Neurons

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How is resting potential maintained?

Ion Distribution

Slide 11

How is resting potential maintained?

At rest, the sodium gates are closed.

Membrane is 50 times more permeable to K+ ions causing them to “leak” out.

This causes outside of membrane to have an abundance of + charges compared to inside. The inside of the membrane is negative compared to the outside. This is helped by the (-) proteins etc.

The “sodium-potassium” pump pulls 2 K+ ions in for 3 Na+ ions sent out. This further creates a charge difference!!

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Action Potential

The mechanism by which neurons send impulses. They are comprised of electrical signals generated at the soma and moving along the axon toward the end opposite the soma (motor neurons)

Action potentials occur in two stages:

Depolarization

Repolarization

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Depolarization in an action potential

When the neuron is excited past its “Threshold” the following events occur:

Sodium ions (Na+) rush into the axon.

This neutralizes the negative ions inside.

The inside of the axon becomes temporarily (+) while the outside becomes temporarily (-). The reversal of charge is known as “depolarization”

Nearby Sodium (Na+) channels open to continue the depolarization.

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Slide 15

Let’s Have a look.

http://www.mcgrawhill.ca/school/booksites/biology/student+resources/toc/unit+4+homeostasis+maintaining+dynamic+equilibrium/chapter+12+the+nervous+system/cool+stuff+to+see+and+do/movie+channel+behaviour.php

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Repolarization

This is the restoring of the (+) charge on the outside of the axon and (-) on the inside.

Potassium gates open and potassium floods out.

This generates positive charge on the outside of membrane.

Sodium Channels Close (no + charges can get inside)

The Sodium/Potassium pump rapidly moves Sodium out of the cell.

Further creates the (+) charge outside with a (-) charge inside.

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Slide 18

Refractory Period

Brief period of time between the triggering of an impulse and when it is available for another.

NO NEW action potentials can be created during this time.