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HUMAN PHYS > Electric Potential of Cells > Flashcards

Electric Potential of Cells Flashcards

1
Q

Potential (Potential difference)

A

The voltage difference between two points due to separated electrical charges of opposite sign; these separated charges have the potential to do work

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2
Q

Membrane potential

A

The voltage difference between the inside and outside of a cell

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3
Q

Equilibrium potential

A

The voltage difference across a membrane that produces a flux of a given ion species that is equal but opposite to the flux due to the concentration gradient of that same ion
- where the net flow through any
open channel is 0
- indicates that the chemical and electrical
forces for that ion are in balance

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4
Q

Resting membrane potential (Vm)

A

The steady potential of an unstimulated cell
- RMP of ALL cells is NEGATIVE; -50 to -90mV in excitable cells and -5 to -15mV for non-excitable cells

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5
Q

Graded potential

A

A potential change of variable amplitude and duration that is conducted decrementally (further away from stimulus); has no threshold or refractory period
Can be:
- depolarizing OR hyperpolarizing
- vary in size d/t stimulus strength
- decay with distance from site of initial stimulus

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6
Q

Action potential

A

A brief all-or-none depolarization of the membrane, which reverses polarity in neurons; has a threshold and refractory period and is conducted without decrement

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7
Q

Synaptic potential

A

A graded potential change produced in the postsynaptic neuron in response to the release of a neurotransmitter by a presynaptic terminal; may be depolarizing (an excitatory postsynaptic potential or EPSP) or hyperpolarizing (an inhibitory postsynaptic potential or
IPSP)

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8
Q

Receptor potential

A

A graded potential produced at the peripheral endings of afferent neurons (or in separate receptor cells) in response to a stimulus

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9
Q

Pacemaker potential

A

A spontaneously occurring graded potential change that occurs in certain specialized cells

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10
Q

Threshold potential

A

The membrane potential at which an action potential is initiated

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11
Q

Energy

A

the ability of an object to do work on another object

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12
Q

Kinetic Energy

A

energy in motion

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13
Q

Potential energy

A

energy at rest

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14
Q

Effects of quantity and distance on separated charges

A

Force:
- INCREASES when charges are closer together
- INCREASES when there are MORE charges being separated

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15
Q

Ohm’s Law

A

V=IR
I=V/R
R = Resistance due to presence of the plasma membrane (measured in Ohms)
V = Difference in electric potential energy on either side of the membrane (measured in volts)
I = Flow of charged particles through “conductors” in the membrane (measured in Amperes

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16
Q

Capacitor

A

a device that can store energy by accumulating electric charges on two closely spaced surfaces that are insulated from one another

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17
Q

Insulator

A

structure that separates opposing surfaces so that the contents of one surface do not bleed into the other surface

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18
Q

Conductance (G)

A

a measure of how easily an ion moves through a membrane; reciprocal of resistance
- HIGH conductance= LOW resistance
- ion channels are conductors when open

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19
Q

Resistance (R)

A

a measure of how DIFFICULT an ion moves through a membrane; reciprocal of conductance
- HIGH resistance= LOW conductance
- ion channels are mini-resistors when closed

20
Q

Determinant of resting membrane potential

A
  • differences in [ion] in the ICF and ECF
  • difference in membrane permeabilities to the ion
21
Q

Nernst equation

A

describes the equilibrium potential of an ion
equation: 61/Z x log ([out]/[in])

22
Q

E (Na+)

A

+60 mV

23
Q

E (K+)

A

-90 mV

24
Q

Net driving force

A

must consider both concentration and
electrical potential differences so can be calculated:
Vm-Eion
ex: E(Na+)= +60mV –> -70mV-60mV= -130mV which means driving force favors Na+ ENTERING the cell

25
Q

Ionic current

A

refers to ion movement when AND membrane has conductance to that ion; can be calculated:
Ix = gx(Vm –Ex)

26
Q

Goldman-Hodgkin-Katz Equation

A

determines RMP due to the influences of the 3 major ions on RMP
Vm= 61 log (Pk[Kout]+PNa[Naout]+PCl[Clin]/PK[Kin]+PNa[Nain]+PCl[Clout])
= -70mV

27
Q

Permeability coefficient of K

A

1 (most permeable to membrane)

28
Q

Permeability coefficient of Na

A

0.04

29
Q

Permeability coefficient of Cl

A

0.45

30
Q

Contribution of K to RMP

A

membrane is MOST permeable to K+, with the most leak channels which is why RMP is close to E(K)

31
Q

Contribution of Na/K ATPase pump to RMP

A

3Na out and 2K which generates a small electric potential, making RMP negative

32
Q

Contribution of Cl to RMP

A

leak channels for Cl- exist, but there is no pump to move the ions so not a big contribution

33
Q

Contribution of Na to RMP

A

membrane is not as permeable to Na+, with fewer leak channels which is why RMP is close to E(K) and NOT E(Na)

34
Q

Depolarization

A

potential moving from RMP to less
negative (closer to zero) values

35
Q

Overshoot

A

a reversal of
membrane polarity, when the
inside of the cell becomes more
positive than the outside.

36
Q

What ion channel is/are responsible for the OVERSHOOT?

A

Na+ activation gates slow to close and K+ channel slow to open

37
Q

Repolarization

A

potential returning to the RMP
from a depolarized state

38
Q

Hyperpolarization (Undershoot)

A

potential becoming more negative
than the RMP

39
Q

What ion channel is/are responsible for the UNDERSHOOT?

A

K+ leak channels

40
Q

Summation

A

addition of graded potentials from several stimuli that occur in rapid succession before each graded potential has died out
- allows the graded potentials to be added up to generate enough current to bring cell past threshold and fire an action potential

41
Q

Time constant (τ)

A

the time that it takes for the voltage to reach 63% of its final value following injection of a current OR the time it takes voltage to drop to 37% of its initial value; depending on membrane resistance and membrane capacitance; is what allows for temporal summation
equation: τ= RmCm

42
Q

Main contributor to the time constant

A

membrane resistance
= if the membrane has high resistance OR if channel is CLOSED

43
Q

Temporal summation

A

the processing of multiple subthreshold potentials over a set period of time

44
Q

Length constant (λ)

A

thee distance from the site of current
injection where the potential has fallen by 63% of the original value; indicates how far a depolarizing current will spread along a
nerve; the longer the length constant the further the current spreads down the neuron
- important determinant of
synaptic efficacy
λ= (rm/r/i)^1/2

45
Q

When is the length constant the greatest?

A
  • LOW internal resistance
  • HIGH membrane resistance
  • LARGE diameter of a neuron (makes for LOW internal resistance)
46
Q
A

HUMAN PHYS (7 decks)

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