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Resting Membrane Potential
and Action Potential
Resting Membrane Potential and Action Potential
Positive outside
Positive outside
Negative inside
At rest, neuron is said to be polarized
How does a neuron become polarized?
Sodium-potassium pump
Resting Membrane Potential and Action Potential
At rest, neuron is said to be polarized
Net loss of positive charge from inside cell
Makes inside of cell negative in relation to outside
Sodium-Potassium Pump
For every 3 Na+ ions pumped out only 2 K+ ions are pumped in
Pump maintains resting membrane potential (RMP) at -70mV
High [K ]+
High [Na ]+
Action Potential
Changes to sodium channels and potassium
channels produce an action potential
Sodium channels open allowing Na+ ions to rush in
High [K ]+
High [Na ]+
Step 1:
Action Potential
Causes depolarization (inside neuron positively charged)
Sodium channels close and potassium channels open
High [K ]+
High [Na ]+
Action Potential
Step 2:
K+ ions rush out of neuron so inside of neuron becomes negative once again - repolarizationIMore negative than -70mV (undershoot - hyperpolarized)
Step 3:
High [K ]+
High [Na ]+
Action Potential
Na+/K+ pump restores resting membrane potential (RMP)
of neuron [-70mV]
Action potential propagates (moves) down axon
as wave of depolarization
As wave passes resting membrane potential is restored
Action Potential
Myelinated axons are able to increase speed of transmission
Depolarization occurs only at nodes of Ranvier
Nodes of Ranvier
Action Potential
Explains how an action potential moves within a neuron
However, for nervous system to work, neurons must communicate with one another
Myelinated 12-120 m/sec
Speed Comparison
Action Potential Velocity
Unmyelinated 0.2-2 m/sec
Action Potential
Homework
Read pgs. 523-526 Do Q#1-3, 5a pg. 529