MCP 27: Ion Channels and Action Potentials

Question 1

threshold

Answer 1

voltage at which action potential starts, usually around -50mV

Question 2

overshoot

Answer 2

how much greater than zero the action potential goes

Question 3

undershoot

Answer 3

how much under the resting potential the action potential goes, because K+ channels remain open for a longer time

Question 4

tetrodotoxin (TTX)

Answer 4

blocks the fast voltage-gated sodium channels

Question 5

voltage clamp

Answer 5

keeps voltage constant and you can measure the current even when conductance is changing, any change in current is a result from a change in conductance (G); gives data on CONDUCTANCE CHANGES OVER TIME!

Question 6

current clamp

Answer 6

keeps current constant

Question 7

features of potassium channels

Answer 7

slow to open, do not inactivate, responsible for outward current of action potential

Question 8

Tetraethylammonium (TEA)

Answer 8

blocks potassium channels

Question 9

features of sodium channels

Answer 9

activate super fast, inactivates super fast, responsible for inward current, when you get to higher voltages, reverses direction

Question 10

patch clamp experiment

Answer 10

can hold the voltage of a single ion channel constant and measure the current

Question 11

relative refractory period

Answer 11

possible to get an action potential because Na+ channels have reactivated, but need stronger stimulus; because K+ channels do not deactivate and are causing hyperpolarization

Question 12

absolute refractory

Answer 12

time when you cannot get an action potential because Na+ channels have deactivated

Question 13

current moving backwards

Answer 13

doesn’t happen because Na+ are deactivated, unless you start an action potential in the middle of the axon

Question 14

conduction velocity

Answer 14

speed of action potential measured in meters/second; depends on internal diameter of axon, internal resistance, membrane capacitance, myleination, activation kinetics of the Na+ channel

Question 15

passive property of cables

Answer 15

when you apply a current to a cable, the voltage decreases with increasing distance

Question 16

threshold

Answer 16

when the influx of sodium from the voltage gated channels is large enough to counterbalance the current produced by the K+ leakage channel, explosive action potential occurs

Question 17

space constant

Answer 17

distance it takes for the action potential to fall to 37% of its original strength, increasing membrane resistance and axon diameter both increase space constant and allow action potential to travel farther. space constant=sqrt(Rm/Ri) where Ri=1/d

Question 18

diameter of axon

Answer 18

decrease internal resistance, increase space constant, and internal velocity

Question 19

role of calcium

Answer 19

higher Ca+2=decreased excitability, lower Ca+2=increased excitability; alters the way Na+ channels sense membrane potential because of shielding effects on the voltage sensor

Question 20

hyperkalemic periodic paralysis or paramyotonia congenita

Answer 20

amino acid mutation in sequence encoding Na+ channel

Question 21

cocaine

Answer 21

sodium channel blocker–other drugs ending in -aine

Question 22

myelination

Answer 22

increases resistance and decreases capacitance

Question 23

time constant

Answer 23

gives a measure of the speed of charging a capacitor, at t=tau, the charge on an initially uncharged capacitor is 63% its maximum value; on a fully charged capacitor, the charge q on the capacitor decreases exponentially with time depending on the rate constant. At time t=tau, the charge on the capacitor is reduced to 37% its original value. tau=Rm X Cm

Question 24

capacitance

Answer 24

steals charge from the action potential

Question 25

inward negative current

Answer 25

positive ions flowing into the cell

Question 26

saxitoxin

Answer 26

blocks sodium channels

Question 27

peak of action potential

Answer 27

Na+ channels deactivate, K+ leakage channels allow for some repolarization, delayed voltage-gated K+ channels activate and allow huge flux of K+ out of the cell

Question 28

Nodes of Ranvier

Answer 28

block AP from occurring bc of myelin–AP can only happen at nodes (http://www.wisegeek.com/what-are-nodes-of-ranvier.htm#didyouknowout)