3 - Resting potential Flashcards
What is diffusion?
Spontaneous movement of a substance down it’s concentration gradient. (Membrane must be permeable)
What is flux?
What is it measured in?
The rate of transfer of molecules.
No. of molecules that cross a unit area per unit time.
molecules per metre squared per second.
What is the flux in a dynamic equilibrium?
No net flux.
What are the basic properties of ions?
They are charged.
Opposites attract, like charges repel.
What is voltage?
Potential difference.
Measured in volts.
Generated by ions that produce a charge gradient.
What is current?
The movement of ions due to a potential difference.
Measured in Amps.
What is resistance?
A measure of how hard it is for current to flow through a material.
Measured in ohms.
How is membrane potential measured?
A reference electrode is placed outside the cell (saline solution) at 0 volts (as no resistance).
Another electrode is placed inside the cell which measures the voltage difference between that and the reference.
Inside is more negative.
Resting membrane potential definition?
e.m.f. (voltage) between the inside and outside of a cell.
What features of the lipid membrane make it hard for things to pass across?
High resistance
Low permeability to ions.
Very hydrophobic.
How do ions travel through the lipid membrane?
Ion channels are permeable pores in the membrane.
What makes ion channels open and close?
Depends on the trans-membrane voltage,
ligands or mechanical forces.
What ions have specific ion channels?
K+
Na+
Cl-
Ca2+
If the membrane is impermeable to all ions, what is the membrane potential?
0 V
If the membrane is only permeable to K+, what is the membrane potential?
K+ diffuses and the voltage across the membrane increases (= membrane potential).
Direction of flux is indicated by conc. gradient.
