Term
No threshold
Passive, decremental conduction
Size graded
Chemical, mechanical stimulus
Polarity inside negative
Other features
Not self-regenerating
Does not propagate
No refractory period
Temporal & spatial summation
What kind of action potential? |
|
Definition
|
|
Term
Threshold
Active, all-or-none conduction
All-or-none, same amplitude
Electrical stimulus
Polarity inside positive
Other features
Self-regenerating
Propagates
Refractory period
No Temporal & spatial summation |
|
Definition
|
|
Term
| An ??? is a change in the voltage of the membrane potential that causes it to go from its negative resting state to a positive value for a very brief time. |
|
Definition
|
|
Term
| What are the characteristics of an action potential? |
|
Definition
• Resting Level
• Threshold
• Rising phase
• Overshoot
• Peak
• Repolarization
• After-hyperpolarization (Positive afterpotential) |
|
|
Term
| The depolarization and rising phase of the action potential can be attributed to the increase in ??? |
|
Definition
| Increase in Na+ conductance |
|
|
Term
| The repolarization phase can be attributed to both the ??? and the slower ???. |
|
Definition
| Decrease in Na+ conduntance; Increase in K+ conductance |
|
|
Term
| • Decrease in gK - While the after-hyperpolarization is due to the sustained increase of ???, it decreases eventually to returnthe membrane potential to resting levels. |
|
Definition
|
|
Term
| The process of making the membrane potential less negative. |
|
Definition
|
|
Term
| The process of making the membrane potential more negative. |
|
Definition
|
|
Term
| The flow of positive charge into the cell, depolarizing the membrane potential. |
|
Definition
|
|
Term
| The flow of positive charge out of the cell, hyperpolarizing the membrane potential. |
|
Definition
|
|
Term
| The membrane potential at which occurence of the action potential is inevitable. This is usually less negative than the RMP. |
|
Definition
|
|
Term
| That portion of the action potential where the membrane potential is positive. |
|
Definition
|
|
Term
| That portion of the action potential, following repolarization, where the membrane potential is actually more negative that it is at rest. |
|
Definition
| Undershoot or hyperpolarization afterpotential |
|
|
Term
| A period during which another normal action potential cannot be elicited in an excitable cell. |
|
Definition
| Refractory period (absolute or relative) |
|
|
Term
| An action potential at one site causes depolarization at adjacent sites, bringing those adjacent potential from one site to the next is termed? |
|
Definition
| Non-decremental Propagation |
|
|
Term
| An action potential either occurs or does not occur. If an excitable cell is depolarized to threshold in a normal manner, then the occurenc of an AP is inevitable. On the other hand, if the membrane is not depolarized to threshold, no AP can occur. What is this mechanism called? |
|
Definition
|
|
Term
| True or False: At rest, the membrane potential is approx. -70mV. The K+ conductance or permeability is high and K+ channels are almost fully open, allowing K+ ions to diffuse out of the cell down the existing concentration gradient. At rest, Na+ conductance is low and, thus, the RMP is far from the Na+ equilibrium potential. |
|
Definition
|
|
Term
| An inward current, usually the result of current spread from APs at neighboring sites, causes depolarization of the nerve cell membrane to threshold, which occurs at approximately -60mV. This initial depolarization causes rapid opening of ???, causing increase in ??? |
|
Definition
Activation gates of the Na+ channel (sensitive to voltage)
Na+ conductance promptly increase and becomes even higher than the K+ conductance. |
|
|
Term
| True or False: The increase in Na+ conductance during the upstroke of the action potential, results in an inward Na+ current; the membrane potential is further depolarized toward, but does not quite reach, the Na+ equilibrium potential of +65mV. |
|
Definition
|
|
Term
| Tetrodotoxin (a toxin from the Japanese puffer fish) and the local anesthetic lidocaine block these voltage-sensitive ??? and prevent the occurence of nerve action potentials. |
|
Definition
|
|
Term
| Tetraethylammonium (TEA) blocks voltage dependent ??? |
|
Definition
|
|
Term
| The upstroke is terminated, and the membrane potential repolarizes to the resting level as a result of two events. What are the two events? |
|
Definition
First, the inactivation gates on the Na+ channels respond to depolarization by closing, but their response is slower than the opening of the activation gates. Thus, after a delay, the inactivation gates close the Na+ channels, terminating the upstroke.
Second, depolarization opens K+ channels and increases K+ conductance to a value even higher than occurs at rest.
The combined effect of closing of the Na+ channels and greater opening of the K+ channels makes the K+ conductance much higher than the Na+ conductance. Thus, an outward K+ current results, and the membrane is repolarized. |
|
|
Term
| For a brief period following repolarization, the is higher than at rest, and the membrane potential is driven even closer to the K+ equilibrium. Eventually ??? returns to the resting level, and the membrane potential depolarizes slightly, back to the RMP. |
|
Definition
|
|
Term
| The basic assumption of Na+ channels is that Na+ can only move through the channels when both gates on the channel are open. In regards to depolarization, the activation gate opens quickly, and the inactivation gate closes after a time delay. |
|
Definition
|
|
Term
| At rest, the ??? is closed. Although the inactivation gate is open (because the membrane potential is hyperpolarized, ??? can't move through the channel. |
|
Definition
|
|
Term
| During the ???, depolarization to threshold causes the activation gate to open quickly. The inactivation gate is still open because it responds to ??? more slowly than the activation gate. Thus, both gates are open briefly, and Na+ can flow through the channel into the cell. |
|
Definition
Upstroke of AP
Depolarization |
|
|
Term
| At the peak of the action potential, the ??? finally responds and closes, and the channel itself is closed. Repolarization begins. When the membrane potential has repolarized back to its resting level, the inactivation will be open, both in their original positions. |
|
Definition
|
|
Term
| This overlaps with almost the entire duration of the AP. During this period, no matter how great the stimulus, another AP cannot be elicited. The basis for this is the closure of the inactivation gates of the Na+ channel in response to depolarization. |
|
Definition
| Absolute Refractory Period |
|
|
Term
| Period begins at the end of the absolute refractory period and overlaps primarily with the period of the hyperpolarizing afterpotential. During this period, an AP can be elicited, but only if a greater than usual depolarizing (inward) current is applied. |
|
Definition
| Relative Refractory Period |
|
|
Term
Propagated without decrement
All-or-none response
Voltage inactivation of the action potential
Refractory periods
represent the ??? |
|
Definition
| Properties of Action Potentials |
|
|
Term
Properties of action potentials
•Stereotypical Size & Shape
o Each normal AP for a given cell type looks identical
•Propagated without decrement
o An AP at one site causes depolarization at adjacent sites, bringing those adjacent sites to threshold
o Propagation of AP from 1 site to next is nondecremental
•All-or-none response
o As long as you get threshold, you get an AP
•Voltage inactivation of the action potential
o AP will eventually come back from a positive charge because you are inactivating Na+ channels |
|
Definition
|
|
Term
Mechanism of the voltage-sensitive K+ channel (Has 2 states & only 1 activation gate)
•Resting State
o Activation gate is closed
o Gate is located on the inside
•Slow activation state
o Activation gate opens allowing conductance |
|
Definition
|
|
Term
•Blocks fast Na+ channels, but does NOT block leak channels
o Blocks in [nM] so you will need a higher concentration
o Will not see an Action potential.
o There will be a little bit of hyperpolarization because K+ will efflux. It will remain hyperpolarized until you remove the clamp |
|
Definition
|
|
Term
•Blocks in [mM], does not effect leak channels
o Will SEE an action potential
o The DURATION is prolonged
o There will not be much after-hyper polarization
o Peak will be closer to ENa
o Will finally approach resting potential once Na+ voltage gated channels close because they are time dependent |
|
Definition
|
|
Term
When is the K+ conductance or permeability high and K+ channels are almost fully open, allowing K+ ions to diffuse out of the cell down the existing concentration gradient?
Na+ conductance is highest when? |
|
Definition
|
|
