Lecture 3 (Revised)

Question 1

Action Potential is a?

Answer 1

Rapid + transient change in membrane potential (Vm) of a cell (ex. neuron)
(basis of electrical signaling in body)

Question 2

AP usually initiate at?

Answer 2

Axon Hillock

Question 3

AP usually propagated by?

Answer 3

Voltage-gated ion channels along axon

Question 4

“All-or-None” Phenomenon?

Answer 4

(Action Potential)
-Minimum depolarization needed to fire AP
-AP will NOT fire if Vm is under threshold
-Na+ channels blocked by TTX and Riluzole

Question 5

Voltage-gated Ion Channels?

Answer 5

“Voltage sensors” with ion selectivity
1) Na+ Channel
2) K+ Channel (Tetramer (4 subunits))
(S4 segment senses change in voltage)

Question 6

S4 segment?

Answer 6

Senses change in voltage and is what will change our ion channel from open to close

Question 6

Voltage-gated Na+ Channels?

Answer 6

-3 Conformational States:
1) Open (“a” or “m” gate)
2) Inactivated (“I’ or “h” gate)
3) Closed
-Activation (increased flow of ions (depolarization))
-Inactivation (stops flow of ions (repolarization))

Question 7

Voltage-gated K+ Channels?

Answer 7

1) Depolarization triggers opening of voltage-gated K+ channels
2) K+ ions rush OUT OF cell
3) Transient efflux (high Pk) leads to hyper polarization
-Hyperpolarization is built in defense against hyperexcitability (shooting another too soon)

Question 8

Negative feedback decreases probability of?

Answer 8

Activating more channels

Question 9

Na+ and K+ Channel Synchrony?

Answer 9

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

Question 9

Propagation means?

Answer 9

Movement down axon

Question 10

Non-Propagated Depolarization?

Answer 10

If minimum depolarization to reach threshold is not met, AP will not propagate, instead spreads passively through local current flow (“Electronic Conduction”)

Question 11

Key Concepts of AP Propagation?

Answer 11

1) Depolarization decreases as it moves down axon
2) Peak membrane potential during an AP remains consistently depolarized
3) AP propagation takes time (to charge membrane)
4) Myelination increases conduction velocity

Question 12

Propagated Depolarization (Concept 1)?

Answer 12

Depolarization decreases as it down axon, caused by:
1) Membrane resistance (Rm) (barricade on cell surface that is preventing passive flow of ions out)
2) Interaxonal resistance (Ri) (referring to resistance inside axon (like “traffic”))

Question 13

Length Constant?

Answer 13

Distance it takes to reach 37% of Vmax
-Directly proportional to Rm
-Inversely proportional to Ri

Question 14

Propagated Depolarization (Concept 2)?

Answer 14

Peak membrane potential along an axon during an AP remains consistently depolarized (caused by refractory periods)

Question 15

Absolute Refractory?

Answer 15

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

Question 16

Refractory Period makes sure AP?

Answer 16

Doesn’t stay in 1 spot

Question 17

Relative Refractory?

Answer 17

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

Question 17

Propagated Depolarization (Concept 3)?

Answer 17

AP propagation takes time
-Time is needed for membrane to charge
-Time needed to charge = rate limiting event of AP propagation

Question 18

Time Constant?

Answer 18

Time it takes for the charge in Vm to reach 63% of its final value
-Directly proportional to Rm
-Directly proportional to Cm

Question 19

Greater the size of the axon?

Answer 19

Greater the time it takes for membrane to charge

Question 20

Capacitance is?

Answer 20

Ability for something to hold a charge

Question 20

Time Constant Equation?

Answer 20

t = RmCm

Question 21

Propagated Depolarization (Concept 4)?

Answer 21

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

Question 22

Saltatory Conduction?

Answer 22

Propagation of EPs along myelinated axons from 1 node of Ranvier to next node

Question 23

Multiple Sclerosis?

Answer 23

An autoimmune, degenerative disease of axon demyelination
-Increases passive current flow
-Decreases AP conduction velocity

Question 24

Length Constant Equation?

Answer 24