Term
| Describe the typical intracellular neurone concentrations |
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Definition
| In a typical neurone intracellular K+ concentration is high (~100-150mM) while Na+ and Cl- are low (~5-10mM); extracellular concentrations of these ions are inverted. |
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Term
| Describe a typical neurones resting membrane potential |
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Definition
| In a typical neurone the resting membrane potential is set in the range of -60 to -70mV, mainly due to the background activity of K+ channels and the work of Na+/K+ ATPase; most other ion channels are closed at rest. |
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Term
| Give the Ek value and the consequence of K+ channel activation |
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Definition
| EK ~ -90 mv : activation of K+ channels hyperpolarizes the membrane and increases voltage needed to reach the AP firing threshold (inhibition) |
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Term
| Give the ENa value and the consequence of Na+ channel activation |
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Definition
| ENa ~ +65 mv : activation of Na+ channels depolarizes the membrane (excitation) |
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Term
| Give the ECa value and the consequence of Ca2+ channel activation |
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Definition
| ECa ~ +110 mv : activation of Ca2+ channels depolarizes the membrane (excitation) |
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Term
| Give the Ecat value and the consequence of non-selective cation channels channel activation |
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Definition
| Ecat ~ 0 mv : activation of non-selective cation channels (these cannot discriminate between small cations) depolarizes the membrane (excitation) |
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Term
| Give the ECl value and the consequence of Cl- channel activation |
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Definition
| ECl varies dramatically but in most CNS neurons is ~ -90 mv; activation of Cl- channels in these neurons is inhibitory |
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Term
| How is driving force calculated? |
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Definition
| Driving force = (Vm – Eion) |
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Term
| If the membrane potential is -10 mV, is the driving force for K+ ions positive (outward) or negative (inward)? |
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Definition
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Term
| If the membrane potential is -100 mV, is the driving force for K+ ions positive (outward) or negative (inward)? |
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Definition
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Term
| If the membrane potential is 30 mV, is the driving force for Na+ ions positive (outward) or negative (inward)? |
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Definition
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Term
| If the membrane potential is -70 mV, is the driving force for Na+ ions positive (outward) or negative (inward)? |
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Definition
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Term
| If the membrane potential is 0 mV, is the driving force for Cl- ions positive (outward) or negative (inward)? |
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Definition
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Term
| If the membrane potential is -100 mV, is the driving force for Cl- ions positive (outward) or negative (inward)? |
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Definition
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Term
| Define reversal potential |
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Definition
| the membrane potential at which the direction of current flow reverses |
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Term
| What does a voltage clamp measure? |
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Definition
- voltage is controlled and the current across the membrane is recorded
- allows direct testing of active ion channels properties
- it allows the experimenter to adjust the potential difference applied across the membrane and measure the resulting current flowing. |
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Term
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Definition
| Voltage, also called electromotive force, is the potential difference in charge between two points in an electrical field. In other words, voltage is the "energy per unit charge”. |
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Term
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Definition
| Current is the rate at which electric charge flows past a point in a circuit. In other words, current is the rate of flow of electric charge. |
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Term
| What does a current clamp measure? |
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Definition
- current is controlled and voltage responses are recorded
- can mimic APs and synaptic input |
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Term
| Describe the role of sodium channels in the AP |
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Definition
1) voltage-gated sodium channels open upon depolarisation, causing an influx of Na+ ions into the cell
2) influx further depolarises membrane, causing more Na+ channels to open
3) influx of sodium drives the membrane potential (Vm) towards (and above) 0mV (towards ENa)
4) explosive influx of Na+ ions only occurs if the membrane potential exceeds the threshold potential (>-55mV) at which voltage-gated Na+ channels start to activate
5) Na+ channels inactivate rapidly. No AP is possible until the refractory period is over. |
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Term
| Describe the role of potassium channels in the AP |
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Definition
1) voltage-gated K+ channels open in response to depolarisation but at more positive potentials than Na+ channels
2) Most Kv channels are closed at rest, however, some (plus some non-voltaged-gated K channels - leak channels) remain open to maintain resting membrane potential near the Ek
3) the delayed opening of the Kv channels is a main factor responsible for the depolarising phase of the AP |
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Term
| What relation do Ca2+-activated K+ channels have to the AP |
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Definition
- can contribute to AP depolarisation
- respond to activation of voltage-gated calcium channels that contribute to depolarisation in a similar way as Na+ channels do |
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Term
| Describe the events that lead up to Ca2+-activated K+ channels |
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Definition
1) Depolarisation
2) Ca2+ channels open
3) Ca2+ influx
4) Ca2+-activated K+ channels open
5) K+ efflux
6) Depolarisation |
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Term
| How long do Ca2+-activated K+ channels remain open for? |
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Definition
| Calcium activated potassium channels often remain open longer than voltage gated potassium channels, and therefore can prolong the undershoot observed after the action potential (afterhyperpolarisation). |
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Term
| Where in the CNS are APs usually generated? |
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Definition
| axon initial segment (AIS) |
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Term
| Where are voltage gated ion channels concentrated at? |
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Definition
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Term
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Definition
1) initial depolarization reaching firing threshold;
2) Voltage gated Na+ channel opening causes massive depolarization;
3) Voltage gated K+ channels start to open and to repolarize the membrane potential;
4) Na+ channels inactivate; membrane potential repolarizes with an overshoot;
5) Voltage gated K+ channels deactivate; membrane potential returns to the resting value |
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