Lecture 3

Question 1

Action Potential?

Answer 1

Rapid + transient change in the membrane potential (Vm) of a cell (ex. neuron)

Question 2

Basis of electrical signaling in body?

Answer 2

Action Potential

Question 3

Action Potentials usually initiate at?

Answer 3

Axon Hillock

Question 4

Action Potentials are propagated by?

Answer 4

Voltage-Gated Ion Channels along the axon

Question 5

Action Potential is an _____ phenomenon?

Answer 5

“All-or-Nothing”

Question 6

AP will NOT fire if Vm is?

Answer 6

Under threshold

Question 7

Minimum depolarization needed to?

Answer 7

Fire AP

Question 8

S4 segment senses change in?

Answer 8

Voltage

Question 9

“Voltage Sensors” with Ion Selectivity?

Answer 9

1) Na+ Channel
2) K+ Channel (Tetramer)

Question 10

Voltage-Gated Na+ Channels?

Answer 10

3 Conformational States (Open, Inactivated, Closed)

Question 11

Activation of the voltage-gated Na+ channels leads to?

Answer 11

Increased flow of ions and depolarization

Question 12

Inactivation of the voltage-gated Na+ channels leads to?

Answer 12

Stops the flow of ions and leads to repolarization

Question 13

Voltage-Gated K+ Channels?

Answer 13

1) Depolarization triggers opening of voltage-gated K+ channels
2) K+ ions rush OUT OF cell
3) Transient efflux (high Pk) leads to Hyperpolarization

Question 14

Depolarization triggers?

Answer 14

Opening of Voltage-Gated K+ channels

Question 15

Hyperpolarization is built in defense against?

Answer 15

Hyperexcitability (Negative feedback decreases probability of activating more channels)

Question 16

Na+ and K+ Channel Synchrony?

Answer 16

1) Rapid activation of Na+ channels causes depolarization
2) Na+ channel inactivation STOPS depolarization
3) Slower activation of K+ channels contributes to depolarization and eventual hyperpolarization

Question 17

Propagation?

Answer 17

Movement down axon

Question 18

Non-Propagated Depolarization?

Answer 18

Spreads passively through local current flow (“Electronic Conduction”)

Question 19

Depolarization attenuates as it?

Answer 19

Moves down axon

Question 20

Peak membrane potential during an AP remains?

Answer 20

Consistently depolarized

Question 21

AP propagation takes?

Answer 21

Time (to charge membrane)

Question 22

Myelination increases?

Answer 22

Conduction velocity

Question 23

Depolarization decreases as it?

Answer 23

Moves down axon

Question 24

Propagated Depolarization (Concept 1)?

Answer 24

Depolarization attenuates as it moves down axon

Question 25

Propagated Depolarization (Concept 1) is caused by?

Answer 25

1) Membrane Resistance (Rm) 2) Interaxonal Resistance (Ri)

Question 26

Membrane Resistance?

Answer 26

Barricade on cell surface that is preventing passive flow of ions out

Question 27

Interaxonal Resistance?

Answer 27

Resistance inside axon ("like traffic")

Question 28

Length Constant?

Answer 28

Distance it takes to reach 37% of Vmax

Question 29

Length Constant is directly proportional to?

Answer 29

Rm

Question 30

Length Constant is inversely proportional to?

Answer 30

Ri

Question 31

Propagated Depolarization (Concept 2)?

Answer 31

Peak membrane potential along an axon during an AP remains consistently depolarized

Question 32

Propagated Depolarization (Concept 2) is caused by?

Answer 32

Refractory Periods

Question 33

Refractory Periods keep it?

Answer 33

Moving down the axon

Question 34

Absolute Refractory Period?

Answer 34

A 2nd Ap can NOT fire (Na+ channels can not be reactivated) (either in open or inactivated state)

Question 35

Relative Refractory Period?

Answer 35

A much greater depolarization required for an AP to fire (Active K+ channels hyperpolarizing the cell)

Question 36

Propagated Depolarization (Concept 3)?

Answer 36

AP propagation takes time (time is needed for the membrane to charge as the AP moves along the axon)

Question 37

Time needed to charge membrane = ?

Answer 37

Rate limiting event of AP propagation

Question 38

Time Constant?

Answer 38

Time it takes for the change in Vm to reach 63% of its final value

Question 39

Time Constant is directly proportional to?

Answer 39

Rm

Question 40

Time Constant is directly proportional to?

Answer 40

Cm

Question 41

Greater the size of the axon?

Answer 41

Greater the time it takes for the membrane to charge

Question 42

Capacitance?

Answer 42

Ability for something to hold a charge

Question 43

Propagated Depolarization (Concept 4)?

Answer 43

Myelination increases the conduction velocity by: 1) Increasing Rm --> Increases length constant 2) Decreasing Cm --> Decreases time constant

Question 44

Myelination increase = ?

Answer 44

Membrane Resistance will increase

Question 45

Saltatory Conduction?

Answer 45

Propagation of APs along myelinated axons from 1 node of Ranvier to the next node

Question 46

Multiple Sclerosis?

Answer 46

An autoimmune, degenerative disease of axon demyelination

Question 47

MS increases?

Answer 47

Passive current flow

Question 48

MS decreases?

Answer 48

AP conduction velocity

Question 49

MS results in?

Answer 49

Muscle Functions being messed up