ch 12.4 - Flashcards
resting membrane potential
membrane potential of an unstimulated resting cell
3 important concepts regarding the membrane potential:
- The extracellular fluid (ECF) and intracellular fluid (cytosol) differ greatly in ionic composition.
-ecf has high concentrations of sodium and chloride ions , whereas the cytosol has high concentrations of potassium ions + negatively charged proteins. - cells have selectively permeable membranes
- membrane permeability varies by ion
current
movement of charges to eliminate a potential difference
resistance
measure of how much the membrane restricts ion movement
electrochemical gradient
the sum of the chemical and electrical forces acting on that ion across the plasma membrane
chemical gradient
passive movement of ions across the plasma membrane driven by their concentration gradient
electrical gradient
passive movement of ions due to charge differences
equilibrium potential
membrane potential which there is no net movement of a particular ion across the cell membrane
sodium potassium exchange pump
powered by atp
moves 3 sodium (Na) ions out of the cell + 2 potassium (K) ions into the cell per atp
gated ion channels
open and close in response to stimuli
chemically gated ion channels
open when they bind specific chemicals or ligands
voltage gated ion channels
open or close in response to changes in the membrane potential
mechanically gated ion channels
open or close in response to physical distortion of membrane
graded potentials
temporary localized change in the resting membrane potential
- can cause depolarizatio and hyperpolarization
repolarization
returning to normal resting membrane potential after depolarization
action potentials
large depolarization that once initiated, affects the entire excitable membrane
threshold
membrane potential at which an action potential begins
all or none principle
an action potential is either triggered or not
steps of action potentials
- depolarization to threshold
- rapid depolarization
- repolarization
- hyperpolarization
refractory period
a period during which the membrane will not respond normally to additional depolarizing stimuli
propagation
series of steps that move the action potential along the axon
continuous propagation
occurs in unmyelinated axon