Membrane potentials

Question 1

Where is sodium highest?

Answer 1

Outside the cell

Question 2

Where is potassium highest?

Answer 2

Inside the cell

Question 3

What does the equilibrium potential depend on?

Answer 3

Concentration gradient and electrical potential difference

Question 4

What is an eqn used to estimate equilibrium potential for a given ion?

Answer 4

Nernst eqn

Question 5

Approx. concentration of sodium outside the cell?

Answer 5

140mM

Question 6

Approx. concentration of sodium inside the cell?

Answer 6

14mM

Question 7

Approx. concentration of potassium inside the cell?

Answer 7

120mM

Question 8

Approx. concentration of potassium outside the cell?

Answer 8

4mM

Question 9

Typical equilibrium potential for sodium

Answer 9

+65mV

Question 10

Typical equilibrium potential for potassium

Answer 10

-95mV

Question 11

For uncharged substances, what is considered for equilibrium potential?

Answer 11

ONLY concentration gradient

Question 12

How would you calculate the net driving force?

Answer 12

Membrane potential - Equilibrium potential

Question 13

If the driving force is negative what happens?

Answer 13

Cations will enter the cell and anions will leave

Question 14

If the driving force is positive what happens?

Answer 14

Anions will enter the cell and cations will leave

Question 15

If the driving force is zero what happens?

Answer 15

No net movement

Question 16

Movement of ions between the ECF and ICF causes what?

Answer 16

Ionic current

Question 17

Ionic current is almost synonymous with what?

Answer 17

Conductance

Question 18

What 2 factors determine membrane potential?

Answer 18

Concentrations of ions across the cell membrane and permeabilities

Question 19

What eqn gives relation between the membrane potential and conc./permeabilities of ions?

Answer 19

Goldman

Question 20

What is an action potential?

Answer 20

Transient increase in sodium permeability; basic signal of the nervous system

Question 21

Describe the action potential phases

Answer 21

• Resting membrane potential is around -70mv, depolarization starts to occur and once the sodium coming in hits the threshold an AP is generated
• Depolarizing phase
• Overshoot
• Repolarizing phase
• Undershoot/hyperpolarizing phase

Question 22

What is the depolarizing phase?

Answer 22

When the membrane potential becomes less negative than resting membrane potential

Question 23

What is the overshoot?

Answer 23

When the inside of the cell becomes positive in respect to the outside of the cell for a brief moment

Question 24

What is the repolarizing phase?

Answer 24

Membrane potential returns to resting level

Question 25

What is the undershoot/hyperpolarizing phase?

Answer 25

When repolarizing, the membrane potential becomes slightly more negative than the resting membrane potential

Question 26

Describe the sodium channels

Answer 26

2 gates - activation gate and inactivation gate The activation gate is closed at resting but opens upon depolarization The inactivation gate is open at resting but slowly closes upon depolarization

Question 27

The act of the inactivation gate closing slowly upon depolarization - thus a delayed decline in sodium permeability - is known as what?

Answer 27

Sodium channel inactivation

Question 28

Describe the potassium channels

Answer 28

Just one gate, that is closed at resting and opens to let potassium out of the cell upon depolarization

Question 29

Does the potassium gate open when the sodium activation gate does?

Answer 29

No, the potassium gate is slower to open

Question 30

What is the absolute refractory period?

Answer 30

The time right after an AP has been generated that no amount of stimulus could cause another AP to be fired - Inactivation gates are closed

Question 31

What is the relative refractory period?

Answer 31

The time after the absolute refractory period where the cell is hyperpolarizing, and if the stimulus were large enough an AP could be generated, but the stimulus must be larger than usual

Question 32

What is accomodation?

Answer 32

When cell is held at depolarized level for a sustained manner - occurs bc inactivation gates of sodium close slowly and remain closed which causes an increased potassium conductance out of the cell and results in a net reduction in cell excitability

Question 33

Hyperkalemia

Answer 33

High potassium in ECF, can cause muscle spasms because the resting membrane potential is less negative = depolarized

Question 34

Hypokalemia

Answer 34

Low potassium in ECF hyperpolarizes the cell which makes the resting membrane potential more negative and makes it harder to fire an AP causing muscle weakness

Question 35

Hypokalemic periodic paralysis

Answer 35

Attacks occur suddenly and may be triggered after exercise, stress or a high carb meal - muscle weakness

Question 36

What does lidocaine do?

Answer 36

Blocks sodium channels and action potentials do not occur

Question 37

What properties of the axon determine the way APs propagate?

Answer 37

Time constant and length constant

Question 38

What is tau?

Answer 38

The shorter the tau, the faster the speed of the impulse propagation - thus you want low membrane resistance and capacitance

Question 39

What is lamda?

Answer 39

The longer the lamda, the less the loss of the signal will be and the farther down the axon the voltage will spread - thus you want a large diameter to lower the internal resistance

Question 40

What properties does myelination give?

Answer 40

Increases the membrane resistance and lowers the membrane capacitance thus increasing the conduction velocity - nodes of ranvier and saltatory conduction

Question 41

What happens due to multiple sclerosis?

Answer 41

Loss of myelin sheath, causes a decreased in lamda and membrane resistance and thus a loss in the signal, so failure to conduct APs

Question 42

What are the symptoms of multiple sclerosis?

Answer 42

Weakness in LE, numbness, paresthesia, blurred vision and pain with eye movements