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
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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
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