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15 Cards in this Set
- Front
- Back
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Why do excitable cells need to use potential energy? |
To do work: muscle contract, immune cells move, nerve cells signal - info.carried over a relatively long distance |
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What is action potential?
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The different in ion concentration across nerve cell membrane to provide potential energy required for transmitting nerve impulses |
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Plasma membrane potential (Vm) |
the separation of electrical charges across the cell membrane
Vm varies with cell types Some: static-homeostasis and substrate transport Some: changes- signal transduction, action potential |
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Na/K ATPase, why is there a charge separation? |
Due to action of Na pump |
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Na/K ATPase, what generates AP? |
Na out, K in The number of ions x related |
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Na/K ATPase: Mechanism of action |
1. Binding of cytoplasmic Na -> protein stimulates phosphorylation by ATP 2. Phosphorylation -> change conformation of the protein 3. Conformational change expels Na out and extracellular K binds 4. K binds triggers the release of phosphate group 5. Loss of phosphate -> restore original conformation 6. K released inside, Na site repeats, cycle repeats |
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Ions distribution for an excitable cell |
Na: in < out > K: in > out < Cl: follow K Ca: in >, out < A-: in > out < |
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Effect of K on Vm of skeletal muscle |
Linear relationship/ Logarithm relationship Increase extracellular K depolarises the cells Nerstian |
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Resting potential |
Due to increase permeability of K Electrical neutrality: High K inside , high Na outside K leak out through a leak channel, K goes down concentration gradient, -ve charge protein line up on the other side of the membrane, try to attract the K in => separation of charge => membrane potential |
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What does balance the Na outside the cell? |
Cl |
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What does balance K inside the cell? |
-ve charge protein |
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Electrochemical equilibrium |
Concentration tends to drive K out of the cell but A- attracts K back in => electrical potential balances the chemical potential => equilibrium established |
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Equilibrium potential |
Voltage at which the electrical force experienced by an ion is equal and opposite to the chemical force produced by the concentration gradient.
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Nernst equation |
The voltage across the membrane is proportional to the ratio of the ion concentration on either side of the membrane
Assuming that the membrane is permeable to those ions |
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Goldman equation |
give more realistic approximation of membrane potential
As long as the concentration of the ions does not change, Vm is controlled by the permeability due to the opening, closing of protein ion channels in the membrane |
