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Human Physiology 1 > Lecture 7 Outline > Flashcards

Lecture 7 Outline Flashcards

1
Q

Electrochemical gradients are dependent on both…

A

concentration & charge

- under physiological conditions, electrochemical gradients are established for K+, Na+ & Cl-

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2
Q

Membrane potential vs RMP

A 
MP of a cell:
due to electrical gradient across a cell membrane
- unequal distribution of charges (ions)
- established by ATPase transporters
measured in mV (millivolts)
not constant: 
- MP can change due to movement of ions

RMP

  • special case of MP, where there is steady-state balance b/t active transport & leakage of ions
  • for most cells, RMP b/t -20mV & -90mV
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3
Q

Define Depolarization

A

more +

- towards 0

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4
Q

Define Hyperpolarization

A

even more -

- even more away from 0

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5
Q

Define repolarization

A

more -

- away from 0

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6
Q

Equilibrium potential definition

A

the membrane potential that exactly opposes the steady state electrochemical gradient for an ion

follows the convention: “inside with respect to outside”

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7
Q

Nernst equation

A

Eion=61/z x log ([ion]out/[ion]in)

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8
Q

Example normal physiological conditions for equilibrium potential

A

K+ -90mV
Na+ +60mV
Ca2+ +122mV
Cl- -81mV

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9
Q

Independence

A

The equilibrium potential for each ion is independent of the concentration of the other ions
- ex: the equilibrium potential for K+ has NO EFFECT on the equilibrium potential for Na+ or Cl-

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10
Q

RMP Goldman Equation

A

RMP (in mV) = 61 log (Pk [K+]out + PNa [Na+]out + PCl [Cl-]in/ Pk [K+]in + PNa [Na+]in + PCl[Cl-]out)

predicts RMP considering 2 factors:

  1. relative permeability of Na+, K+, & Cl-
  2. the concentrations inside & outside the cell
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11
Q

Example normal physiological conditions of RMP

A

Normal, healthy is -78mV RMP

*the ion that has the greatest permeability contributes the most towards determining what the RMP will be

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12
Q

Example kidney failure Equilibrium potential

A

elevated [K+out]

hyperkalemic (10 mM K+)

= -67mV (depolarization)

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13
Q

High Na+ permeability

A

PNa=10 000

RMP = +58mV (VERY positive)

What would cause this?
the opening of VG Na+ channels for ex

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14
Q

Movement of ions changes MP: K+

A

relative concentration inside: high

EP = -90mV

direction of movement when ion channels out: OUT

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15
Q

Movement of ions changes MP: Na+

A

relative concentration inside: low

EP = +60mV

direction of movement when ion channels out: IN

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16
Q

Movement of ions changes MP: Ca2+

A

relative concentration inside: low

EP = +122mV

direction of movement when ion channels out: IN

17
Q

Movement of ions changes MP: Cl-

A

relative concentration inside: low

EP = -81mV

direction of movement when ion channels out: IN

18
Q

Why is the cell membrane an effective insulator?

A

it is able to keep charges separated from each other

19
Q

Define electrochemical gradient

A

combo of an electrical gradient & chemical gradient

- ions subjected to an electrochemical gradient will move

20
Q

Define electrical gradient

A

ex: inside the cell there is more (-) & outside more (+)

21
Q

Define chemical gradient

A

ex: more of the green (-)’s inside than outside

- vice versa with the red (+)’s

22
Q

Describe how to measure MP

A

convention is “inside with respect to outside”

Ex: if a cell has a RMP of -70 mV it is -70mv “inside with respect to outside”

  • take a sharp electrode & poke it inside the neurons & measure the MP “inside with respect to outside”
23
Q

Describe the hypothetical cell with a K+ pump (Active transport) and leakage channels

A

concentration of K+ maintained over time

system is at STEADY STATE where the rate of leakage thru leakage channels is exactly balanced by active transport

NOT equilibrium b/c it requires constant energy

24
Q

Now imagine that the K+ pump (active transport) in the hypothetical cell is stopped (add a poison for ex)

A

K+ would eventually leak out until inside & outside are at an equilibrium

25
Q

How can we make K+ stay inside if we’ve shut off the pump in the hypothetical cell?

A
  • make inside (-)ly charged to attract K+ ions (ADD (-) charges)
  • we say: “Make the inside (-) with respect to the outside”
  • the amount of voltage necessary to keep the K+ inside is called the equilibrium potential, or reversal potential
26
Q

What are the equilibrium potentials of key ions at physiological concentrations?

A

K+ -90mV

Na+ +60mV

Ca2+ +122mV

Cl- -81mV

27
Q

If only one ion was permeant, RMP would be…

A

the equilibrium potential for that ion

ex: if K+ was the only permeant ion, RMP would be -90 mV

however all real cells are permeable to Cl, K+ & Na+ (they’re leaky b/c they have leakage channels…)

so we need an equation to account for leaky ions & their electrochemical gradient

28
Q

What is the relative permeability for Na+, K+, Cl- and anions- (proteins, etc)

A

Na+ 1

K+ 50

Cl- 10

Anions 0

29
Q

Why isn’t Ca2+ in the Goldman Equation (even though there is a difference inside & out for Ca2+)?

A

b/c in a resting cell, Ca2+ is virtually impermeable (NO leakage channels for calcium) so that is why Ca2+ would drop out of this equation

if Ca2+ DIDN’T drop out of this equation it would be about 2 pages to write the whole thing out b/c Ca2+ has a valence of 2

so Ca2+ drops out to:

  1. simplify the math
  2. the resting permeability is 0
30
Q

Why is Cl- flipped for the Goldman Equation?

A

b/c Cl- is a (-)ly charged ion

31
Q

What does it mean that K+ has the HIGHEST permeability (50 compared to 1 for Na+ & 10 for Cl-)?

A

that means that K+ has the MOST INFLUENCE on where the RMP is gonna go

  • therefore, the RMP will tend TOWARDS the equilibrium potential for K+
  • so changes on K+ ion concentrations will have the biggest effects on RMP
32
Q

What happens if only 1 ion is permeant in the Goldman equation?

A

the RMP will be the equilibrium potential for that ion

Ex: if PNa & PCl- (permeability) went to 0, then they will all become 0 & the RMP will be K+ equilibrium

*so the ion that has the greatest permeability contributes the most towards determining what the RMP will be

33
Q

Movement of ions at physiological concentrations depends on what 2 factors?

A
  1. Equilibrium potential &

2. MP of the cell

34
Q

When ion channels open:

A

the ion always moves to make MP = Equilibrium potential

35
Q

Describe what will happen in this physiological condition:

RMP = -78mV Ena = +60mV

A

to make RMP more (+)/closer to +60mV you have to bring more (+)ly charged ions INTO the cell

36
Q

Describe what will happen in this physiological condition: (ADULT NEURONS Cl- low inside cell)
RMP = -78mV Ecl- = -80mV

A

Cl- ions will move IN to make the MP more like the EP

37
Q

Describe what will happen in this physiological condition: Cl- transporter protein (KCC2) not present (EARLY brain development, & epilepsy)
RMP = -78mV Ecl- = -50mV

A
  • EVEN THOUGH there is more (-) outside than inside, Cl- will move OUTside to make the RMP more like the EP
  • therefore, doesn’t really follow the concentration gradient
  • ions don’t always move according to the simple concentration gradient, but they move according to their electrochemical gradient & you can figure out which way they will move when you consider that “the ion always moves to make MP = EP

Human Physiology 1 (32 decks)

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