Term
| What creates electrical potential? |
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Definition
1) Ion-specific concentration gradients
2) Ion-specific membrane permeability |
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Term
| Distribution of major ions |
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Definition
Na: 145 mM out, 15 mM in
K: 5 mM out, 100 mM in
Cl: 100 mM out, 7 mM in |
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Term
| Important membrane potential values |
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Definition
Resting potential: -65 mV
Threshold: -40 mV
Overshoot: about +40 mV
E(Na) = +60 mV
E(K) = -90 mV |
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Term
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Definition
Solves for Equilibrium potential
E = (61/Z) log([out]/[in])
Z = ion charge (+1 for K, +2 for Ca)
- When [out]>[in] and Z is positive, electrical potential is positive. (log is positive)
- When [out]<[in] and Z is positive, electrical potential is negative (log is negative) |
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Term
| Electrochemical equilibrium |
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Definition
| When concentration gradient balances with electrical charge gradient |
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Term
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Definition
Predicts resting membrane potential. (Nernst expanded to multiple ions)
Vm = 61 log( (TOP: [K out], [Na out], [Cl in]) /
(BOTTOM: [K in], [Na in], [Cl out]))
- Some channels aren’t selective, so K flows in with Na. If this channel is open, potential moves towards Na equilibrium potential because concentration of Na and K inside and outside will balance, so potential will move towards 0 (less negative). |
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Term
| Summary of steps establishing resting membrane potential |
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Definition
1) Na/K ATPase establishes concentration gradients.
2) Cell membrane more permeable to K than Na
3) Steady state: Na and K flux balanced by Na/K ATPase pump |
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Term
| Osmolarity in Renal Medulla of Kidney |
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Definition
| High osmolarity in renal medulla of kidney for production of concentrated urine |
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Term
| What causes localized depolarizing graded potentials? |
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Definition
| Localized opening of ligand-gated Na channels. Electrical conduction causes depolarization. Current decreases as distance from Na channel increases because of resistance and current leakage through other ion channels. |
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Term
| Why does hyperpolarization go lower than resting membrane potential? |
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Definition
| K permeability is higher than normal while Na permeability already normal |
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Term
| Voltage dependencies of Na and K channels and what kind of feedback |
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Definition
Na channels are closed at resting, open (activated) then close (inactivated) during depolarization. (POSITIVE FEEDBACK)
K channels remain open during depolarization. (NEGATIVE FEEDBACK) |
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Term
| Mechanism of action potential in cardiac cells |
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Definition
Pacemaker: Spontaneous depolarization through Na and Ca influx through funny channels.
Action potential: Rising phase (upstroke) caused by activation of fast Na channels. Plateau phase of depolarization caused by activation of Ca channels and inactivation of K channels. Repolarization caused by opening of voltage-sensitive K channels.
Action potential lasts much longer in cardiac cells than neurons. |
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Term
| Mechanism of neurotransmitter release |
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Definition
1) action potential reaches axon terminal
2) voltage-gated Ca channels open and Ca enters
3) Ca activates SNARE complex and NT release into synaptic cleft
4) NT binds to post-synaptic membrane |
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Term
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Definition
| Sensory, interneuron, motor |
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