Week 3-Action Potentials Flashcards Preview

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Flashcards in Week 3-Action Potentials Deck (42)
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1

Action Potential

1. large depolarizing wave
2. actively propagates down axon
3. & does not lose amplitude

2

potential sensitive channels (voltage gated)

open and close in response to Vm

3

Depolarization

opens V-Na+
-->Na+ rushes into cell
-->MORE depolarization

4

hyperpolarization

V-K+ open
-->K+ rushes out of cell
-->hyperpolarization

5

Voltage clamp

1. measures Vm
2. changes Vm to any determined value
3. adds current to either side of membrane to this Vm
-->breaks feed forward process of V-gated channels
(Na+ doesn't cause more depolarization)

6

Threshold (Vt)

value of Vm when net ionic current changes from outward to inward

7

Tetrodotoxin (TTX)

binds/clogs V-Na+
-only V-K+ functional

8

Tetrathylammonium (TEA)

binds/clogs V-K+
-only V-Na+ functional

9

V-gates similarities

1. both open to depolarization
2. both have a greater response to greater depolarization
3. have inactivation protein to close channels

10

V-gates differences

1. Na+ open more rapidly than K+
2. If depolarization persists, Na+ close, K+ do not
3. Na+ channels faster to close than K+
*individual gates have different thresholds

11

V-Na+ channels states

1. closed-ready for opening
2. open
3. closed-refractory

12

Refractory period

brief period following AP
-cannot fire again
-closed state of Na+ channels

13

Absolute refractory

immediately following AP
-neuron cannot fire b/c all Na+ channels locked/closed

14

Relative refractory

right after absolute refractory
-AP can be fired only if stimulus is stronger than usual
-Na+ channels that become ready have different thresholds

15

Accomodation

*does not happen in nature
-when slow depolarization raises Vm well passed normally observed threshold before generating AP
-due to hyperpolarization of K+ channels keeping up with slow depolarization of Na+ channels

16

Direction of AP

axon hillock-->axon terminal
1. axon hillock: lowest threshold to fire over any part of an axon
2. refractory period of Na+ channels

17

After potential

AP followed by hyperpolarization
-->slowness of V-K+ channels to close after activation

18

4 types of V-K+ channels

1. slowly activated
2. Ca++ activated K+ channel opens to depolarization by voltage sensitivity depends on intracellular Ca++
3. A-type: fast, transient activated by depolarization
4. M-type: activated by depolarization but inactivated by ACh

19

V-Ca++

at rest-Ca++ intracellular concentrations very low
1. Ca++ pump: buffering system (very slow)
-Ca++ comes in after 1 AP can exceed capacities and begins to accumulate
2. Series of AP--> increase Ca++ in cell
-increase probability of opening Ca+ activated K+ channels
-hyperpolarization
3. some Ca++ channels sensitive to intraneuronal Ca++
-binds to internal surface of channels to close them

20

Ca++ influx

1. contribute directly to depolarization of AP
2. contributes to hyperpolarization of AP
-Ca++ influx activates K+ channels
-Ca++ decrease own influx by blocking own channels

21

Ca++ & PSP

-decrease extracellular Ca++ will block PSP
-increase extracellular Ca++ increases PSP
*more Ca++ = greater PSP

22

location of V-Ca++ channels

only at axon terminal-->opens with depolarization

23

V-Ca++ channel types

1. L-type
2. P/Q type
3. N type
4. R type
5. T type

24

N-type V-Ca++

FAST
associated with exocytosis & release of NT

25

L-type V-Ca++

SLOW
not localized in areas of NTs
involved in neuropeptide release & vesicle mobilization

26

Miniature end plate potentials

result of vesicles dumping NT contents into synapse

27

del Castillo/Katz hypothesis

1. normal conditions: end plate potential of ~70 mV
-due to about 150 vesicles dumping into synapse
2. variations of end plate potentials = results of varying amounts of vesicles dumping

28

Dense bars

located directly opposite post synaptic receptor sites
-vesicles collect in rows along dense bar
dense bars + vesicles = ACTIVE ZONE

29

Active zone

dense bars + vesicles
where NT release occurs

30

Exocytosis

process whereby vesicles release NT into synapse
-pore on vesicle matches axon terminal membrane pore
*N-type Ca++ channels