Lecture 2 Flashcards
Ionic Channels
specific to ionic size and charge
Size Exclusion
sodium channel can exclude calcium/ potassium ions due to diff molecule size
Charge Exclusion
Interior of channel will be lined with charged amino acids, will prevent ions from crossing
Leak Channels
always open
some K+ and Cl- channels
Gated Channels
closed until stimulus opens
Ligand Gated Channels
Remain closed until proper ligand binds, and stays open until its removed
Nicotinic receptors in skeletal m
2nd Messenger Gated Channels
open when 2nd messenger is around, closes when removed
Ca2+ channels in smooth m
Voltage Gated Channels
closed until membrane potential hits certain value
stays open while in certain range
Na+ channels in mm
Ionic Movement
Equilibrium Potential
ions move down gradient until certain charge is met that stops the movement
move in response to conc and charge
Nerst Equation
calculate equilibrium potential
Resting Membrane Potential
charge difference across cell membrane due to conc gradients of permeant ions
Resting Membrane Potential ranges and averages
- 20 to -100 mV
- 70 in neurons, -90 in skeletal and cardiac mm
Action Potentials
rapid changes in membrane potentials
Stages of Action Potential
RMP Depolarization Overshoot Repolarization Hyperpolarization RMP
Na K ATPase
necessary for RMP
3 Na+ out, 2 K+ in
makes cell more negative
Threshold
-60 mV
if reached, action potential must occur
voltage gated Na channels open- causes depolarization
Overshoot
due to rapid influx of Na+
+35 mV
inactivation gates close, no Na+ movement
K+ channels open
Repolarization
Na slows, K rises
positive charges leave cell
Hyperpolarization
membrane becomes more negative than RMP
Hyperkalemia
too much K
less of a gradient, more positive RMP
Hypokalemia
not enough K
higher gradient, more negative RMP
Refractory Periods
from cell’s inability to depolarize- channels dont reset
Absolute RP
No AP
activation gate of Na not closed
Relative RP
need greater than normal stimulus
K flux hyperpolarizes cell, harder to get to threshhold
