Exam 2 - Lecture 21 (Membrane Potential 2)

Question 1

Why is there an INflux of Na+ when Na+ channels open?

Answer 1

Because [Na+] is HIGH outside of the cell

Question 2

Why is there an OUTflux of K+ when K+ channels open?

Answer 2

Because [K+] is LOW outside of the cell

Question 3

What are the 3 steps in CNS recognition of sensory stimulus?

Answer 3

1. RMP
2. Sensory stimulus generates receptor potential
3. Receptor potential goes over the threshold
4. AP

Question 4

What are the 2 phases of an AP?

Answer 4

1. Rising phase

2. Falling phase

Question 5

What is the state of VG Na+ channels when at RMP before AP?

Answer 5

resting

Question 6

What is the state of VG Na+ channels when at threshold?

Answer 6

activated (channels open)

Question 7

What is the state of VG Na+ channels when at peak?

Answer 7

Inactivated (channels close)

Question 8

What is the state of VG Na+ channels when at RMP after AP?

Answer 8

De-inactivated (hyperpolarization)

Question 9

Hyperkalemia leads to _____ (depolarization or hyperpolarization). What happens?

Answer 9

depolarization; K+ rush into cell, MP less negative

Question 10

Hypokalemia leads to _____ (depolarization/hyperpolarization). What happens?

Answer 10

hyperpolarization; low K+ outside, so inside more negative, lowers RMP

Question 11

Generating APs is much easier under _____ (hyperkalemia/hypokalemia).

Answer 11

hyperkalemia

Question 12

What causes hyperpolarization?

Answer 12

K+ outflux is still occurring after Na+ channels close, making RMP more negative

Question 13

What does the Nernst equation calculate?

Answer 13

Generates equilibrium potential voltage

Question 14

What is equilibrium potential?

Answer 14

Ions move freely according to their [ ] gradients

Question 15

What effect does tetrodotoxin and lidocaine have on axons?

Answer 15

Prevent generation of APs by blocking VG Na+ channels

Question 16

Where is tetrodotoxin found?

Answer 16

puffer fish

Question 17

How do more stimuli affect APs?

Answer 17

More stimuli = higher frequency of APs

NOTE: stronger stimulus does NOT lead to stronger AP

Question 18

What are 3 unique properties of APs that reflect the properties of VG Na+ and K+ channels?

Answer 18

1. All or none
2. Refractory period
3. APs run in one direction

Question 19

What is the refractory period?

Answer 19

Time after an AP when the plasma membrane is unresponsive to new stimuli (cannot generate a new AP)

Question 20

What is the all or none concept?

Answer 20

Majority of VG Na+ and K+ channels only respond when the threshold is reached

Question 21

What is the absolute refractory period?

Answer 21

Period during which VG Na+ channels are in inactivated state and AP cannot be generated

Question 22

What is the relative refractory period?

Answer 22

Period when a stronger than normal stimulus is needed to elicit APs
(Hyperpolarization)

Question 23

Why do APs only run in one direction?

Answer 23

Because of the refractory period (PM immediately distal to an AP is still under the refractory period)

Question 24

What direction do APs run?

Answer 24

periphery –> CNS (away from stimulus)

Question 25

Are APs all the same strength?

Answer 25

Yes