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Neurosciences > Exam1Lec3ActionPotential > Flashcards

Exam1Lec3ActionPotential Flashcards

1
Q

What is action potential?

A

rapid, transient change in membbrane potential (Vm)

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2
Q

Na+ channel activation

A

responsible for transient inward current that depolarizes membrane

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3
Q

K+ channel activation

A

delayed activation responsible for delayed outward current that repolarizes the membrane

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4
Q

Threshold potential

A

Minimum depolarization required for an action potential to fire

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5
Q

Local current flow

A

action potential propagation along un-myelinated axon

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6
Q

Saltatory conduction

A

action potential propagation along myelinated axons. Much faster conduction

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7
Q

AP refractory period

A

time lag between action potentials

where ion channels rest b4 another ap can re-fiire

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8
Q

Multiple sclerosis

A

autoimmune, degenerative disease of axon demyelination
incr passive current flow
decr AP conduction velocity

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9
Q

Action potential usuaslly initiates in ____.

A

axon hillock

axon hillock= trigger zone

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10
Q

without ____ we don’t have an action potential

A

ATP

life is a neuron with a charge across membrane, and to get charge we need energy from ATP. So Na2+/K+ ATPase pumps establish and maintain membrane potential

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11
Q

What is EPSPS?

A

Makes Em more dep, and make is more likely to fire

driven glutamatergic transmission

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12
Q

What is IPSP?

A

Makes EM more hyperpolarized

driven by GABA

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13
Q

How can Em be changed?

slide 7
What triggers the physiological changes in membrane potential?

A

Changing internal or external ionic concentrations (usually K+)

changing relative perm of the ions across the plasma membrane

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14
Q

How are ionic permeabilities changed?

A
  1. Ligand gated (ex Gaba, glu, 5HT)
  2. Voltage-gated (Na+, K+)
  3. Nucleotide-gated (cAMP, cGMP)
  4. Inward rectifier “leak” channels
  5. Mechananosensitive-gated (stretch)
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15
Q

What are the 5 types of voltage gated ion channels?

A

Na+, Ca2+, K+, Cl-, H+

very sensitive to membrane potential

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16
Q

AP depolarization is triggered by transient opening of ____

A

Na+ channel

this always happens first and then we get a delay of K+ to hyperpolarization

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17
Q

mechanism of the voltage-gated Na+ channels

Na+ channels have 3 conformational states following a dep, what are they?

A

1st: open (a or m) gate state
2nd: inactive (I or H) gate
3rd: closed state

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18
Q

In the inactivation stage of Na+ what predominates?

A

Efflux of K+

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19
Q

K+ channel produes the delayed ____ current

A

outward

20
Q

How does K+ channel produes the delayed outward current?

A
  1. Dep triggers opening of voltage gated K+ channels
  2. K+ ions rush out of the cell
  3. K+ ions efflux causes a transient after hyperpolarization
  4. Pk remains high, causing Vm to be transiently more neg than baseline resting Vm (after hyperpol phase)

this is a built in system to prevent ap from firing too fast to prevent cell death

21
Q

What is an important component of the molecular structure of Na+ and K+ channels?

A

They have 4 subunits and the 4th one has a voltage sensing fxn with ion selectivity ( this dictates which ions can flow)

22
Q

Potassium channels are ____

A

tetramers (comprised of 4 identical subunits)

23
Q

____ segments “sense” changes in Vm, and move in response to these changes

A

S4

amino acids residues change in repsince to small mV differencees in voltage

24
Q

For a neuronal action potential we see a transient, rapid incr in ____ and a slower more stable increase in ____.

A

Pna, Pk

25
Q

Rapid activation of ____ channels causes depolarization

____ channel inactivation stops depolarization

Slower activation of ____ channels contributes to repolarization

A

Na+, Na+, K+

26
Q

Action potential waveforms vary in their shape. Why?

A

Because of differences in types of activated channels and their relative times of activity

depends on type of neuron

27
Q

Na+ channel activation enters a positive feedback loop, explain this

A

Na+ channel activation leads to a depolarization that incr probability of activation more channels

28
Q

K+ channel activation enters a slow neg feedback loop, explain this

A

Channel activation leads to a hyperpolarization that decr prob of activating more channels

29
Q

What is action potential threshold?

A

Minimum dep needed to fire an AP. AP WILL NOT fire if Vm is under threshold. AP is an all or non phenomenon

NOTHING will make is fire if its under threshold.

30
Q

How does Non-propagated dep spread?

slide 23

A

Passiviely though local current flow, this is called electronic conduction

we are not hitting threshold at the axon hillock

31
Q

Why does the dep signal decr over distance as it moves down the axon?

A

Ionic charges dissipate within an area and charges leak out (leaky membrane)

32
Q

What is length constant?

A

the distance that 37% of vmax is reached

vmax is the highest amplitude signal

33
Q

What factors influence length consant?

A

Membrane resistance and internal resistance within a cell

internal resistance=interaxonal resistance

34
Q

If you have a high Rm (membeane resistance and low RI what does this mean for the length constant?

A

Larger length constant

35
Q

length constant is ____ to Rm and ____ to Ri

A

directly proportional, inversely prop

36
Q

How is AP maintained along the axon?

A

The peak membrane potential along an axon during an AP remains consistenly dep

37
Q

What is absolute refractory period?

A

A 2nd action potential can NOT fire b/c Na+ channels can not yet be re-activated-either in their open or inactivated state

here, the mem potenital is so dep that its imposible for na+ to be reac to fire ap

38
Q

What is relative refractory period?

A

A much greater dep is required for an ap to fire. Still active voltage gated K+ channels move membrane away from threshold potential.

mostly contributed by the activation of K+ channels openihng, K+ efflux, and hyperpol. This is after hyperpol so dep is needed for ap to take place

39
Q

What is needed in order for a charge in membrane potential?

A

Charges must be re-distributed across the membrane-the membrane must be changed

40
Q

Time needed to charge membrane to change Vm is the ?

A

rate limiting evenft for AP propagation (dictates firing propagation)

41
Q

What is time constant (t)

A

The time it takes for the change in Vm to reach 63% of its final value.

small neurons=small memrane amt= fast charging= quick time constant
opposite for large neurons

42
Q

Myelination ____ conduction velocity because Rm ____ length constant and Cm____ time constant.

A

increases, increases, decreases

Insulating nature of myelin will incr Rm
Cm decr bc or addition of membrane myelin

43
Q

Saltatory conductions: where propagation along myelinated axons where AP jumps from one node to the next. How does myelination affect Rm, Cm, Vm, Conduction velocity, and length constant

A

Incr Rm
Decr Cm (at myelination site)
Decr Vm
Incr conduction velocity
Incr Length constant

length constant is incr bc channels can be distributed farther apart bc signal will be maintained over a greater distance

44
Q

For an unmyelinated axon it has ____ conduction because of ____

A

slower , local current flow (electrotonic conduction)

areas of de-mye = nodes of ranvier, and this is where Na+ ions collect and where depolarization takes place to trigger dep

45
Q

For myelinated axons it has ____ conduction because of ____.

A

Faster, saltatory conduction (action potential jumps from node to node)

46
Q

What is multiple sclerosis?

A

An autoimmune degenerative disease of an axon demyelination. This causes conduction velocity to dec. Channels tend to re-distribute along the axon and action potential propagate through passive current flow whihc is much less effective

47
Q

Conduction velocity is influenced by what two things?

A

Myelination and axonal size

Ri decr in. proportiion to the square of the axon diameter

Neurosciences (28 decks)

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