Membrane potentials and action potentials Flashcards
When is the electrochemical equilibrium met?
Electrochemical equilibrium has been reached when the concentration gradient exactly balances the electrical gradient.
What is the equilibrium potential?
The potential at which electrochemical equilibrium has been reached. It is the potential that prevents diffusion of the ion down its concentration gradient
What is the nernst equation used for?
To calculate equilibrium potential (mV).
Limitations of the nernst equation?
Biological membranes are not 100% uniquely selective for an ion - leakage of some ions through the membrane.
Where can action potentials take place?
Excitable cells (Neurone, muscle cell and some endocrine tissues).
How is the resting potential maintained?
Membrane is more permeable to potassium than sodium. Potassium leaves the cell resulting in a negative value of -70mV.
How is an action potential triggered?
Stimulus depolarises membrane potential. If a threshold is reached, action potential is triggered.
What happens during depolarisation?
Voltage gated sodium ion channels open quickly. Sodium ions move into cell quickly. Voltage gated potassium ion channels open slowly. Potassium ions move out of cell. Overall more sodium ions are moving into cell that potassium ions moving out.
What happens during start of repolarisation?
Voltage gated sodium ion channel inactivation gate closed. Sodium entry stops. More potassium ion channels open. Potassium ions leave the cell.
Why is there an absolute refractory period at the start of repolarisation?
Voltage gated sodium ion channels inactivation gate is closed. New action potential can’t be triggered even with a strong stimulus.
What occurs later in repolarisation?
Voltage gated sodium ion channel activation AND Inactivation gates close.
Why does hyperpolarisation take place?
Voltage gated potassium ion channels take a while to close.
What occurs during hyperpolarisation?
Membrane potential moves closer to the K+ equilibrium, some voltage-gated K+ channels then close.
Membrane potential returns to the resting potential
When is the absolute refractory period?
Start of repolarisation.
When is there a relative refractory period?
After hyperpolarisation.
