Chapter 4 - Action Potential

Question 1

What happens in neuronal charge during action potential?

Answer 1

Membrane potential becomes positive
Rising phase: to 40 mV
Overshoot: inside of neuron positively charged
Falling phase: rapid repolarization to more negative than resting potential
Undershoot: restoration to resting potential
Lasts 2 milliseconds

Question 2

What happens when thumbtack enters skin?

Answer 2

1. Membrane of nerve fibers in skin stretches
2. Na+ permeable channels open
3. Na crosses membrane thru channels and attracts to negative charge
4. Na+ depolarizes membrane cytoplasmic (inside) surface, making less negative (called generator potential)
5. Depolarization reaches critical threshold causing action potential
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Question 3

How does depolarizing current affect AP generation?

Answer 3

Increased current increases rate of AP generation firing frequency
Maximum is 1000 Hz
Impossible to initiate another for 1 msec (absolute refractory period)
After absolute refractory period, in relative refractory period amount of current needed for another action potential is elevated above normal

Question 4

How does membrane repolarization happen?

Answer 4

Efflux of potassium ions

Question 5

What’s the formula for the amount of ionic current that will flow?

Answer 5

I ion = g ion (V membrane - E ion)

Cross-Membrane current = membrane conductance (membrane potential - charge)

Question 6

What is the Nernst equation?

Answer 6

E K = -80 mV

E Na = 62 mV