Membrane Properties Flashcards
What is membrane permeability?
How easily a substance can move through a membrane
What determines ion permeability?
The amount of channels open for that ion
What is membrane conductance?
Describes how easily electric current flows through the cell membrane
Quantified in siemens (S)
What is membrane resistance?
The inverse of conductance, quantified in ohms
What is the driving force and what two forces make it up?
The net electrochemical force acting on an ion
1) The total electrical charge distribution across the cell membrane
2) the ion concentration difference across the cell membrane
What is Ohm’s law?
V=IR
The flow of ions across the membrane depends directly on both the magnitude of the driving force for that ion and the conductance of the membrane to that ion
What is the membrane current?
Direction of electrical current that flows across a membrane.
Describe an inward membrane current.
Makes the interior of the cell more positive (less negative
Describe an outward membrane current.
Makes the interior of the cell less positive (more negative)
What is the relationship between membrane current and membrane potential?
Membrane current starts and ends instantly, with the opening and closing of a channel
Membrane potential changes more slowly than current
Why does membrane potential change more slowly than membrane current?
When current begins flowing, it changes the charge stored on the cell’s capacitance, and this change requires time
Why does membrane potential eventually stop changing?
As charge accumulates inside the cell, the membrane potential shifts in the positive direction, increasing the driving force for efflux of K
Eventually K efflux will match charge influx, and the potential will stop changing
What is the membrane time constant?
A measure of the rate at which a cell’s membrane potential change sin response to steady flow of current
Product of Capacitance (Cm) and membrane resistance (Rm)
What is capacitance directly proportional to?
Total membrane surface area
What is capacitance inversely proportional to?
Membrane thickness
