Neuroscience basics

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  • Created by: Jess
  • Created on: 14-05-14 11:50
Why do AP shapes vary in different cells?
Differences in ion channel populations and properties.
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Why is there an upper limit to neuron firing frequency?
Due to refractory periods.
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What is refractoriness?
The reduction in membrane excitability following an action potential.
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What is the absolute refractory period?
The period during which a neuron cannot fire a second action potential no matter how big the stimulus.
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What governs AP conducton velocity?
Passive electrical properties of the membrane.
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How do factors that increase the length constant (low Ra, high Rm) affect current flow?
They enhance AP conduction velocity by icreasing longitudinal flow of current.
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How do factors that shorten the time constant (low Cm, low Rm) affect current flow?
Enhance rate of depolarisation (speed of upstroke) which increases electrical gradients between active and resting zones speeding up AP propagation.
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What is the evidence for local circuit theory?
Small voltage transients still recorded when AP is blocked by nerve cooling, changing Ra amd Rext alters conducton velocity, conduction velocity is greater in large than small diameter axons.
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What does a myelin sheath do?
Increases Rm and decreases Cm by increasing length constantsand decreasing time constants making electrotonic conduction faster.
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What is a Node of Ranvier?
Gaps in the myelin sheath where ion channels are located. AP is actively boosted and regenerated at the nodes and travels passively between them.
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What is the evidence that current flow occurs only at the Nodes of Ranvier?
Threshold stimuli is lower if applied at nodes rather than internodes, application of anaesthetics blocks more effectively at nodes, no current in ringer solution if the pool does not contain a node.
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Below what diameter are unmyelinated axons faster at conducting?
1 micrometer.
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What is velocity proportional to in unmyelinated axons?
Square root of the diameter. So need large changes in diameter to produce modest changes in velocity.
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Card 2

Front

Why is there an upper limit to neuron firing frequency?

Back

Due to refractory periods.

Card 3

Front

What is refractoriness?

Back

Preview of the front of card 3

Card 4

Front

What is the absolute refractory period?

Back

Preview of the front of card 4

Card 5

Front

What governs AP conducton velocity?

Back

Preview of the front of card 5
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