3.5: Graded Potentials Flashcards
What is a graded potential
Local changes in membrane potential that vary in degrees of magnitude. For example if membrane potential changes from -70 mV to -50 mV, the graded potential is 20 mV.
Are graded potential’s depolarizing or hyperpolarizing
They can be either, depending on the current flow and resulting change in membrane potential
Graded potentials can sum to generate larger or smaller changes in membrane potential, what is temporal summation
When the same stimulus applies repeatedly over short periods of time
What is spatial summation in relation to graded potentials
Different stimuli generate currents that overlap at a common point on the plasma membrane
What do triggering events do in the membrane and what are they most common channels effected in a cell
They cause gated eye on channels to open, usually chemically or mechanically gated. Most commonly sodium ions
What dictates the magnitude and length of a specific graded potential
The magnitude and length of the triggering event will affect how many channels open
Describe what happens when sodium channels open
Sodium permeability increases as it moves down the concentration and electrical gradient, so membrane potential moves towards the sodium equilibrium potential. This result in depolarization (graded potential) and is confined to a small specialized region of the total plasma membrane (active area)
How do graded potentials cause electrical current flow
Due to the difference in charges caused by the graded potential both inside and outside the membrane, passive flow begins in the active area and the positive charges flow away from the more positive area inside the cell while outside the cell positive charges flow towards the active area. Flow along membrane, not through it, spreading the depolarization in both directions away from the initial site
What hinders electrical current, and how does this relate to lipids
Resistance hinders electrical current, intracellular fluid and extra cellular fluid are good conductors but lipids are not, so currents can only cross membranes through channels
The magnitude of a graded potential is decremental, what does this mean
It means that as the current travels down the membrane it decreases due to some ions leaking through open channels, causing the magnitude of the graded potential to decrease until there is no longer a change in potential. This occurs within millimetres from initial active site
