02 | RMP and AP

Question 1

Define: RMP

Answer 1

difference in electrical charge between the inside and outside of a cell (written: inside relative to outside)

Question 2

Factors that affect RMP

Answer 2

• E(K)
• E(Na)
• g(K)
• g(Na)
• Na/K ATPase

Question 3

3 requirements for stable Vm

Answer 3

1. Electrical balance
2. Osmotic balance
3. No net flow of ions

Question 4

E(Ca) =

Answer 4

+150 mV

Question 5

Amount of current generated depends on…

Answer 5

driving force

Question 6

Formula: driving force

Answer 6

= Vm - E(ion)

Question 7

Define: conductance

Answer 7

How easily electrical charge moves across the membrane

Question 8

Conductance depends on…

Answer 8

1. If channel is opened or closed

2. Channel density

Question 9

Define: permeability

Answer 9

How easily the particle mass moves across the membrane

Question 10

What is Nernst equation used to calculate?

Answer 10

Equilibrium potential of the ion

Question 11

What does the Goldman equation calculate?

Answer 11

Membrane potential

Question 12

What is the limitation to the Goldman equation?

Answer 12

Only applies to steady state (aka Vm not changing) (aka no depolarization/hyperpolarization)

Question 13

Na/K ATPase contributes __ mV to the Vm

Answer 13

-6 mV

Question 14

How many Na and K ions are moved per cycle of Na/K ATPase?

Answer 14

3 Na out, 2 K in (net negative)

Question 15

Define: AP

Answer 15

Explosive change in electrical activity (sudden change in Vm)

Question 16

5 things that can induce AP

Answer 16

1. Electrical change
2. Chemical
3. Mechanical
4. Light
5. Temperature

Question 17

What are the 4 types of currents involved in an AP?

Answer 17

1. Capacitive current
2. Leak current
3. Early inward current (Na)
4. Late outward current (K)

Question 18

What is capacitive current?

Answer 18

The spike in current when membrane potential initially changes. This is because the membrane acts like a capacitor. The current can be ignored during analysis.

Question 19

What is leak current? Which ion is responsible for it?

Answer 19

Current that is always present due to flow of K ions.

Question 20

What did ion manipulation find out about AP current?

Answer 20

• Na replaced with choline — no driving force for Na
• Only outwards current was observed
• ∴ Na must be responsible for the inward current

Question 21

What is the unit for current?

Answer 21

mA/cm^2

Question 22

What does TTX block?

Answer 22

v-gated Na channels

Question 23

What does TEA block?

Answer 23

v-gated K channels and K leak channels

Question 24

Magnitude of early inward current depends on…

Answer 24

Vm (because this determines the driving force for Na)

Question 25

Define: reversal potential

Answer 25

The Vm at which the ion’s flow changes direction

Question 26

What does “delayed rectifier” mean?

Answer 26

Delayed = does not change right away

Rectifier = current increases during depolarization, but hot hyperpolarization (“rectifies” Vm back to resting)

Question 27

Define: inactivation (in terms of current flow)

Answer 27

The fall of Na current

Question 28

Absolute refractory period is due to…

Answer 28

inactivation of Na channels

Question 29

Effects of Ca

Answer 29

1. Enhance depolarization
2. Inhibit depolarization
3. Hypercalcemia

Question 30

How does Ca inhibit depolarization?

Answer 30

open Ca-activated K channels

Question 31

Ca-induced AP usually found in…

Answer 31

• cardiac muscle
• invertebrate neurons
• mammalian cerebellar Purkinje cells

Question 32

Na is usually used to depolarize the soma, while Ca is used to depolarize ___

Answer 32

dendrites

Question 33

Why does hypercalcemia result in decreased excitability?

Answer 33

Ca-induced Na channel block

Question 34

Summation usually occurs at…

Answer 34

axon hillock

Question 35

Common examples of graded potentials (rather than AP)

Answer 35

• Light hitting eye
• Sound wave in ear
• Pressure on skin
  (things where magnitude matters)