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258 midterm > mem and action potentials > Flashcards

mem and action potentials Flashcards

1
Q

what is resting mem potential (Vm)

A

electrical potential difference across the mem

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2
Q

t/f there are no exchange of ions when the meme is at rest

A

false, there are no massive exchanges but there are still a little so the mem can stay at rest

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3
Q

where are Na+ and K+ most prominent at rest

A

there is more Na+ outside the cell at rest and theres more K+ inside at rest

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4
Q

what would happen if the mem was only permeable to K+

A

K+ would diffuse down its concentration gradient until the electrical pot across the mem counters the K+ diffusion

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5
Q

if the mem was only permeable to K+ when would the mvt of K+ stop

A

when the [ ] diff would = electrical difference

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6
Q

what is the electrical pot that counters net diffusion of K+ called

A

K+ equilibrium (Ek) or the Nernst pot for K+

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7
Q

what is called the electrical pot across a mem that exactly opposes the net diffusion of a particular ion thru the mem

A

the Nernst potential or the equilibrium potential

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8
Q

how is the Nernst pot determined

A

by calculating the ratio of the [ ] of that particular ion on the 2 sides of the mem

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9
Q

what is the Nernst equation

A

EMF = ± 61 log ( [inside] / [outside] )

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10
Q

what is the EMF

A

electromotive force that drives ions from inside to outside the cell and vis versa

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11
Q

how is the sign determined in the Nernst equation

A

if the ion is positive than the sign of the equation is negative

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12
Q

what would happen if the mem was only permeable to Na+

A

Na+ would diffuse down its [ ] gradient until a pot across the mem counter the Na+ diffusion which will stop the Na+ mvt

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13
Q

what does the permeability depend on

A

-concentration of respective ions on the inside and outside of the mem
-permeability of the mem to each ion
-polarity of the electrical charge of ions positive or negative

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14
Q

why is Vm so much closer to the Nernst pot of K+ than to it of Na+

A

because the mem is far more permeable to K+

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15
Q

what are the transport methods and their properties of resting n. mem

A

Leak channels; much more permeable to K+ than Na+

and Na+/K+ pump; net increase of 1 positive charge outside (more negativity inside)

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16
Q

what is the resting mem pot for large n. fibers (motor neurons) and for small neurons (interneurons) of nervous sys

A

large n. fibers: -90mV
small neurons of nervous sys: -70mV

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17
Q

what are the 3 factors that the resting mem pot depend on

A

-diffusion of K+ & Na+ ions : K+ (inside to outside) and Na+ (outside to inside)
-permeability of ions thru leak channels: P to K+&raquo_space; P to Na+ (about 100 times more)
-Na+/K+ pump: creates more negativity inside (3 Na+ go outside and 2 K+ go inside)

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18
Q

t/f the resting mem pot is closer to the equilibrium pot for the ion w the lowest permeability

A

w the highest permeability

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19
Q

what are some synonyms of a.p

A

spike, impulse or firing

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20
Q

what is the name for a very rapid change in the mem pot from - to + values and return back to initial resting pot level

A

action potential

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21
Q

t/f if the impulse is higher the amplitude of the ap with be higher as well

A

false, an ap is an all-or-none event, either it occurs fully or it doesn’t occur at all (amplitude of an ap never changes)

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22
Q

what is the path of an ap

A

it moves along the nerve fiber until it comes to the end of the fiber

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23
Q

what are the functions of an ap

A

-transmitting n. signals
-rapid transmission over distance
-encoding info (neuronal language)

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24
Q

from where to where does the ap transfer sensory info

A

transfers from pns to cns

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25
Q

from where to where does the ap transfer motor info

A

transfers from cns to pns

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26
Q

can the ap also transfer info from one part of the cns to another part of the cns

A

yes

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27
Q

speed of transmission (conduction velocity) of ap depends on what

A

fiber size and whether it is myelinated

28
Q

which ap will travel faster btw proprioception, ankle injury and a pressure on the skin

A

proprioception is fastest, pressure on skin and ankle injury is the last to be felt

29
Q

what can vary in an ap depending on the type of pressure applied to the skin

A

the frequency of the ap; a stronger stimulus will cause a higher frequency of ap

30
Q

what is the resting state of the n. action pot

A

-90mV

31
Q

what is the depolarization (how fast is it and what causes it)

A
  • -90 to 35 mV
    -0.1 ms period (very rapid)
    -caused by the sudden opening of the Na+ channels, Na+ ions flow to inside the cell
32
Q

what is repolarization (what closes and what opens, what results after)

A

-Na+ channels begin to close, Na+ ions stop flowing inside
-K+ channels open slowly; K+ ions start to flow inside
this re-establishes the negativity of the resting mem pot

33
Q

what is the afterpotential (what causes it)

A

-less than -90 mV
-caused by K+ channels that remain open for a few milliseconds after repolarization of the mem is completed
-excess K+ flows out of the mem

34
Q

what is the back to resting stage (what causes it)

A

the closing of the K+ channels

35
Q

different stages of the ap are due to the activation of what protein channels on the n. mem

A

voltage-gated Na+ channels
voltage-gated K+ channels

36
Q

the voltage gated channels are sensitive to what and are considered what kind of diffusion

A

changes in mem electrical pot
simple diffusion (electrical gradient is used so no need for E)

37
Q

where are the 2 gates situated on the Na+ channels

A

the activation gate is on the exterior side of the mem
the inactivation gate is on the interior side of the mem

38
Q

what are the states of the gates at resting state

A

activation gate is closed and inactivation gate is open
no entering of Na+ ions

39
Q

what are the states of the gates at activated state (depolarization); what causes it and what flows in or out

A

-activation gate and inactivation gate are both open
-sudden opening of the activation gate is due to shifting of the mem pot towards positive values
-sodium ions flow inside

40
Q

what are the states of the gates at inactivated state (repolarization); when is the gate activated, what stops flowing in/out

A

activation gate is open and inactivation gate is closed
inactivation gate is activated when mem pot increases above 0mV
Na+ ions stop to flow inside and the mem pot recovers back to resting state

41
Q

what is the opening threshold for the Gated sodium channels and what happens to the permeability to Na+

A

-70 to -50 mV
permeability to Na+ increases to 500 to 5000 times more than at rest

42
Q

when can the inactivation gate reopen after repolarization

A

only when the mem returns to resting potential

43
Q

where is the gate situated in a gated K+ channel

A

interior side of mem

44
Q

what are the 2 states of the gate in the K+ channel

A

resting state; gate is closed
slow activation state; gate is open

45
Q

what happens in the slow activation state (repolarization); when are the K+ channels activated, what opens as the other closes, what flows out and what does it accelerates repolarization towards

A

they are activated when the meme pot increases above 0mV
gates open slowly at the same time as the Na+ channels begin to close
K+ ions flow outside
it accelerates repolarization towards resting pot

46
Q

what happens during undershoot ; what channels are open, what excess of ions flow out of the cell

A

K+ channels remian open for a few milliseconds after repolarization of mem is completed
excess K+ ions flow outside of cell

47
Q

what gate closes at back to resting state

A

K+ gate closes & mem pot comes back to -90mV

48
Q

what is the threshold for initiation

A

level of mem pot at which the positive feedback cycle is created (point of no return)

49
Q

when does the threshold occur

A

when the nb of Na+ ions entering the nerve becomes greater than the number of K+ ions leaving the n.

50
Q

what is the threshold for a nerve with a Vm of -90mV

A

about -65mV

51
Q

what causes the initial increase in mem pot that reaches the threshold

A

electrical stimulation (tingling feeling in physio tx)
mechanical stimulation (poked by a needle)
chemical stimulation (neurotransmitters)

52
Q

the amplitude of an AP is ___ of the ___ of the stimulus that evokes it

A

independant
intensity

53
Q

the frequency of firing is ___ on the intensity of the stimulus

A

dependant

54
Q

what is the period during which a new AP cannot occur as long as the mem is still depolarized from the preceding ap

A

absolute refractory period

55
Q

why can’t a new ap be generated during the absolute refractory period

A

bc
-Na+ channels are inactivated
- mem has to return near original resting pot to allow inactivation gates to open (can’t restimulate a neuron thats already there)

56
Q

what is the period that follows the absolute refractory period during which a new ap can occur in response to a stronger stimulus than normal

A

relative refractory period

57
Q

why can an ap only be generated with a stronger stimulus than normal during the relative refractory period

A

bc
-some Na+ channels start to go back to resting state and others are still inactivated (wont have the same nb of Na+ ions to start with)
-K+ channels are still open and the mem is hypolarized (during the undershoot bc K+ ions are still leaving the cell)

58
Q

myelin is an extension of what particular cells

A

glial cells

59
Q

what are glial cells called in the cns and in the pns

A

pns: schwann cells
cns: oligodendrocytes

60
Q

what is myelin sheat

A

fatty white substance that surrounds the axon and thus isolating n. fibers bc ions can’t flow significantly through thick myelin

61
Q

what interrups the myelin sheat every 1 to 3 mm

A

nodes of Ranvier

62
Q

where can the exchange of ions occur (ap generated) on a myelinated axon

A

only at the level of nodes of Ranvier (where the voltage gated channels are located), and ap are conducted from node to node

63
Q

what is saltatory conduction (what does it do concerning E and what is the conduction velocity)

A

it conserves energy for axon (little metabolism required to re-establish ionic [ ] differences)
conduction velocity varies from as little as 0.25 m/s in unmyelinated fibers to as great as 120 m/s in large myelinated fibers

64
Q

how does the propagation of ap work in unmyelinated n. fibers (what makes the adjacent portions of the mem reach the threshold and what is the conduction velocity)

A

ap excites adjacent portions of mem resulting in propagation of the ap
when Na+ ions flow to adjacent area; they increase voltage of adjacent area to the threshold level which initiates adjacent ap
conduction velocity is 0.25m/s

65
Q

what is MS

A

immune-mediated inflammatory disease that causes the demyelination of the cns resulting in m. weakness, loss of sensation and death

66
Q

how does the all or nothing principle apply to MS

A

if conditions arent right; it will stop altogether ap propagation

258 midterm (6 decks)

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