Ch. 12 Nervous System c
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Describe resting membrane potential for a neuron
The Sodium-potassium pump keeps a high concentration of Na outside of the cell and a high concentration of K inside of the cell. It does this to keep the inside of the cell at a negative charge of about -70mv. The negatively charged particles in ICF also keeps K attracted in.
What are graded potentials?
Also called local potentials, they are short-lived and short-distanced potentials. They vary with the strength of stimulus and get weaker as it goes farther.
What is the relation of a graded potential to an action potential?
If a graded potential arrives at and depolarizes the area of the trigger zone (basically the axon hillock) enough, it can open the gates there and cause a real signal, aka an action potential down the axon.
Remind yourself, What is an action potential?
A quick up-and-down shift in the cell membrane voltage.
What are the six steps in sending an action potential down an axon? (similar to a muscle)
- 1. Incoming pulse slightly depolarizes the potential
- 2. Gates at the trigger zone will open if charge reaches threshold, the minimum charge to start an action potential (-55mv). If it does not meet this it will just revert back to RMP. This is called the all-or-none principle
- 3. When gates open, Na will rush into the axon, causing the charge to go from -55 to +35mv. This causes nearby gates to do the same thing, thus carrying the signal down
- 4. When it reaches this peak, the Na channels will close and K channels will open allowing K to rush out (repolarization).
- 5. K gates stay open longer, causing hyperpolarization or the drop of the membrane potential to too low (about -72mv versus the normal -70mv)
- 6. The sodium-potassium pump brings this back to normal by pumping Na out and K back in at a rate of 3Na:2K.
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