Term
| What does the ion movement across a membrane do? |
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Definition
| It creates a charge transfer (a current). This is a voltage. |
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Term
| What is the rate of ion transfer by carrier proteins? |
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Definition
| it is pretty small. Because it is limited by how much the carrier protein can change conformations. |
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Term
| How can larger currents be created across membranes? |
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Definition
| By opening channels that allow ions to rush in/out of the cell. |
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Term
| How long does it take for the voltage to change if you open a channel? |
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Definition
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Term
| What type of current usually flows in biological systems (as opposed to electrical ones)? |
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Definition
| In electric systems, you have neurons traveling around. In biological systems, ions usually carry a POSITIVE charge. |
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Term
| What's the fancy definition for current? |
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Definition
| The RATE of charge movement through a medium. |
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Term
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Definition
| Ease with which a charge moves through material. |
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Term
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Definition
| How hard it is for something to move through material (exactly the inverse of conductance) |
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Term
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Definition
| Separation of charges across a resistor. |
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Term
| How can you measure the voltage of a cell? |
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Definition
| Stick a glass voltmeter into it. Then, measure it compared to the extracellular fluid. |
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Term
| What voltage does the inside of the cell have? |
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Definition
| It is NEGATIVE. Usually -70 millivolts to the extracellular fluid. |
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Term
| What is the difference between the voltage outside and inside of the cell called? |
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Definition
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Term
| How is the membrane potential created/maintained? |
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Definition
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Term
| What is the usual concentration of K+ inside a cell? |
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Definition
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Term
| What is the concentration of Na+ outside a cell? |
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Definition
| 145mM (inside the cell is just like 10) |
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Term
| Where is there more chloride? Inside or outside the cell? |
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Definition
| Outside (110mM) to 5mm inside. |
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Term
| where is there more Calcium? |
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Definition
| Outside has 2mM. Inside has like 0.0001mM |
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Term
| Which types of ion channels are in most cells? |
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Definition
| Ones for K, Na, Cl, and Ca |
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Term
| Which type of ion channel contributes the most to the membrane conductance? |
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Definition
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Term
| If you poke a hole in a cell, where will the K+ ions go? what will happen after that? |
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Definition
| Basically, K+ will rush out of the cell, until there is an equilibrium. The equilibrium has to do both with concentration, but also with electrostatic forces inside the cell. Because as the cell becomes more negative (when the K rushes out), it will eventually start attracting K+ back. There is like an equilibrium between opposing forces of electrostatics and concentration. |
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Term
| What would concentration and electrostatic gradients have to be for K+ to stop rushing out of a cell? |
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Definition
| basically, you'd need electrostatics and concentration gradients to be equal. The concentration gradient would be pulling out, and the electrostatic gradient would be equal, and then the K+ ions would stop flowing. |
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Term
| What is the equilibrium potential? |
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Definition
| The value of Vm where the concentration gradient and the electrostatic force are balanced is called the equilibrium potential or the reversal potential (Veq, or Vrev). The reversal potential for K+ is called VK, for Na+ it is VNa, and so on. |
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Term
| what does Vm stand for? and what is happening when the Vm is stable? |
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Definition
| This is about membrane potential. When it is stable, you have no movement of ions across the membrane (or there is balanced movement, so the net charge is zero). |
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Term
| If positively charged ions move into the cell, what happens to the Vm? what is this called? |
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Definition
| it gets less negative. This is called depolarization. |
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Term
| If anions move out of the cell, what happens to the Vm? what is this called? |
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Definition
| If anions move out, the Vm also becomes less negative. This is also depolarization. |
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Term
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Definition
| When the cell's membrane potential (Vm) becomes less negative. |
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Term
| What happens if cations exit? Or anions enter? what's this called? |
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Definition
| This is called hyperpolarization. it is when the cell Vm becomes more negative. |
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Term
| How can we calculate the Veq and what does this mean? |
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Definition
| Nernst equation. Veq is the membrane potential at equilibrium. |
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Term
| What is the nernst equation? At t=20'C |
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Definition
| Veq(S) =58/zs • log([S]o/[S]i) |
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Term
| What is the movement of cations out of a cell called? what does it do? |
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Definition
| this is called outward current. it hyperpolarizes the cell. |
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Term
| What is the movement of cations out of a cell called? what does it do? |
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Definition
| this is called outward current. it hyperpolarizes the cell. |
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Term
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Definition
| the rate of charge transfer from one point to another |
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Term
| What units express current? |
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Definition
| amperes. picoamperes (10^-12 amperes), nanoamperes (10^-9 amperes) |
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Term
| What does a large current signify? |
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Definition
| a lot of ions are moving across the cell membrane per unit time |
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Term
| What is "driving force?" What does it mean? |
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Definition
| Driving force = Vm - Veq. This is the electrochemical force that will make an ion move into/out of the cell. If the driving force is positive, stuff will rush out of the cell. |
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Term
| Besides driving force, what's another factor that will determine the size of a current carried by a given ion species. |
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Definition
| How easily it can pass through the membrane. This is similar to the idea of conductance/resistance. Biological membranes are strong resistors. |
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Term
| What units are conductance measured in? |
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Definition
| siemens (or picosiemens 10^-12) |
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Term
| What units are resistance measured in? |
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Definition
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Term
| what is Ohm's law? What does it mean? |
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Definition
| Ohm’s law describes the simple relationship between current, voltage, and conductance. |
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Term
| What is the Ohm's law equation? Describe it. |
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Definition
| I = g x v. This means that current = conductance x voltage. This means membrane current for specific ion species = the conductance of the membrane for that ion x the driving force of that ion. |
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Term
| How would you graph ohm's law? |
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Definition
| It would be like a linear curve. the slope would be conductance. Current (I) would be on the Y axis. Vm-Veq (driving force) would be on the X axis. |
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Term
| When the cell is at Veq, what would the driving force be? |
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Definition
| Driving force would be zero, because Vm would be equal to Veq! On a graph of Ohm;s law, this would be at the origin. |
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Term
| What is Ohm's law with resistance used instead of conductance? |
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Definition
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Term
| How does conductance mathematically relate to the driving force? |
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Definition
| Conductance is inversely proportional to voltage. So the higher the conductance, the lower the voltage. |
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Term
| How does resistance relate to voltage changes? |
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Definition
| The more resistance a cell has in its membrane, the more change in Vm is seen with application of current. |
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Term
| What does capacitance mean? |
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Definition
| Real cell membranes are able to conserve their electrical charge. Also, if you add a current to a membrane, the actual Vm might not change much, because the membrane will absorb the charge until saturated--only upon saturation of charge in the membrane will you see a voltage change. |
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