Membrane potentials

Question 1

Na+/K+ pump How many ions in and out

Answer 1

3 sodium ions OUT
2 Potassium ions IN

Question 2

Which ions are on the inside and outside more abundant

Answer 2

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.

Question 3

Describe the potassium leak

Answer 3

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.

Question 4

Describe the formed electrical gradient

Answer 4

More negative charge inside the cell - Separation of positive and negatively charged ions, establishing a membrane potential.

Question 5

What is a membrane potential

Answer 5

Voltage across the plasma membrane

Question 6

What is a resting potential

Answer 6

Membrane potential of a cell not sending signals (-70mV)

Question 7

What is the Nernst equation

Answer 7

Eion = 62 mV (log[ion]outside / [ion]inside)

Used to calculate the equilibrium potential of a specific ion in a cell.

Question 8

What is the equilibrium potential

Answer 8

The membrane potential at which the electrical and chemical gradients of one specific ion are balanced.

Question 9

What is the goldman equation

Answer 9

Lol.

Used to calculate the resting membrane potential of a cell taking into account multiple ion permabilities

Question 10

What is depolarisation

Answer 10

Membrane potential is more positive than resting potential

Question 11

What is repolarisation

Answer 11

Membrane potential returns to resting potential after depolarisation

Question 12

What is hyperpolarisation

Answer 12

Membrane potential is more negative than the resting potential

Question 13

Why do changes in membrane potential occur

Answer 13

Opening and closing of gated ion channels in response to stimuli

Question 14

How are neuronal and cardiac action potentials different

Answer 14

Cardiac cells have a longer action potential.
Neuronal cells have -70mV rest, cardiac -90mV

Question 15

What happens when a sufficient depolarising stimulus above the threshold is applied to a neuronal cell

Answer 15

Potassium and sodium ion channels open. Lots of positive sodium moves into the cell, making the membrane potential more positive (Depolarisation)

Question 16

Why is the equilibrium potential never reached

Answer 16

The ion gradient would be balanced. However, the sodium ion channels inactivate when the membrane potential reaches 40mV to prevent this. (voltage sensitivity)

Question 17

What happens after inactivation of voltage gated sodium ion channels

Answer 17

Potassium ions leave the cell. As they are positive, the membrane potential begins to decrease (repolarisation) till hyperpolarisation.

Question 18

What cannot occur in hyperpolarisation

Answer 18

Another action potential cannot be stimulated.

Question 19

What do some drugs do to prevent an action potential being stimulated

Answer 19

Block sodium ion chanels

Question 20

What happens when an impulse reaches the end of the axon terminal

Answer 20

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.

Question 21

Describe the generation of a cardiac action potential

Answer 21

0. Depolarisation - Sodium channels open
1. Repolarisation begins. Sodium channels inactivate, potassium channels open.
2. Plateau - Potassium channels still open, some calcium channels then open. Plateau occurs, little net change in potential difference.
3. Repolarisation - Calcium channels close and potassium open, potassium leaves and potential difference decreases.
4. Most sodium and potassium channels are closed

Question 22

What is the necessity of a cardiac action potential

Answer 22

Controls the rhythm and synchronicity of contractions of the heart.