Nervous System 2 - Action Potentials

Question 1

What Graded (Passive) potentials initiated by?

Answer 1

A stimulus that is either sensory or chemical

Question 2

What is meant by Graded in Graded (Passive) potentials?

Answer 2

The magnitude can vary with the strength of the stimulus

Question 3

What kind of polarization can Graded potentials give?

Answer 3

They can Depolarizing or Hyperpolarizing

Question 4

How does the strength of the stimulus affect the membrane potential in Graded (Passive) Potentials?

Answer 4

A stronger stimuli will increase the Membrane potential more than a smaller stimuli. So the stronger a stimulus, the larger the passive potential

Question 5

What do Passive Potentials arise from?

Answer 5

Current that flow into the membrane

Question 6

What happens as the current moves down the axon in Passive Potentials?

Answer 6

It loses strength and falls in amplitude

Question 7

What does Passive spread of current depend on?

Answer 7

It depends on the dendrite or axons resistance to flow of current

Question 8

How do dendrites or axons affect the spread of current?

Answer 8

Smaller dendrite or axons have a higher resistance so current flows with difficulty down them

Question 9

What are the characteristics of Nerve Action Potentials?

Answer 9

They are Rapid, transient and result in a large change in membrane potential resulting in a reversal fo polarity

Question 10

What does a Nerve Action Potential consist of?

Answer 10

Rapid depolarization followed by rapid repolarization of the membrane

Question 11

What is another name for an Action Potential?

Answer 11

A spike

Question 12

What is a Spiking neuron?

Answer 12

One that is firing APs

Question 13

What membrane potential must be met to produce an action potential?

Answer 13

Vm must reach threshold

Question 14

What is Threshold?

Answer 14

The membrane potential at which a spike is initiated

Question 15

Can graded potentials reach threshoid?

Answer 15

Graded potentials MAY bring Vm to threshold

Question 16

How does the strength of the stimulus affect an membrane potential in an action potential?

Answer 16

As long as the stimulus reaches threshold the Membrane potential will reach the same amplitude every time

Question 17

What does Threshold trigger in terms of channels?

Answer 17

Threshold triggers rapid opening of sodium channels, follow by slow closing of sodium channels and the slow opening of potassium channels

Question 18

What is the order of the steps in membrane potential?

Answer 18

• Resting potential
• Rising Phase
• Overshoot
• Falling Phase
• Undershoot

Question 19

What is the Equilibrium potential of Sodium?

Answer 19

+52mV

Question 20

What does the transient inward current represent when the membrane is depolarized in an action potential?

Answer 20

The movement of sodium

Question 21

What does the Delayed outward current represent when the membrane is depolarized in an action potential?

Answer 21

The movement of K+

Question 22

What happens to the movement of sodium as the membrane potential is depolarized closer to +52mV?

Answer 22

Because the membrane potential is reaching the equilibrium potential of Na+ the driving force for Na+ to move into the cell decreases and the transient inward current decreases and eventually inverts as sodium moves outward

Question 23

What happens to the movement of Potassium as the membrane potential is depolarized closer to +52mV?

Answer 23

The driving force of potassium increases as the membrane potential moves farther from its equilibrium

Question 24

What does TTX (Tetrodotoxin) do?

Answer 24

Block voltage gated Na+ channels

Question 25

What does TEA (Tetraethylammonium) do?

Answer 25

Blocks voltage gated K+ channels

Question 26

How does TTX (Tetrodotoxin) affect current in an action potential?

Answer 26

It prevents the inward current of sodium

Question 27

How does TEA (Tetraethylammonium) affect current in an action potential?

Answer 27

It prevents the outward current of K+

Question 28

How does Conductance of channels change during an action potential?

Answer 28

Sodium channels increase conductance with the action potential and decrease conductance with the action potential
Potassium channels are delayed by time and conductance is prolonged

Question 29

How can ions leak out of the axon?

Answer 29

Through leakage channels

Question 30

What are leakage channels?

Answer 30

Channels through which K+ and Na+ can leak out of which are distinct from the voltage gated channels

Question 31

What is the Refractory period?

Answer 31

The time during which the axon is resistant to generating a spike

Question 32

What does a Refractory period result from?

Answer 32

Na+ channels being inactivated and unavailable

Question 33

Where are Sodium channels concentrated?

Answer 33

At nodes of ranvier

Question 34

What is the function of the Myelin sheath?

Answer 34

It reduces current loss across the membrane and acts as an electrical insulator

Question 35

How do scorpion toxins affect action potentials?

Answer 35

They contain many active peptides that bind to Na+ channels to slow their inactivation and prolong their openings

Question 36

How do many Anesthetic work?

Answer 36

They work by blocking voltage dependent Na+ channels which block action potentials or by hyperpolarizing the membrane by increasing Cl- influx

Question 37

What occurs in multiple sclerosis?

Answer 37

The loss of myelin sheath slows spike conduction to eventually impair muscle contraction