Membrane Resting Potential & Action Potential

Question 1

What is resting membrane potential?

Answer 1

It is the electrical potential difference across a membrane

Question 2

What is the name of the electrical potential that counters the net diffusion of K+

Answer 2

The K+ equilibrium potential or the Nernst potential for K+

Question 3

What is the Nernst Potential?

Answer 3

It is the electrical potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane.

Question 4

What is the Nernst Potential Equation?

Answer 4

EMF (millivolts): +/- 61 log (concentration inside/concentration outside)
The sign of the potential is positive if the ion is negative and negative if the ion is positive

Question 5

What are the three factors that affect the equilibrium potential of membrane permeable to several different ions (Goldman equation)?

Answer 5

1) Concentration of the different ions on both the inside and outside of the cell
2) Permeability of the membrane to each ion
3) Polarity of the electrical charge of ions positive or negative

Question 6

Why is Vm (-86 mV) so close to Ek (-94 mV) compared to Ena (+61)?

Answer 6

The membrane is far more permeable to K+ than Na+

Question 7

What is the resting membrane potential for large nerve fibers (motoneurons)?

Answer 7

-90mV

Question 8

What is the resting membrane potential for small neurons of the nervous system?

Answer 8

-70 mV

Question 9

What factors affect the resting membrane potential? (3)

Answer 9

1) Diffusion of K+ and Na+
2) Permeability of ions through leak channels (more permeable to K+)
3) Na+/K+ Pump: creates more negativity inside

Question 10

What is an Action Potential?

Answer 10

It is a very rapid change in the membrane potential from “-“ to “+” values and returns back to the initial resting potential level.
It is an “ all-or-none” event, either it happens fully or not at all.
It propagates along the nerve fiber until it comes to the end of the fiber

Question 11

What are the functions of an Action potential? (3)

Answer 11

1) Transmitting Nerve signals: sensory info goes from periphery to CNS and motor info goes from CNS to the periphery
2) Rapid transmission over distance: speed of transmission depends on fiber size and whether or not it is myelinated
3) Encoding Information (neuronal language): The frequency of AP encodes info ( amplitude cannot change)

Question 12

How many stages are there to an action potential?

Answer 12

5, 
resting stage
depolarization
repolarization
afterpotential (undershoot)
back to resting stage

Question 13

At what membrane potential is the resting stage?

Answer 13

-90mV

Question 14

Define depolarization stage

Answer 14

-90 to 35 mV, 0.1 ms period (very fast)

Caused by the sudden opening of Na+ channels and the flow of Na+ ions into the cell

Question 15

Define Repolarization stage

Answer 15

35 mV to -90 mV
Na+ channels begin to close, Na+ ions stop flowing into the cell.
K+ channels begin to open, and K+ ions start to flow outside
Re-establishes the negative resting potential of the cell

Question 16

What is Afterpotential (hyperpolarization, undershoot)?

Answer 16

Less than -90 mV which is cause by K+ channels that remain open for a few milliseconds after repolarization of the membrane is reached.

Question 17

Define Back to resting stage

Answer 17

K+ channels close

Question 18

How many gates does the voltage-gated sodium channel have?

Answer 18

2 gates: 
activation gate (exterior side of the membrane)
Inactivation gate (interior side of membrane)

Question 19

What are the three states of the voltage-gated sodium channels?

Answer 19

Resting state: inactivation gate open, activation gate closed (no Na+)
Activated state: both gates open (opening threshold -70 mV to -50mV) (Na+)
Inactivated state: inactivation gate closed, activation gate open (happens when membrane potential increases over 0 mV (overshoot)) ( No Na+)

Question 20

How many gates do the voltage-gated potassium channel have?

Answer 20

1, on the interior side of the membrane

Question 21

How many states do the voltage-gated potassium channels have?

Answer 21

2, resting state ( gate closed)

slow activation state (gate open)

Question 22

Explain the Slow activation state (repolarization)

Answer 22

K+ channels are activated when the membrane potential increases above 0 mV, gates open slowly while the Na+ channels start to close. Potassium ions flow outside the cell which accelerates repolarization toward resting potential

Question 23

How did Dr. Ramachandran refer to mirror neurons?

Answer 23

He called them empathy neurons

Question 24

What is the threshold for initiation of an Action Potential?

Answer 24

it is the level of membrane potential at which the positive-feedback cycle is created (point of no return). Occurs when the number of sodium ions entering the nerve becomes greater than the number of potassium ions leaving the nerve
about - 65mV for a nerve with Vm= -90

Question 25

What can cause the initial increase in membrane potential to reach the threshold?

Answer 25

Mechanical stimulation
Chemical stimulation
Electrical stimulation

Question 26

True or False. The amplitude of an AP is dependent on the intensity of the stimulus that evokes it.

Answer 26

False, it is independent.

The frequency of firing however is dependent on the intensity of the stimulus

Question 27

What is the Absolute refractory period?

Answer 27

It is a period during which another AP cannot occur as long as the membrane is still depolarized from the preceding AP

Question 28

Why does the Absolute refractory period occur?

Answer 28

Because Na+ channels are inactivated and the membrane has to return near original resting potential to allow inactivation gates to reopen

Question 29

What is the Relative Refractory Period?

Answer 29

It is the period that immediately follows an absolute refractory period during which a new AP can occur if the stimulus is strong enough.

Question 30

Why does the relative refractory period happen?

Answer 30

Some Na+ channels start to go back to their resting state and others are still inactivated. K+ channels are still open and the membrane is hyperpolarized

Question 31

Myelin is produced as an extension of what cells?

Answer 31

Schwann cells in PNS

Oligodendrocytes in CNS

Question 32

What is a myelinated nerve fiber?

Answer 32

Nerve fiber whose axon is surrounded by myelin sheaths. Ions cannot significantly flow through myelin sheaths which thus insulates the nerve fiber

Question 33

What is saltatory conduction?

Answer 33

APs can only occur at the node of Ranvier and are conducted from node to node. It conserves energy for axons. Conduction velocity varies from 0.25 m/s in unmyelinated fibers to as great as 120 m/s in large myelinated fibers.

Question 34

What is Multiple Sclerosis (MS)?

Answer 34

It is an immune-mediated inflammatory disease that causes the demyelination of the CNS
symptoms include muscle weakness, loss of sensation, death