Membrane and Action Potentials Flashcards
What is the potassium concentration like in the cells?
[K+] levels are high INSIDE compared to the outside.
What is the sodium concentration like in the cells?
[Na+] levels are high OUTSIDE compared to inside.
What is ATP broken down into?
It is broken down into ADP and inorganic molecules.
What is extrinsic breakdown?
It is an active transport mechanism so requires energy. -
In a concentration gradient, what will the [K+] try to do?
It will try to move out and therefore, decrease the concentration gradient.
Explain the potassium leak.
Potassium moves out the cell (DOWN CONC GRADIENT)
Leaves via potassium channels and so leaves behind the negatively charged molecules.
An imbalance of charges is created due to there being such a very selective membrane.
Explain the electrical gradient.
A potential difference is created because there is a separation of positive and negative charged ions.
MORE NEGATIVE IS INSIDE THE CELL
Explain what is a membrane potential.
Voltage (difference in electrical charge) across the plasma membrane.
Explain what is a resting potential.
The membrane potential of a cell not sending signals.
What produces a concentration gradient?
Sodium - Potassium Pump
What produces an electrical gradient?
Potassium Leak
What influences a membrane potential to be generated?
An electrical gradient across the membrane results in a membrane potential.
Explain what an equilibrium potential is.
The membrane potential at which the electrical and chemical gradients of a specific ion are balanced.
Which equation is used to calculate the equilibrium potential of a specific ion in a cell?
The Nernst equation used to calculate the potential of a specific ion.
Which equation is used to calculate the resting membrane potential of a cell taking into account multiple ion permeabilities?
The Goldman equation is used.
What are the different activities of an ion channel?
Depolarisation // Repolarisation // Hyperpolarisation.
What are the differences in potentials in depolarisation?
Membrane potential is MORE POSITIVE than resting potential.
What are the differences in potentials in repolarisation?
Membrane potential RETURNS to resting potential after depolarisation.
What are the differences in potentials in hyper polarisation?
Membrane potential is MORE NEGATIVE than the resting potential.
Why do changes in the membrane potential occur?
Cells contain gated ion channels which open / close in response to stimuli.
What causes an action potential?
When a depolarisation shifts the membrane potential sufficiently.
Why does the membrane potential not reach E(na)?
This is because the channels inactivate here the membrane potential does not reach E(na).
How do you raise the voltage above the threshold?
The stimulus needs to cause sufficient depolarisation in order to raise the voltage.
Why does depolarisation occur?
It occurs because there is an influx of sodium ions into the cell.
Why does depolarisation occur?
It occurs because there is an influx of potassium ions leaving the cell.
How do nerves send electrical signals?
The action potential is spread along the axon from the soma to the axon to the axon terminal.
The depolarisation spreads from the soma to axon to axon terminal.
The stages which follow the depolarisation stages are: Repolarizing and Resting.
What causes a neurotransmitter release?
An action potential at the synapse causes the neurotransmitter to be released.
What is the difference in cardiac and neuronal action potentials?
With cardiac action potentials, there is no threshold level.
Depolarisation is very fast and this is due to LESS SODIUM activity in the heart.
What is the time difference in action potentials between action potentials
Cardiac is 300 milliseconds whereas neuronal is 5 milliseconds.
So neuronal is quicker than cardiac.
What is stage zero of the cardiac action potential?
Depolarisation occurs.
Sodium channels open.
What is stage one of the cardiac action potential?
Depolarisation occurs.
Sodium channels become inactive.
Potassium channels open.
What is stage two of the cardiac action potential?
Plateau.
Potassium channels are open but some calcium channels are activated too.
Results in plateau stage.
What is stage three of the cardiac action potential?
Repolarisation occurs.
Calcium channels close.
Potassium channels open.
What is stage four of the cardiac action potential?
Most sodium and potassium channels are closed.
What is the purpose of a cardiac action potential?
They underlie the electrical conduction system in the heart.
Controls the rhythm and synchronicity of contractions of the heart.
What mediates membrane depolarisation?
Potassium LEAVES the cell.
