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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
Q

AP potential characteristics

A

undiminshed propagation

All-or-none law

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26
Q

if stimulus is greater than required to reach threshold…

A

AP is still same size

cannot sum AP’s

27
Q

nervous system does not differentiate intensity of stimulus by size of AP but rather….

A

by AP frequency and/or number of AP’s

28
Q

Graded potential

A

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
Q

do graded potentials have refractory period?

A

NO b/c they are sub threshold

30
Q

Decremental current flow? what is that

A

not propagated

die out over short distances

resistance hinders flow of electrical current (V=IR)

31
Q

differences b/w graded and action potentials

A

slide 31

32
Q

dendrites

A

signal toward cell body

33
Q

axon

A

signal away from soma

34
Q

axon hillock

A

initial segment

lowest threshold for AP initiation

35
Q

which characteristic of an axon is most dependent on diameter?

A

conduction velocity of action potentials

36
Q

Conduction methods (x2)

A

Contiguous

saltatory

37
Q

contiguous conduction

A

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
Q

saltatory conduction

A

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
Q

Myelin function

A

insulating resistance

high trans-membrane resistance to internode region

forces current to travel node to node where there is lower resistance

40
Q

Axon diameter effects what?

A

increase in axon diameter actually increases axon potential propagation

larger diameter –> decreased internal resistance to current flow

41
Q

what increases conduction velocity

A

myelination

increased axon diameter

42
Q

2 types of synaptic communication

A

electrical synapses

chemical synapses

43
Q

electrical synapses

A

allow for direct communication of electrical signal from cell to cell

gap junctions (which have connexon channels)

low-resistance to current flow

44
Q

chemical synapses

A

unidirectional signal transmission

electrical signal –> chemical signal

45
Q

ionotropic

A

slide 44

46
Q

metabotropic

A

slide 44

47
Q

voltage gated calcium channels

A

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
Q

convergance

A

multiple synapses on one postsynaptic cell body

sensory neurons such as feedback coming back to spinal cord

49
Q

divergance

A

branching axon terminals can affect thousands of postsynaptic cells

(Ex: motor neuron → multiple fibers of motor unit)

50
Q

prior to axon hillock what type of potentials?

A

graded

51
Q

what does the axon hillock possess that allows it to transmit/make AP?

A

high concentration of voltage-gated Na+ channels

52
Q

how does the neuron decide what to transmit?

A

tally the votes of EPSP’s and IPSP’s

53
Q

excitatory synapse

A

depolarizes/hypopolarizes

always excitatory

EPSP- subthreshold event bringing membrane closer to threshold

54
Q

inhibitory synapse

A

IPSP

hyperpolarizes membrane (says no don’t do it)

this is always inhibitory

55
Q

how to get an EPSP?

A

Na influx or K efflux

56
Q

how to get an IPSP?

A

Potassium efflux

Cl influx

57
Q

spatial summation

A

EPSP’s initiated simultaneously allowing threshold to be reached and AP to be generated

58
Q

temporal summation

A

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
Q

EPSP-IPSP cancellation

A

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
Q

look at supplemental summary posted after lecture

A

do it

61
Q

hypocalcemia

A

hyperexcitability/spontaneous muscle twitch

decreased threshold voltage of Na channel gating
reach threshold at a lower potential than normal

62
Q

hypercalcemia

A

when EC of calcium is elevated it can lead to hypo excitability/muscle weakness

decreased membrane excitability

63
Q

K + has what effect usually?

A

inhibitory role in excitatory cells due to very negative equilibrium potential

MSK exam 2 AP (7 decks)

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