Membrane Depolarization & AP

Question 1

If AP will be propagated by postsynaptic cell depends on?

Answer 1

1. Stimulus number
2. Stimulus magnitude
3. Stimulus nature (EPSP/IPSP)
4. Stimulus locale (axon hillock → this is important)

Question 2

Permeability is the same as?

Answer 2

Conductance

Question 3

Steps of Nt-stimulated ion current

Answer 3

1. Nt causes local increase in Vmem
2. Change in Vmem permits flow of ionic current
3. Local current flow leads to depolarization of small area of membrane
4. Area of depolarization may grow

Question 4

The area of depolarization will grow IF:

Answer 4

1. V-sensitive channels are present

2. Depolarization is of sufficient magnitude

Question 5

How does flow of current affect depolarization magnitude?

Answer 5

Greater flow of current → greater magnitude of depolarization

Question 6

How does flow of current affect area of depolarization?

Answer 6

Greater current flow → larger area of depolarization

Question 7

Length constant provides an indication of?

Answer 7

Area that will be affected

Question 8

Bigger length constant = ?

Answer 8

Bigger area affected

Question 9

If 2 cells receive the same stimulus, which will have a larger area of depolarization?

Answer 9

One with longer length constant

Question 10

Decremental conduction

Answer 10

Not sustained over time → as it gets farther from the stimulation site, it gets smaller

Question 11

What is (positive) spatial summation of non-propagating depolarization?

Answer 11

Overlapping zones of depol. construnctively reinforce one another → results in greater depolarization in area of overlap

Question 12

For an AP to be propagated, the zone of depol. must include?

Answer 12

Axon hillock

Question 13

What is destructive spatial summation?

Answer 13

Overlapping zones of depol. and high Cl- conductance destructively reinforce on another → results in reduced propagation of depolarization

Question 14

What is temporal summation?

Answer 14

Stimulations close in time build on one another

Question 15

How long does it take V-sensitive Na channels to deactivate?

Question 16

What are the two conductance components of AP?

Answer 16

PNa and PK

Question 17

E(m) is the weighted average of?

Answer 17

E(Na) and E(k)

Question 18

What is the weighting factor for E(m)?

Answer 18

Relative conductance of Na and K

Question 19

Magnitude of depolarization at any point depends on?

Answer 19

1. Magnitude of depolarization at source (current density)

2. Distance from source

Question 20

Electrotonic depolarization does not depend on?

Answer 20

Activation of V-sensitive channels

Question 21

What does electrotonic depolarization do?

Answer 21

Changes distrubtion of charge to change membrane polarization without change in conductance

Question 22

What is the final site of integration (logic gate of cell)?

Answer 22

Axon hillock

Question 23

Where is the highest density of Na(V) channels?

Answer 23

Axon hillock

Question 24

Types of channels at axon hillock?

Answer 24

1. Na(V)
2. K(V)
3. Ca(V)
4. K(Ca)

Question 25

Absolute refractory period

Answer 25

Most Na(V) channels are activated or inactivated → ARP cannot occur

Question 26

Relative refractory period

Answer 26

Membrane is hyperpolarized → requires stronger than normal stimuli

Question 27

What prevents AP from moving retrograde?

Answer 27

Refractory period

Question 28

Length constant depends on?

Answer 28

Ratio of membrane resistance to cytoplasmic resistance

Question 29

How can cell increase length constant?

Answer 29

1. Decrease cytosolic resistance

2. Increase membrane resistance

Question 30

How can cell decrease cytosolic resistance?

Answer 30

Increase diameter

Question 31

How can cell increase membrane resistance?

Answer 31

Myelination

Question 32

Which is more effective, increased axon size or myelination?

Answer 32

Myelination