-70 mV

Question 12

voltage to reach threshold

Answer 12

-55 mV

Question 13

structure of voltage gated sodium channel

Answer 13

four domains with each six transmembrane alpha helices
four domains clump together to form pore, closed at negative resting potential
selectivity filter that makes it permeable to na+ but not k+
ion-water complex

Question 14

what causes sodium channels to open

Answer 14

depolarization twists s4 after entire segment is forced to move by changing membrane potential
conformational change causes gates to open
membrane potential from -65 to -40

Question 15

what causes potassium channels to open

Answer 15

when membrane is depolarized and functions to diminish any further depolarization by giving k+ ions a path to leave the cell across the membrane

Question 16

what happens when potassium channels open

Answer 16

k+ ions flow out of cell, down concentration gradient, until inside is negative
electrical current created
Vm = Ek

Question 17

relative refractory period

Answer 17

period after end of absolute refractory period
relatively difficult to initiate another action potential (several msecs)
amount of current required to depolarize neuron to action potential threshold elevated above normal

Question 18

why is it important for cell to repolarize and return quickly to resting potential

Answer 18

so cell is prepared to generate another action potential as soon as it needs to

Question 19

what happens to axons in multiple sclerosis

how does this impact message transmission

Answer 19

MS attacks myelin sheaths of bundles of axons in brain, spinal cord, and optic nerves
slows message transmission

Question 20

how do local anesthetics stop you from feeling pain during surgery

Answer 20

temporarily block action potentials in axons, especially small ones
some bind to voltage gated sodium channels and interfere with flow of na+ that normally results from depolarizing channel

Question 21

what determines whether or not to fire action potential

Answer 21

cell body

Question 22

APs direction

Answer 22

can only travel in one direction because of inactivated sodium channels

Question 23

local anesthetic ex

Answer 23

novacaine

Question 24

na+ have what as chaperone

Answer 24

water molecule

Question 25

ttx affects

Answer 25

na+ channel