1/29: Nervous System Overview & Action Potential II

Question 1

What are the two refractory periods that neurons have?

Answer 1

1. Absolute refractory period
2. Relative refractory period

Question 2

What happens during the time of an absolute refractory period?

Answer 2

It is impossible for the cell to fire another action potential
*due to the all-or-none activation and the voltage-gated Na+ channels closed inactivation gates

Question 3

What is happening during the time of relative refractory period?

Answer 3

A larger than normal EPSP can elicit an action potential

Question 4

When does the relative refractory period begin? and end?

Answer 4

Once the voltage gated Na+ channel starts to reset to the resting state, and ends when they are all reset

Question 5

What happens in hyperkalemia when 3.5<[K]ECF<6mM?

Answer 5

• increaes membrane excitability
• depolarizes Vm moving closer to threshold

Question 6

What happens in hyperkalemia when [K]ECF>6mM?

Answer 6

• reduces membrane excitability
• depolarizes membrane and cause inactivation of voltage gated Na+ channels

Question 7

What occurs in hypokalemia?

Answer 7

• Reduces membrane excitability
• Hyperpolarizes membrane further from threshold

Question 8

What does hyper and hypocalcemia due to membrane excitability?

Answer 8

Hypercalcemia: reduces membrane excitability
Hypocalcemia: increases membrane excitability

Question 9

Simultaneous recordings show that each section of an axon is experiencing _______

Answer 9

A different phase of the action potential

Question 10

What are the 5 steps of the depolarized section of an axon?

Answer 10

1. A graded potential above threshold reaches the trigger zone
2. Voltage-gated Na+ channels open and Na+ enters the axon
3. Positive charge flow into adjacent sections of the axon by local current flor
4. Local current flow from the active region causes new sections of the membrane to depolarize
5. The refractory period prevents backwards conduction. Loss of K+ from the cytoplasm repolarizes the membrane

Question 11

What does the myelin of an axon function as?

Answer 11

An insulator

Question 12

What is saltatory conduction of an action potential?

Answer 12

AP jumps form node to node

Question 13

What are the benefits of a myelinated axon?

Answer 13

• speeds up conduction velocity of action potential
• conserves axon energy

Question 14

What happens to the velocity of an AP if axons have myelin?

Answer 14

Velocity increases

Question 15

What happens to the conduction velocity of an ap when the axonal diameter increases?

Answer 15

Velocity increases

Question 16

When an axon is demyelinated, what does the cause in the CNS? PNS?

Answer 16

CNS - multiple sclerosis
PNS - Guillain-Barre syndrome