Term
| difference in the kinetics of VG sodium & VG potassium channels |
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Definition
VG sodium channels are quickly activated & then slowly inactivated
VG potassium channels are slowly activated & then deactivated |
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Term
| difference in how fast sodium activation vs inactivation gates move |
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Definition
| activation gates of sodium channels move faster than their inactivation gates |
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Term
| Is there an important time component when dealing with VG sodium channel m-gates & h-gates? |
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Definition
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Term
| Are sodium activation & inactivation separate processes? |
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Definition
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Term
| What is the difference between how intracellular pronase affects sodium inactivation vs activation? |
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Definition
| removes inactivation, but does not alter activation |
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Term
| 2 gates where "open" means the channel is open |
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Definition
1. sodium "m" gate
2. potassium "n" gate |
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Term
| gate where "open" is when the cell is at rest |
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Definition
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Term
| How do the voltage levels that make m & n gates likely to open affect h gates? |
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Definition
| they are the same voltage levels that make h gates likely to be closed |
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Term
| For a gate, does a lower time constant indicate faster or slower movement? |
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Definition
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Term
| Does the sodium m gate have a really fast or really slow time constant compared to sodium h or potassium n gates? |
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Definition
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Term
| 3 ways time constants can be regulated |
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Definition
1. phosphorylation
2. different drugs
3. binding of auxiliary subunits |
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Term
| Macroscopic currents (smooth graph) are the sum of the individual ______ |
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Definition
| single channel currents (microscopic currents) |
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Term
| What does a sodium channel opening look like on a single channel current record? |
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Definition
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Term
| What does a sodium channel closed look like on a single channel current record? |
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Definition
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Term
| Why do you only see one opening on sodium single channel recordings? |
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Definition
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Term
| Chunky rectangular currents sum together to make ______ |
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Definition
| smooth whole cell current that we see on the overall graph |
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Term
| Is channel activity random? |
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Definition
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Term
| How can you try to predict macroscopic current? |
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Definition
| you can do individual single channels over & over |
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Term
| Is the current when a single channel is open through that channel dealing with probability? |
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Definition
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Term
| Does whole cell current look linear? |
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Definition
| no! (THINK: IV plots you're used to seeing) |
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Term
| How do voltage-gated channels sense membrane voltage? |
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Definition
| voltage field across membrane |
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Term
| Where is the voltage sensor located? |
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Definition
| the S4 region of the channel! |
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Term
| The macroscopic current is simply the sum of the _____ |
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Definition
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Term
| Remember: when you are working with single channel current, what conductance must you use? |
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Definition
| single channel conductance (gamma) |
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Term
| On an IV plot, what does the single channel current look like? |
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Definition
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Term
| The summed sodium current measured during an action potential is the sum of _______ |
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Definition
| all the microscopic currents |
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Term
| difference in appearance between single channel current & whole cell current |
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Definition
| single currents look like blocky chunks, whole cell looks nice & smooth |
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Term
| During a single AP, [Na] & [K] changes are tiny - why? |
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Definition
| small amount of matter, huge amount of charge; amount of ions that flow across the membrane to cause the membrane potential to change during an AP is actually pretty small |
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Term
| What is the role of the ATPase pump long-term versus during a single AP? |
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Definition
| important for long-term...it isn't necessary to deal with just one action potential or even just a few action potentials; a single AP doesn't deplete the concentration gradients |
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Term
| How does the size of concentration change depend on the axon diameter? |
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Definition
| bigger the axon, smaller the [Na] & [K] change during an AP |
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Term
| Why is a squid AP propagation ~20 m/s but in vertebrates up to ~100 m/s? |
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Definition
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Term
| What does it mean that dendrites = passive cable? |
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Definition
| passive = not activating voltage-gated channels |
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Term
| Is the soma an active or passive "sphere"? |
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Definition
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Term
| Is the axon an active or passive cable? |
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Definition
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Term
| 2 directions of current flow in a fiber |
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Definition
1. out of the fiber (bad) through membrane resistance
2. along the fiber (good) through the longitudinal resistance |
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Term
| Does a longer fiber have more or less membrane resistance? |
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Definition
| less! (THINK: adding resistors in parallel, they get added in reciprocals) |
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Term
| Does a longer fiber have more or less longitudinal resistance? |
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Definition
| more! (THINK: adding resistors in series, you just add them straight up) |
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Term
| Why do electrotonic potentials tend to decrease with distance from stimulation site? |
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Definition
| because of current flow out of the fiber through the membrane resistance |
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Term
| There is an ______ relationship between the membrane potential & distance along axon from current injection |
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Definition
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Term
| Is the length constant (lambda) of the fiber kind of like how tau is the time constant? |
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Definition
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Term
| Is good propagation (fast propagation of ions) associated with a long or short length constant? |
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Definition
| good propagation (fast propagation of ions) = long length constant |
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Term
| What does the length constant (lambda) of a fiber tell you? |
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Definition
| how far down the axon the current is going to go |
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Term
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Definition
| distance at which the membrane potential decays to 37% of the maximum voltage at distance = 0 |
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Term
| The length constant will have a ______ type of unit |
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Definition
| length (ex. mm, cm, m, etc.) |
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Term
| Why does the length constant (lambda) increase when membrane resistance increases? |
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Definition
| makes it harder for current to leave the fiber |
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Term
| Why does length constant (lambda) decrease when longitudinal resistance increases? |
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Definition
| makes it harder for current to travel down the fiber |
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Term
| Why does membrane resistance decrease when radius of the fiber increases? |
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Definition
| more surface area for channels (proportional to 1/d) |
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Term
| Does longitudinal resistance or membrane resistance decrease more when the radius of the fiber increases? |
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Definition
| longitudinal resistance (making it easier for current to flow down the fiber) |
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Term
| overall: increasing neuron diameter ______ the length constant |
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Definition
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Term
| Why is the change in membrane potential slower farther away? |
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Definition
| the farther you go down the axon, the more membrane has to be charged, which means the more capacitance has to be charged |
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Term
| Basically, you have more capacitance so the AP will move more ______ |
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Definition
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Term
| How does diameter change the speed of membrane charging? |
|
Definition
| the larger the diameter, the more surface area --> the more surface area, the more capacitance --> the more capacitance, the longer it takes to charge |
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Term
| Do dendrites act like passive fibers? |
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Definition
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