Exam 2 - Lecture 21 (Membrane Potential 2) Flashcards
Why is there an INflux of Na+ when Na+ channels open?
Because [Na+] is HIGH outside of the cell
Why is there an OUTflux of K+ when K+ channels open?
Because [K+] is LOW outside of the cell
What are the 3 steps in CNS recognition of sensory stimulus?
- RMP
- Sensory stimulus generates receptor potential
- Receptor potential goes over the threshold
- AP
What are the 2 phases of an AP?
- Rising phase
2. Falling phase
What is the state of VG Na+ channels when at RMP before AP?
resting
What is the state of VG Na+ channels when at threshold?
activated (channels open)
What is the state of VG Na+ channels when at peak?
Inactivated (channels close)
What is the state of VG Na+ channels when at RMP after AP?
De-inactivated (hyperpolarization)
Hyperkalemia leads to _____ (depolarization or hyperpolarization). What happens?
depolarization; K+ rush into cell, MP less negative
Hypokalemia leads to _____ (depolarization/hyperpolarization). What happens?
hyperpolarization; low K+ outside, so inside more negative, lowers RMP
Generating APs is much easier under _____ (hyperkalemia/hypokalemia).
hyperkalemia
What causes hyperpolarization?
K+ outflux is still occurring after Na+ channels close, making RMP more negative
What does the Nernst equation calculate?
Generates equilibrium potential voltage
What is equilibrium potential?
Ions move freely according to their [ ] gradients
What effect does tetrodotoxin and lidocaine have on axons?
Prevent generation of APs by blocking VG Na+ channels
Where is tetrodotoxin found?
puffer fish
How do more stimuli affect APs?
More stimuli = higher frequency of APs
NOTE: stronger stimulus does NOT lead to stronger AP
What are 3 unique properties of APs that reflect the properties of VG Na+ and K+ channels?
- All or none
- Refractory period
- APs run in one direction
What is the refractory period?
Time after an AP when the plasma membrane is unresponsive to new stimuli (cannot generate a new AP)
What is the all or none concept?
Majority of VG Na+ and K+ channels only respond when the threshold is reached
What is the absolute refractory period?
Period during which VG Na+ channels are in inactivated state and AP cannot be generated
What is the relative refractory period?
Period when a stronger than normal stimulus is needed to elicit APs
(Hyperpolarization)
Why do APs only run in one direction?
Because of the refractory period (PM immediately distal to an AP is still under the refractory period)
What direction do APs run?
periphery –> CNS (away from stimulus)
Are APs all the same strength?
Yes
