04 membrane potentials

potential difference refers to a separation of electrical charge

membrane potential is the potential difference that exists across the cell membrane

the greater the amount of charge separation, the gerater the amount of volts

potassium ions are always trying to leave the cell

efflux is flowing outward

potassium wants to go down its concentration gradient

a salty banana - there is potassium in the interior of a cell, sodium on the outside

sodium-potassium pump - 3 sodium ions going out, 2 potassium ions going in

when potassium leaves the cell, the potential difference is greater

sodium is always trying to enter the cell

influx is flowing inward

remember the ions are always trying to go from high concentration to low concentration

the inside of a cell is negative

sodium is positively charged

when sodium enters the cell, the potential difference is lessened

inside of a neuron at rest it is about -70mV

the concentration gradient and the charge gradient are two forces that act upon the RMP

RMP is the resting membrane potential

causes of the RMP - uneven distribution of ions, differentially permeable membrane, sodium-potassium pump

the extracellular fluid is rich in Na+ and Cl-

the cytosol is rich in K+ and protein

the membrane is much less permeable to sodium ions than potassium ions

sodium leaks into the cell much more slowly than potassium leaks out of the cell

more positive charge leaks out than positive charge leaking into the cell

types of membrane potential changes - graded potentials, action potentials

types of ion channels - voltage-gated ion channels, ligand-gated ion channels

when binding of a ligand leads to the opening of Na+ channels then the cell is depolarized as positive ions rush in

ligand-gated Na+ channels make the potential difference less

when the binding of a ligand leads to the opening of K+ channels then the cell is hyperpolarized as the positive ions rush out

ligand-gated K+ channels make the potential difference greater

graded potential location - cell body, dendrite

graded potential distance - short

graded potential amplitude - variable

graded potential stimulus - chemicals, light, pressure, temp

is graded potential positive feedback? no

effect on RMP - small changed

action potential location - axon hillock, axon

action potential distance - long

action potential amplitude - always the same

action potential stimulus - membrane depolarization

is action potential positive feedback? yes

action potential effect on RMP - big changes