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Vet Physiology > Equilibrium, Resting Membrane, and Action Potentials > Flashcards

Equilibrium, Resting Membrane, and Action Potentials Flashcards

1
Q

what is RMP?

A

the potential difference that exists across membranes in the period between action potentials

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2
Q

how are RMPs established?

A

by diffusion potentials

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3
Q

what are diffusion potentials?

A
  • defined as the potential difference generated across a membrane WHEN A CHARGED ION DIFFUSES DOWN CONC. GRADIENT (K+ increases inside)
  • can be positive or negative, depending on charge of ion
  • set by K+ leak and channels and maintained by Na+/K+ ATPase pump
    • K+ leaks out of cell and carries + charge -> inside of cell is (-) -> cation Na wants to rush into cell
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4
Q

what ions contribute most to RMP?

A
  • ions with high permeabilities
  • K+, Cl-
  • K+ separated from immobile anions inside cell
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5
Q

normal RMP range?

A

usually -70 to -90 mV

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6
Q

Na+/K+ ATPase

A
  • helps to maintain K+ concentration gradient across the membrane
  • helps to set K+ diffusion potential
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7
Q

why is RMP always close to K equilibrium potential?

A

RMP is negative because there are more Na ions outside cell than K ions inside cell (membrane more permeable to K+ than Na+)

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8
Q

K equilibrium potential=

A

-85 to -90 mV

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9
Q

K+ is in equilibrium when…

A

cell is 85-90 mV lower than EC environment

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10
Q

K+ equilibrium potential is point at which…

A

movement of K+ INTO cell because of negative electrical potential is balanced by diffusion of K+ OUT of cell due to concentration gradient

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11
Q

at K+ equilibrium…

A

electrical and diffusion forces are equal and opposite

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12
Q

driving force=

A

difference between the measured membrane potential and the ion’s calculated equilibrium potential

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13
Q

when driving force is negative…

A
  • ion will enter cell if it is a cation and leave cell if it is an anion
  • membrane potential is too negative- try to bring it towards equilibrium potential
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14
Q

Action Potentials (AP)

A
  • transmit information in nervous systems and all muscles
  • occurs in EXCITABLE cells- rapid depolarization followed by depolarization
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15
Q

depolarization=

A

membrane potential LESS negative

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16
Q

hyperpolarization=

A

membrane potential MORE negative; harder to get new AP when in this state

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17
Q

inward current=

A

Na+, flow of positive charge into cell (must occur for AP)

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18
Q

outward current=

A

K+, flow of positive charge out of cell; helps reset Na+K+ pump working

19
Q

threshold potential

A

membrane potential at which AP is inevitable

20
Q

overshoot

A

portion of AP where membrane potential is positive

21
Q

undershoot

A

portion of AP where membrane potential is more negative than RMP

22
Q

refractory period

A

period during which another AP can’t be generated

23
Q

1st event of AP

A
  • RMP is -70 mV, K+ conductance is high, Na+ conductance low
  • K channels fully open -> K leaks out -> diffusion potential
24
Q

2nd event of AP

A
  • upstroke of AP- membrane depolarization to threshold (-60 mV)
  • voltage-gated Na+ channel
  • rapid opening of activation gates in Na channel, Na flows into cell -> depolarization
25
Q

3rd event of AP

A
  • REPOLARIZATION: inactivation (terminate upstroke) gates on Na+ channels close and K+ channels open (allowing depolarization of membrane)
26
Q

4th event of AP

A

UNDERSHOOT (hyperpolarization): K+ conductance higher than at rest- slowly return to RMP

27
Q

Refractory periods=

A

excitable cells unable to produce normal APs

28
Q

absolute refractory period (ARP)

A
  • majority of APs
  • overlaps with most of the AP
  • no stimulus can occur to cause another AP
  • inactivation gates on Na channels remain closed (once closed) until cell repolarized
29
Q

relative refractory period (RRP)

A
  • from end of ARP until through most of hyperpolarization
  • AP occurs with greater than normal depolarization
  • membrane more negative, it takes more stimulus to reach threshold
30
Q

refractory period timeline

A
  • A: at RMP- activation gate closed, inactivation gate open
  • B: activated by signal- voltage gated and ligand gated
  • C: inactivated state- time and return to RMP required to reset; refractory to subsequent stimulus (inactivation gate closes)
31
Q

characteristics of AP?

A
  • size and shape for a given cell type
  • propagation: APs propogate -> depolarization spreads to adjacent areas on membrane
  • all-or-none response: depolarization either brings to threshold or doesn’t
32
Q

steps in propagation of APs

A
  • APs start close to the cell body of a neurons, spread down the axon via local currents
    1. initial area of axon depolarization to threshold, AP fires, cell interior positive
    2. positive charges inside cell flow towards negative charges in adjacent areas of cell- those areas then depolarized to threshold
    3. at this point, the initial area has repolarized
33
Q

what is conduction velocity of APs?

A

speed at which an AP travels along a nerve or muscle fiber

34
Q

what is a time constant?

A
  • how quickly a membrane depolarized in response to inward Na+ current
  • membrane resistance and capacitance affect the time constant
35
Q

what is resistance?

A
  • high membrane resistance -> current doesn’t readily flow across membrane -> force current to spread internally -> path of least resistance
  • INCREASE time constant
36
Q

what is capacitance?

A

-ability of a membrane to store charge
- high capacitance -> time constant INCREASE- current must discharge membrane before depolarization can occur

37
Q

what is length constant?

A
  • how far depolarization current will spread along a nerve
  • membrane resistance and internal resistance affect length constant
38
Q

longer length constant means…

A

current spreads farther

39
Q

internal resistance is inversely related to…

A
  • how easily current spreads within cytoplasm
  • high resistance, current won’t spread as far
40
Q

current travels farthest when diameter…

A

large, membrane resistance high (force current to flow along interior), internal resistance is lowing o

41
Q

in order to increase conduction velocity, we need to…

A
  1. increase size of the nerve fiber- by increasing diameter of a fiber, internal resistance DECREASES
    - however, there are anatomical limits to nerve size
  2. myeline the nerve fiber-insulation of nerves with lipid will increase membrane resistance and decrease capacitance
    - where nerve insulated and membrane resistance increases, force current to move along interior
    - also increases constant time -> at breaks in myelin sheath, membrane depolarize faster
42
Q

nodes of Ranvier?

A

breaks in myelin sheath every 1-2 mm
- membrane resistance low, current flow and AP occurs

43
Q

Saltatory conduction

A

APs jump from node to node

Vet Physiology (5 decks)

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