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82 Cards in this Set
- Front
- Back
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What is the diffusion potential? |
The electronegative potential between the inside and outside of a cell |
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What is the potential difference required to block potassium diffusion to the exterior of the cell? |
94 mV, negative inside the cell |
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What keeps potassium from freely flowing out of the cell to equalize the concentration gradient? |
The electrical gradient that becomes more negative when positively charged ions like K+ leave the cell |
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What is the electrical potential required to block sodium ions from diffusing into the cell? |
61mV (positive to the inside of the cell) |
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What is the equation for the Nernst potential of an ion? |
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What is the Goldman-Hodgkin-Katz equation? |
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How does the Goldman-Hodgkin-Katz equation differ from the Nernst potential equation? |
It accounts for the permeability (and thus influence) of each ion |
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What three ions are used to calculate the Goldman-Hodgkin-Katz equation? |
K+, Na+, Cl- |
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Which two ions are primarily responsible for signal transmission in neurons? |
Sodium and potassium |
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Relatively speaking, how many ions must shift to the outside of the cell to change the membrane potential? |
Very, very few |
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What term describes the Na+/K+ pump's creation of a deficit of positive ions on the inside of the cell? |
Electrogenic |
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What is the [Na+] inside the cell? |
14 mEq/L |
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What is the [Na+] outside the cell? |
142 mEq/L |
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What is the [K+] outside the cell? |
4 mEq/L |
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What is the [K+] inside the cell? |
140 mEq/L |
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What is the ratio of Na+ inside/Na+ outside? |
0.1 |
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What is the ratio of K+ inside/K+ outside? |
35 |
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What other ion are K+ leak channels permeable to? |
Na+ |
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How much more permeable to potassium than sodium are K+ leak channels? |
100x |
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What three factors influence the nerve's resting potential? |
K+ diffusion Na+ diffusion K+/Na+ pump activity |
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What is the nerve's overall resting membrane potential? |
-90mV |
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How much of the nerve's resting membrane potential is contributed by the sodium-potassium pump? |
About -4 mV |
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What are action potentials? |
Rapid changes in the membrane potential that spread rapidly along the nerve fiber membrane |
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What is the stage before the action potential begins called? |
Resting stage |
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What are the two stages of the nerve action potential? |
Depolarization and repolarization |
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What ion does the membrane become permeable to during depolarization? |
Na+ |
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What does the membrane potential become during depolarization? |
+35 in large nerves Zero-ish in smaller/many CNS nerves |
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What changes occur between depolarization and repolarization? |
Sodium channels begin to close Potassium channels open more than normal |
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What ion diffuses to restore the normal resting membrane potential of the nerve in repolarization? |
Potassium |
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What three types of channel does K+ travel through? |
Na+/K+ pump channels K+ leak channels Voltage-gated potassium channel |
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What is the outer gate of the voltage-gated sodium channel called? |
Activation gate |
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What is the inner gate of the voltage-gated sodium channel called? |
Inactivation gate |
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During the resting phase, which gate of the voltage-gated sodium channel is closed? |
Activation gate |
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What voltage triggers the voltage-gated sodium channel to open? |
Usually -50 to -70 |
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What happens when the voltage-gated sodium channel reaches its trigger voltage? |
It causes a sudden conformational change in the activation gate, flipping it all the way to the open position |
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When the voltage-gated sodium channel is in its activated state, how much more permeable to sodium is the membrane? |
500-5000 times more |
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What triggers the inactivation gate of the voltage-gated sodium channel to close? |
The same voltage trigger that opened the activation gate; however, the inactivation gate is slower, so it allows a large influx of sodium before it closes. |
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What causes the voltage-gated sodium channel's inactivation gate to reopen? |
The membrane potential's return to its original resting level |
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Can the voltage-gated sodium channel reopen before the nerve fiber repolarizes? |
No; inactivation gate will not reopen until this happens |
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When, in relation to the voltage-gated sodium channels, do the voltage-gated potassium channels open? |
Right when the sodium channels are beginning to close due to inactivation |
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At what point do the voltage-gated potassium channels close? |
After the membrane potential returns to its low negative value |
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What is the calcium ion concentration gradient? |
Almost 10,000x |
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What is the major function of voltage-gated calcium channels? |
Contribute to the depolarizing phase of the action potential of certain cells |
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How fast (relatively speaking) are voltage-gated calcium channels? |
Very slow (10-20x slower than sodium channels) |
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What are alternate names for calcium and sodium channels? |
Calcium: slow channels Sodium: fast channels |
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Calcium and sodium both play a role in depolarization. How do these roles differ? |
Calcium: provides sustained depolarization with slow channels Sodium: initiates action potentials with fast channels |
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What type of cells have numerous calcium channels? |
Cardiac and smooth muscle |
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How does a deficit of calcium affect sodium channels? |
It profoundly affects the threshold for the sodium channels; they need very little increase in voltage to open and the nerve becomes highly excitable |
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How low does calcium need to fall in order to cause spontaneous discharge of peripheral nerves/tetany? |
50% of normal value |
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What is the usual threshold for an action potential to develop? |
-65mV |
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What is a nerve or muscle impulse? |
The transmission of the depolarization process along a nerve or muscle fiber |
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If the conditions are ideal, how far down the fiber membrane does the depolarization travel? |
Over the entire membrane, or not at all; no intermediate distance travelled |
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How are sodium and potassium ions returned to their original location inside/outside the cell after they diffuse in/out during the action potential? |
Na+/K+ pump |
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How does the Na+/K+ pump activity relate to the concentration of sodium ions inside the cell? |
Increases at a rate in proportion to the third power of the [Na+] - so if the sodium doubles, the pump works eightfold. |
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What causes a plateau during depolarization? |
1. Slow calcium channels 2. Voltage-gated potassium channels being slower than usual to open (delays the return of the low negative voltage) |
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In what tissues do repetitive self-induced discharges occur? |
1. The heart (beat) 2. Most smooth muscle (peristalsis) 3. Many CNS neurons (rhythmical control of breathing) |
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What is the 'resting' membrane potential in the pacemaker cells of the heart? |
-60 to -70mV |
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Why is the resting membrane potential less negative in the pacemaker cells of the heart? |
That way the sodium and calcium channels do not fully close; even at their most negative, there is continued inward Na+/Ca2+ flow, which restarts the increased voltage - increased permeability - increased ion flow - action potential cycle all over again. |
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Why does the membrane of the heart control center not depolarize immediately after it has become repolarized? |
Near the end of each action potential, and continuing for a short period thereafter, the membrane becomes more permeable to potassium ions; membrane becomes hyperpolarized and takes a moment to shift away the extra K+. |
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The axon is filled with what viscous intracellular fluid? |
Axoplasm |
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What lipid substance does the Schwann cell membrane contain? |
Sphingomyelin |
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How does sphingomyelin affect conduction? |
It's an excellent insulator; decreases ion flow by 5000-fold |
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How long is each node of Ranvier? |
2-3 micrometers |
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What is saltatory conduction? |
Action potential "jumps" from node to node along the myelin sheath |
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What are the advantages of saltatory conduction? |
5-50x faster Conserves energy for the axon |
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How does saltatory conduction conserve energy? |
Uses far less ion diffusion and requires much less metabolism for re-establishing concentration gradients |
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What is the velocity of action potential conduction in small unmyelinated fibers? |
0.25 m/sec |
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What is the velocity of action potential conduction in large myelinated fibers? |
100 m/sec |
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What three ways can sodium diffusion (and thus an action potential) be encouraged in nerves? |
Mechanical disturbance of the membrane Chemical effects on the membrane Passage of electricity through membrane |
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What are weak membrane potential disturbances at a particular location called? |
Acute local potentials |
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What are acute local potentials that fail to elicit an action potential called? |
Acute subthreshold potentials |
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What is the primary cause for the refractory period in a fiber? |
The sodium channel remains inactivated until the membrane potential returns to its original level |
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What do we call factors that decrease membrane excitability? |
Membrane-stabilizing factors |
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What category of drugs are important membrane-stabilizing factors? |
Local anesthetics |
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How do most local anesthetics work? |
Directly on the activation gates of sodium channels, making it more difficult for them to open |
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At what point will a locally anesthetized nerve no longer transmit impulses? |
When the ratio of action potential strength to excitability threshold drops below 1 |
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Where are most ligand-gated channels found? |
On the outside of the cell (extracellular ligand-gated) |
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Where do you find mechanically-gated channels? |
Sensory areas - touch, sound waves in ears, etc |
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What is the absolute refractory period? |
Period when Na+ channels are closed (which lasts until potential is back down to baseline)
NO action potential possible |
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What is the relative refractory period? |
"Overshoot" period where potential is farther away from threshold than at baseline and action potential is much harder to generate |
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What corrects the hyperpolarization caused by K+ channel 'overshoot'? |
Na+ leaking back in |
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How does insulin "drive" K+ into the cells? |
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