Changes%20in%20electrical%20gradients

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Changes in electrical gradients

• Electrical disequilibrium
• Consequences of electrical disequilibrium
• Resting membrane potential
• Equilibrium potential
• Membrane depolarization and hyperpolarization

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Cell in the body are

• In chemical disequilibrium
• In osmotic equilibrium
• In electrical disequilibrium few extra negative
  ions inside cells and their matching positive
  ions are outside

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Na Cl- Organic Anions K
Na Cl- Organic anions K
Distribution of main ions
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3 Na
Na Cl- Organic Anions K
Na Cl- Organic anions K
ATPase
2 K
Anionic proteins are trapped Inside the cell
Electrical disequilibrium across the cell
membrane ? membrane potential difference
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How does electrical charge separation occur?
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The cell membrane Is an insulator
There are more positive charges outside and more
negative charges inside
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Na Cl- Organic Anions K
Na Cl- Organic anions K
Electrochemical gradient is a combination of the
electrical and chemical gradients
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Electrochemical gradient

• Electrical gradients and chemical gradients
  across the cell membrane
• Electrical force moves K into the cell (cell has
  more neg. charges)
• Chemical gradient favors K to leave the cell (K
  concentration is low outside)
• These forces reach a steady state

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Membrane Resting Potential

• The voltage difference across the cell membrane
  when there is an electrochemical gradient at a
  steady state
• There is a voltage difference between the inside
  and the outside (potential difference)

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The value for the resting membrane potential
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Membrane Potential

• Vm is the membrane potential (millivolts)
• Resting membrane potential for nerves and muscles
  is -40 mV to -90 mV
• The resting membrane potential is determined by
  K

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K channels are open during the resting membrane
potential.
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If K channels are open.
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Equilibrium Potential

• The membrane potential when the channels for a
  particular ion are open is called the equilibrium
  potential for that particular ion.
• At EK the rate of ions moving in due to the
  electrical gradient equals the rate of ions
  leaving because of the concentration gradient.
• EK is close to the resting membrane potential

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Factors that are important for the equilibrium
potential for an ion

• Only channels for that ion are open
• The charge of the ion
• Concentration of the ion inside the cell
• Concentration of the ion outside the cell

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At the equilibrium potential for Na
Artificial cell, Na is leaving because the
inside became after the inward Movement of Na
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Currents during resting membrane potential
K outward current is much stronger than Na
inward current. Lots of K channels are open,
few Na channels are open at rest.