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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