Maintenance of resting membrane potential

EXAM 4

Chemical gradient + electrical gradient =

electrochemical gradient

Differentially Permeable Membrane

• If allowed, ions move down to electrical chemical gradient

• slightly permeable to Na+ so some Na+ leaks in - leak channels- always open

• more permeable to anionic protein

• membrane very permeable to Cl- (near equilibrium)

Na+/K+ pump (active transport)

• actively maintain RMP

• Moves 3 Na+ out and 2 K+ in - against electrical gradient

• requires ATP

Equilibrium Potential

Transmembrane potential at which no net movement of a particular ion across the cell membrane

Key Concepts

Transmembrane potential exists across cell membranes because

ICF and ECF have different chemical/ion balances cell membrane selectively permeable

(Threshold 100mV)

Graded (local) potential

• Magnitude proportional to stimulus intensity

1. Na- channel open

2. Na+ rushes in

3. membrane potential becomes less negative

4. Doesn’t reach threshold before channels close

   • Produce local changes only

   • Travel short distance

     • decremental decrease in size as spread

     • Increase stimulus intensity increased initial voltage charge, increased distance traveled

What does graded potential produce

local changes only, travel short distance

• decremental - decrease in size as spread

Depolarization

Reduction in membrane potential

• usually due to Na+ channels opening

• As cell becomes less negative, less polarized

Hyperpolarized

increase in membrane

• due to K+ channels opening

• as cell becomes move negative, more polarized

Key concepts grid potential

• Transmembrane potential changes

  • due to altered membrane permeability

  • in response to stimuli