ACTION POTENTIALS By: Heidi Hisrich.

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Presentation transcript:

ACTION POTENTIALS By: Heidi Hisrich

What is electrical potential? Difference in concentration of charges from one point to another (i.e. flashlight battery has potential of 1.5 V)

Also called “POLARIZED” Inside of membrane is more NEGATIVE and outside is more POSITIVE

RMP (Resting Membrane Potential) comes from this polarity RMP of the membrane of an axon is -70mV

Why it is negative Potassium has greatest effect on RMP because membrane is most permeable to potassium

Why it is negative (continued) Inside the cell are many anions (negative ions) that cannot leave Phosphates Sulfates Organic acids Proteins ATP RNA

Resting Potential Sodium is leaking in VERY slowly and potassium out LESS slowly (both try to reach equilibrium of concentration inside and outside the membrane) BUT… Sodium-Potassium pump works MUCH FASTER, compensating

Resting Potential (continued) Na/K pump pumps OUT 3 Na+ ions And pumps IN 2 K+ ions

Resting Potential (continued) The Na/K pump maintains the cell’s POLARITY or RMP at -70 mV by keeping the: OUTSIDE positive INSIDE negative

Then what? Neural stimulation! Neurons can be stimulated by: Chemicals Light Heat Mechanical distortion of the membrane

Triggers Depolarization It’s depolarization ANYTIME the membrane potential moves toward zero

Depolarization Na+ channels open Na+ rushes INTO cell Outside of cell becomes NEGATIVE and inside becomes POSITIVE

CAN LEAD to an Action Potential Only an action potential if it gets above zero

Action Potentials All or nothing—the nerve fires or it doesn’t

Right after nerve fires--repolarization Membrane becomes polarized again (RE-polarized) K+ channels open K+ rushes OUT OF the cell (to restore concentration equilibrium) Outside becomes NEGATIVE & inside POSITIVE

Return to resting potential To MAINTAIN polarization, the sodium-potassium pump must work CONSTANTLY!!!!

Maintaining resting potential takes WORK! It takes 70% of the energy requirements of the nervous system

Maintaining resting potential takes WORK! It takes 1/3 of the body’s total energy!

Learn more here! Crash Course in the Nervous System

So after a neuron FIRES, what happens? They have to send the message to the NEXT neuron! So now we’ll learn how that’s done… (continue with 2.2.2.)

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