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MSK exam 2 AP > Action Potentials > Flashcards

Action Potentials Flashcards

1
Q

leak channels

A

always open

unregulated ion movement in one direction of electrochemical gradient

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2
Q

gated channels

A

slide 5

typically ion specific

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3
Q

depolarization

A 
flow of (+) ions into cell 	
(membrane potential becomes less negative)
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4
Q

repolarization

A 
flow of (+) ions out of cell (potassium)
brings back to resting membrane potential
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5
Q

-90 mV

A

resting membrane potential

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6
Q

0 mV

A

overshoot phase

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7
Q

what increases membrane excitability

A

when membrane becomes more POSITIVE (closer to threshold)

closer to threshold means closer to excitability

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8
Q

an increase in EC potassium (K+) concentration would lead to the membrane becoming….

A

more excitable!

potassium is high in the cell and retains its positive charge inside the cell

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9
Q

K+ ions moving out of the cell?

A

will be the repolarization stage of the action potential

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10
Q

Ungated K+ channels

A

always open

K+ efflux (until Ek+ is reached)

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11
Q

3 states of voltage gated sodium channels?

A

Closed but capable of opening (-70)

Open (activated) (-50 mV to +30 mV)

Closed and not capable of opening (inactivated) (+30 mV to -70 mV (ball and chain)

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12
Q

Two states of potassium gated channels?

A

closed but capable of opening

open from peak potential through after hyperpolarization

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13
Q

when do K voltage gated channels open?

A

slowly!

open around peak of the action potential

potassium will be leaving the cell for repolarization phase

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14
Q

how is the action potential generated?

A

by the rapid opening and subsequent voltage inactivation of voltage-dependent Na+ channels and the delayed opening and closing of voltage-dependent K+ channels.

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15
Q

what happens when Na+ ions move into the cell?

A

the membrane becomes depolarized into the positive direction

-occurs at more negative membrane voltages
versus the potassium which occurs at more positive membrane voltages

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16
Q

if the duration of the stimulus is short….

A

the intensity must be high1

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17
Q

if the duration of the stimulus is long….

A

a lower intensity stimulus can trigger an action potential

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18
Q

phases of depolarization

A

initial depolarization (reaches threshold)

Na+ channels open

Na+ influx (depolarizes)

Peak Na+ conductance

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19
Q

repolarization phases

A

early depolarization (voltage gated Na channels close and lock AND voltage gated K channels are still opening)

K+ efflux (repolarizes membrane in direction of Ek+)

Peak K + conductance

slide 20

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20
Q

what would happen if voltage gated K+ channels didn’t open?

A

it would eventually get back down to rest (b/c of leak channels) BUT it would take much longer

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21
Q

Refractory period

A

Time period after AP when a subsequent AP either cannot, or likely will not, be generated

Key for ensuring unidirectional propagation of APs

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22
Q

absolute refractory

A

no matter how large the next stimulus you are still NOT going to get another AP b/c of the inactivation gates of voltage gated Na channels

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23
Q

relative refractory

A

another AP can be produced only if the stimulus is large enough (stronger than normal)

directly related to delay or slower gating kinetics of voltage gated K channels (delayed closing of K+ voltage gated channels)

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24
Q

Why do we have refractory periods? x2

A

ensures unidirectional propagation

set upper limit to AP firing frequency

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25
AP potential characteristics
undiminshed propagation All-or-none law
26
if stimulus is greater than required to reach threshold...
AP is still same size cannot sum AP's
27
nervous system does not differentiate intensity of stimulus by size of AP but rather....
by AP frequency and/or number of AP's
28
Graded potential
less than threshold (SUB THRESHOLd) usually produced by Na+ influx change in potential can vary (duration and strength is directly proportional to duration and strength of stimulus) spread by passive current flow DECREMENTAL- not propagated and can die out resistance hinders flow CAN BE SUMMATED
29
do graded potentials have refractory period?
NO b/c they are sub threshold
30
Decremental current flow? what is that
not propagated die out over short distances resistance hinders flow of electrical current (V=IR)
31
differences b/w graded and action potentials
slide 31
32
dendrites
signal toward cell body
33
axon
signal away from soma
34
axon hillock
initial segment lowest threshold for AP initiation
35
which characteristic of an axon is most dependent on diameter?
conduction velocity of action potentials
36
Conduction methods (x2)
Contiguous saltatory
37
contiguous conduction
Local event of reaching threshold causes enough Na+ influx to open adjacent channels → more Na+ flows into adjacent channels........down entire length of membrane Positive-feedback entire membrane has been depolarized & repolarized an AP is conducted then it triggers neighboring AP and so and so on.... so one AP doesn't travel all the way down, there are multiple AP's
38
saltatory conduction
Property of MYELINATED nerve fibers which increases conduction velocity Nodes of Ranvier (not myelinated): Concentrated Na+ channel expression Impulse “jumps” between nodes down the length of the axon increases conduction velocity up to 50x faster
39
Myelin function
insulating resistance high trans-membrane resistance to internode region forces current to travel node to node where there is lower resistance
40
Axon diameter effects what?
increase in axon diameter actually increases axon potential propagation larger diameter --> decreased internal resistance to current flow
41
what increases conduction velocity
myelination increased axon diameter
42
2 types of synaptic communication
electrical synapses chemical synapses
43
electrical synapses
allow for direct communication of electrical signal from cell to cell gap junctions (which have connexon channels) low-resistance to current flow
44
chemical synapses
unidirectional signal transmission | electrical signal --> chemical signal
45
ionotropic
slide 44
46
metabotropic
slide 44
47
voltage gated calcium channels
are expressed at synaptic terminal of pre-synaptic neuron can tell when AP is coming in capable of responding to depolarzing stimulus (by opening up--> calcium influx) 10,000:1 Ca outside to inside of cell
48
convergance
multiple synapses on one postsynaptic cell body | sensory neurons such as feedback coming back to spinal cord
49
divergance
branching axon terminals can affect thousands of postsynaptic cells (Ex: motor neuron → multiple fibers of motor unit)
50
prior to axon hillock what type of potentials?
graded
51
what does the axon hillock possess that allows it to transmit/make AP?
high concentration of voltage-gated Na+ channels
52
how does the neuron decide what to transmit?
tally the votes of EPSP's and IPSP's
53
excitatory synapse
depolarizes/hypopolarizes always excitatory EPSP- subthreshold event bringing membrane closer to threshold
54
inhibitory synapse
IPSP hyperpolarizes membrane (says no don't do it) this is always inhibitory
55
how to get an EPSP?
Na influx or K efflux
56
how to get an IPSP?
Potassium efflux Cl influx
57
spatial summation
EPSP's initiated simultaneously allowing threshold to be reached and AP to be generated
58
temporal summation
if an excitatory presynaptic input is stimulated a second time before the first EPSP has died off, the second EPSP will add onto, or sum with the first EPSP, resulting in temporal summation
59
EPSP-IPSP cancellation
activation of ex1 and inn 1 presynaptic input does not change the postsynaptic potential b/c these two results (EPSP and IPSP) cancel each other out
60
look at supplemental summary posted after lecture
do it
61
hypocalcemia
hyperexcitability/spontaneous muscle twitch decreased threshold voltage of Na channel gating reach threshold at a lower potential than normal
62
hypercalcemia
when EC of calcium is elevated it can lead to hypo excitability/muscle weakness decreased membrane excitability
63
K + has what effect usually?
inhibitory role in excitatory cells due to very negative equilibrium potential

MSK exam 2 AP (7 decks)

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