Active processes requiring energy to maintain electrical gradients.
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What is electrotonic conduction?
The passive spread of electrical signals.
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Why does current flow?
Current flows between two points if there is a potential difference between them and they are connected by a conductor.
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What ions travel from the outisde of the cell inwards?
Sodium, chloride and calcium.
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What ions travel from the inside of the cell outwards?
Potassium.
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What does the membrane resistance of the lipid bilayer depend on?
The density of open ion channels.
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What is capacitance?
The store of charge that builds up on the membrane for a given voltage.
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Describe a capacitor in terms of a cell.
A capacitor consists of two conductors separated by a thin insulator. In the cell the intra and extracellular fluid act as the conductors and the lipid bilayer as the insulator.
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What is capacitance proportional to?
surface area/insulator thickness
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Describe the equivalent circuit of a patch of cell membrane.
Membrane capacitance (Cm) and membrane resistance (Rm) are in parallel with each other.
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What is the time constant, tau?
A way of describing the exponential time course of a change in membrane potential. It is the time at which the membrane voltage has reduced to 63% of Vmax.
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What is the formula for the time constant?
Vmax x (1-e^(-t/RC))
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What is the time constant proportional to?
Rm x Cm
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What type of cells does Vm rise slowest in?
Large cells and cells with high membrane resistances.
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When does Vm increase linearly with current?
For subthreshold stimuli.
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What factors make it more likely a current will trigger an AP?
Making the stimulus longer and a larger current.
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What does cable theory state?
In long cellular processes passive responses decay with distance from the stimulus.
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What is the length constant, lambda?
The distance from the current injection point when the voltage signal has decreased to 37% of its original value.
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What is the equation for lambda?
Vm = Vmax x e^(-x/lambda)
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How do APs travel in excitable cells?
They are constantly regenerated by ion channels as they propagate.
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What are the three components of resistance?
Rm, Ra and Rext.
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How can you increase conduction?
Insulate the membrane (Schwann cells) and increase the amount of cytoplasm (thus increasing cell diameter)
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When is the length constant greatest in physiological conditions?
When Rm is high and when Ra is low.
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Other cards in this set
Card 2
Front
What is electrotonic conduction?
Back
The passive spread of electrical signals.
Card 3
Front
Why does current flow?
Back
Card 4
Front
What ions travel from the outisde of the cell inwards?
Back
Card 5
Front
What ions travel from the inside of the cell outwards?
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