Membrane potentials
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Na+/K+ pump How many ions in and out
3 sodium ions OUT 2 Potassium ions IN
Which ions are on the inside and outside more abundant
More sodium outside (extracellular) More potassium inside (intracellular) Therefore potassium wants to move out of the cell. (conc gradient) while sodium wants to move out.
Describe the potassium leak
Potassium moves out of the cell down its conc gradient. Potassium leaves the cell through K+ channels in the cell membrane, leaving behind the negatively charged anions.
Describe the formed electrical gradient
More negative charge inside the cell - Separation of positive and negatively charged ions, establishing a membrane potential.
What is a membrane potential
Voltage across the plasma membrane
What is a resting potential
Membrane potential of a cell not sending signals (-70mV)
What is the Nernst equation
Eion = 62 mV (log[ion]outside / [ion]inside) Used to calculate the equilibrium potential of a specific ion in a cell.
What is the equilibrium potential
The membrane potential at which the electrical and chemical gradients of one specific ion are balanced.
What is the goldman equation
Lol. Used to calculate the resting membrane potential of a cell taking into account multiple ion permabilities
What is depolarisation
Membrane potential is more positive than resting potential
What is repolarisation
Membrane potential returns to resting potential after depolarisation
What is hyperpolarisation
Membrane potential is more negative than the resting potential
Why do changes in membrane potential occur
Opening and closing of gated ion channels in response to stimuli
How are neuronal and cardiac action potentials different
Cardiac cells have a longer action potential. Neuronal cells have -70mV rest, cardiac -90mV
What happens when a sufficient depolarising stimulus above the threshold is applied to a neuronal cell
Potassium and sodium ion channels open. Lots of positive sodium moves into the cell, making the membrane potential more positive (Depolarisation)
Why is the equilibrium potential never reached
The ion gradient would be balanced. However, the sodium ion channels inactivate when the membrane potential reaches 40mV to prevent this. (voltage sensitivity)
What happens after inactivation of voltage gated sodium ion channels
Potassium ions leave the cell. As they are positive, the membrane potential begins to decrease (repolarisation) till hyperpolarisation.
What cannot occur in hyperpolarisation
Another action potential cannot be stimulated.
What do some drugs do to prevent an action potential being stimulated
Block sodium ion chanels
What happens when an impulse reaches the end of the axon terminal
Reaches the synapse, where an action potential will cause neurotransmitter release. Calcium comes into cell to allow neurotransmitter vesicle to fuse with membrane to release neurotransmitter, affecting the postsynaptic membrane.
Describe the generation of a cardiac action potential
• Depolarisation - Sodium channels open • Repolarisation begins. Sodium channels inactivate, potassium channels open. • Plateau - Potassium channels still open, some calcium channels then open. Plateau occurs, little net change in potential difference. • Repolarisation - Calcium channels close and potassium open, potassium leaves and potential difference decreases. • Most sodium and potassium channels are closed
What is the necessity of a cardiac action potential
Controls the rhythm and synchronicity of contractions of the heart.