Term
| How does diameter change the speed of membrane charging? |
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Definition
| increasing the diameter increases the area so membrane potential change will be slower because there is more membrane to charge |
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Term
| What assumption must be made to think that dendrites act like passive fibers? |
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Definition
| there are not voltage gated ion channels |
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Term
| From where do dendrites receive input? |
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Definition
| synapses with axons of other neurons |
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Term
| Do excitatory postsynaptic currents (EPSCs) cause big or small changes in the potentials of the dendritic membrane (EPSP)? |
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Definition
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Term
| The EPSCs in the dendrites must make it all the way to the ______ to be integrated |
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Definition
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Term
| Why is there a smaller EPSP recorded at the soma versus the dendrite? |
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Definition
| lost current along the way |
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Term
| Is the EPSP in the soma smaller & slower or bigger & faster than EPSP out on dendrite? |
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Definition
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Term
| dendrite --> active or passive? |
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Definition
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Term
| 2 steps in the regeneration of an action potential from "point A" to "point B" in active channels |
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Definition
1. depolarization at "point A" opens voltage-gated sodium channels & the regenerative current gives rise to an action potential
2. the spread of the positive current from "point A" brings the next segment ("point B") to threshold for regenerative sodium current |
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Term
| 2 steps in active channels preventing current loss |
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Definition
1. current loss is prevented because each region is passively depolarized by the action potential generated in the preceding region
2. as long as threshold for the regenerative sodium current is met, the action potential is renewed in the next segment - prevents decrement |
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Term
| Where action potential has already been, that part of the membrane is ______ |
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Definition
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Term
| Part of the membrane that is maximally depolarized is where ______ |
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Definition
| sodium is entering --> passively diffusing ahead to bring the next part of the axon to threshold (just starting to be depolarized, just approaching threshold) |
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Term
| 2 places where myelin (what wraps large nerve fibers) is formed |
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Definition
1. Schwann cells (PNS)
2. oligodendrocytes (CNS) |
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Term
| The myelin acts as an insulator & greatly increases or decreases effective membrane resistance? |
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Definition
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Term
| What is the relationship between number of wrappings (10 - 160) & resistance to current flow? |
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Definition
| the greater the number of wrappings, the greater the resistance to current flow |
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Term
| What are the spaces between myelinated areas? |
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Definition
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Term
| What is effect of myelin on capacitance of axon? |
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Definition
| decreasing capacitance because there is a greater distance between the charges stored on the outside of the myelin & the charges passing through the inside of the membrane |
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Term
| What is effect of myelin on membrane resistance? |
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Definition
| when you add myelin, you're increasing membrane resistance |
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Term
| What is effect of myelin on longitudinal resistance? |
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Definition
|
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Term
| What is effect of myelin on length constant? |
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Definition
| length constant is much bigger! |
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Term
| Nodes between axon myelination occur about every _____ mm |
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Definition
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Term
| Axon myelination causes separation that is about _____x the diameter of the axon |
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Definition
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Term
| The width of a node between axon myelination is about ______ microns |
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Definition
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Term
| Schwann cells wrap ______ times around the axon! |
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Definition
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Term
| Where are voltage gated channels restricted to in myelinated axons? |
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Definition
| breaks in the myelin called Nodes of Ranvier |
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Term
| Where are sodium channels concentrated in myelinated axons? |
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Definition
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Term
| Where are potassium channels concentrated in myelinated axons |
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Definition
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Term
| Myelin restricts current flow to the ______ where current flows easily through the channels |
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Definition
|
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Term
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Definition
| due to high resistance internodal regions, current jumps (saltare) from node to node |
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Term
| Is myelination much more or much less efficient? |
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Definition
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Term
| The diameters of myelinated axon can be _____x smaller than an unmyelinated axon & have the same effects |
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Definition
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Term
| Velocity along a myelinated axon is _____x faster than an unmyelinated axon |
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Definition
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Term
| Do you need more or fewer sodium/potassium ATPases in a myelinated axon? |
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Definition
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Term
| Why does adding myelin to an axon decrease that section of the axon's capacitance? |
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Definition
| think of outside of myelin & the internal axon membrane as the two plates...they are now very far apart! |
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Term
| many myelin lipid layers --> more or less membrane resistance? |
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Definition
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Term
| thinking in terms of distance (AP propagating from left to right): area ahead of the action potential = ? |
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Definition
|
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Term
| outward capacitive current = hyperpolarizing or depolarizing? |
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Definition
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Term
| Is sodium current passively hyperpolarizing or depolarizing the segment of axon ahead of it? |
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Definition
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Term
| Why does the sodium current have a weird bump at the peak of the action potential? |
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Definition
| the peak is where there's a puny sodium driving force; as the cell is repolarizing, there is a little bit more influx of sodium & then it just goes back up normally |
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Term
| Is there a steady inward or outward capacitive current behind action potential? |
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Definition
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Term
| What happens at the unmyelinated parts of an axon? |
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Definition
| membrane potential changes/current is flowing |
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Term
| When you are thinking in terms of distance, the AP is propagating from ______ to ______ |
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Definition
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Term
| In a myelinated axon, sodium current is confined to ______ |
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Definition
| Nodes of Ranvier (the unmyelinated parts of the axon) |
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Term
| In a myelinated axon, capacitive currents are located just at the ______ |
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Definition
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Term
| What is the key factor of AP propagation in a myelinated axon? |
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Definition
| bring the next Node of Ranvier to threshold |
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Term
| In a myelinated axon, behind AP, do you have inward or outward capacitive current? |
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Definition
| inward (hyperpolarizing the nodes behind it) |
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