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Review Sheet 2-Final (second sheet for new material for the final) BIOL 319
Terms in this set (46)
What is a resting membrane potential?
electric charge difference inside a plasma membrane.
How is resting membrane potential measured?
Measured with a voltmeter just outside the plasma membrane
Explain how resting membrane potentials are standardized to a negative number.
A reference electrode is attached to the outside of the cell, then the machine is adjusted so that it reads zero. A measurement electrode is pierced into the cell, then it compares the value to the reference electrode. This is because voltage has no absolute value, so it is measured by comparing values.
Do all cells have a resting membrane potential?
All cells have a resting membrane potential
What is its significance in an excitable cell?
Excitable cells use their resting membrane potential to create an action potential
What organism and cell type was initially used to measure a resting membrane and why?
The axon of a Loligo squid was first used to measure a resting membrane potential because they have giant axons
What 3 transmembrane proteins establish a resting membrane potential?
Potassium leakage channel (more importance), sodium leakage channel, and sodium-potassium pump
What is the role of the sodium potassium pump in establishing and maintaining the resting membrane potential?
Higher K+ inside the cell than outside, and higher Na+ outside the cell than inside
Pump loads 3 Na+ into the sodium binding sites and pushes them out of the cell
Then, the other side of the pump binds 2 K+ and pushes them into the cell
3 Na+ out, 2 K+ in: outside of the cell becomes more positive so the pump is not enough to balance the charge difference
The pump requires energy (ATP) to complete 1 cycle
What two very important ion gradients does the sodium potassium pump maintain?
The sodium-potassium pump maintains the sodium gradient and the potassium gradient
For K+, what is the direction of the gradient and how does this relate to the difference of concentrations on either side of the membrane?
There's higher K+ outside the cell, so pump pushes K+ against its concentration gradient into the cell
For Na+ what is the direction of the gradient and how does this relate to the difference of concentrations on either side of the membrane?
There's higher Na+ inside the cell, so pump pushes Na+ against its concentration gradient out of the cell
What is an "electrogenic pump"?
Electrogenic pump: generates an electrical character (a voltage or potential across the membrane)
name a relevant example of an electrogenic pump and explain why it is called electrogenic?
Ex: sodium-potassium pump
generates a charge differential across the membrane (bc 3 Na out, 2 K in) which results in a voltage: indirect contribution
creates a gradient of potassium that creates an equilibrium potential for potassium to leak out (-90mV): direct contribution
For every pump cycle of a sodium/potassium pump, how many sodium and potassium are pumped and in which direction are these ions pumped?
1 sodium-potassium pump cycle= 3 Na+ out of the cell and 2 K+ into the cell
For every pump cycle, what does the pump use for energy and how and how much of it does it use?
1 pump cycle requires 1 ATP for energy
Understand the role of the potassium leak channels play in establishing the resting membrane potential.
more important than sodium leak channels
2 K+ in, 2 K+ out
Passes K+ against its concentration gradient out of the cell
Bc there is higher K+ inside the cell
At the same time, other potassium channels push K+ inside the cell bc of the electrical gradient (the loss of K+ inside the cell causes it to be more negatively charged)
Create an equilibrium potential (the electrical gradient that cancels out the chemical/concentration gradient) of -90mV
Understand the role of the sodium leak channels play in establishing the resting membrane potential.
Passes Na+ against its concentration gradient inside the cell
Bc there is higher Na+ outside the cell
Create an equilibrium potential of -85 mV
The overall resting membrane potential is an average of the potassium & sodium equilibrium potentials with potassium having a greater effect since there's way more potassium channels ((-90+65)/2=-85 mV)
What does Pr - stand for?
Pr - are negatively charged molecules (mostly proteins) inside the cell
what is Pr- relationship to potassium ion movement?
Draw more K+ inside the cell after having just left
What two gradients can affect ion flow of an ion across a membrane?
concentration gradient and electrical gradient
Is there a difference between the term "concentration gradient" and "chemical gradient"?
Concentration gradient=chemical gradient (same thing)
is there an equation that equates the chemical gradient with the electrical gradient that will be established to exactly counterbalance the electrical gradient? What is the name of this equation?
Nernst equation: if have different concentrations of an ion on each side of the cell, can use an equation to calculate the electrical potential needed for the ion to exactly counteract that concentration gradient
what is the Equilibrium potential for potassium?
-90mV; when the electrical gradient exactly counterbalances the chemical/concentration gradient of K+ moving from inside to outside of the cell
what is the Equilibrium potential for sodium?
+65mV; when the electrical gradient exactly counterbalances the chemical/concentration gradient of Na+ moving from outside to inside of the cell
What is the term used to specify the membrane potential that exactly counterbalances the chemical gradient so that the two gradients are in "equilibrium" with one another?
What is the explanation for why the overall resting membrane potential is not an equally weighted average between the EK+ of potassium and the ENa+ for sodium?
There are a lot more potassium leak channels than sodium leak channels, so the potassium leak channels have a greater effect on the overall potential
Know how the following parts of the synapse or synaptic events interact during the activation and deactivation of a synapse and the order of this interaction. .Action potential down a neuron, Voltage gated calcium channel, acetylcholine, synaptic cleft, motor end-plate, acetylcholine gated sodium channel, acetylcholinesterase, acetylcholine diffusion.
Why is the presence and activity of acetylcholinesterase every bit as important as acetylcholine release in the first place?
Acetylcholinesterase prevents acetylcholine from keeping channels open longer than they should, and allows the body to control over muscle contraction.
Uncontrolled muscle contractions cause convulsions (bad).
Uncontrolled acetylcholine: motor end plate would continuously be depolarized and create continuous action potentials down the muscle cell
What affect might you expect a powerful acetylcholinesterase inhibitor to have on neuromuscular physiology?
Acetylcholinesterase inhibitors inhibit acetylcholinesterase (an inhibitor), so it stimulates the production of acetylcholine. Potent acetylcholinesterase inhibitors can cause death since they cause the body to go into uncontrollable full body contractions and the person would not be able to breathe and would uncontrollably defecate, vomit, and choke on their own saliva.
What is sarin?
nerve gas that is an acetylcholinesterase inhibitor and causes uncontrollable full body contractions; chemical weapon
Why is sarin so terrible?
End up not being able to breathe, and uncontrollably defecating, vomiting, and choking on your own saliva
are all acetylcholinesterase inhibitors equally potent? Are they all used as "illegal weapons of war"?
no they aren't all equally as potent & no they aren't all illegal weapons of war
How might acetylcholinesterase inhibitors that are less potent be used in general?
Mild acetylcholinesterase inhibitors can be used to treat diseases where the body doesn't make enough acetylcholine
The acetylcholinesterase inhibitor (inhibitor of an inhibitor) stimulates acetylcholine production
Can also be used as insecticides: insects can't breathe so they die; not toxic to humans/dogs
What effect does depolarization have on the sarcolemma that borders the motor end plate?
Depolarization activates the voltage-gated sodium channels and the voltage-gated potassium channels on the sarcolemma that borders the motor end plate, which then create an action potential that self-propagates down the entire length of the muscle cell
How is the activation of the voltage (v) -gated sodium channels and v-gated potassium channels function like "a cascade of falling dominoes'?
It is a self-propagating chain reaction: an AP depolarizes an area of the plasma membrane, which causes the V-gated sodium channels next to that AP to open & depolarize, which then causes the V-gated channels next to that AP to open & depolarize...
Specifically, what role do the v-gated sodium channels play in orchestrating the action potential (AP)?
V-gated sodium channels open first (bc they're more sensitive)
They let Na+ into the cell, causing a depolarization (membrane potential becomes more positive)
This causes the front half of the wave
Specifically, what role does the v-gated potassium channels play in producing the action potential (AP)?
Open immediately after the V-gated sodium channels close
They move K+ out of the cell, causing repolarization (return of membrane potential to its resting value)
This causes the back half of the wave
Does the AP "move"?
An AP does NOT "move." An AP causes an area of the plasma membrane next to it to create another AP, which then causes an area of the plasma membrane next to it to create another AP.....
How is it a "rolling wave of depolarization/repolarization"?
It is a self-propagating chain reaction: an AP depolarizes an area of the plasma membrane, which causes an AP next to that AP, which then causes an AP next to that AP.....
Describe how the v-gated sodium channels and the v-gated potassium channels work in tandem to construct an action potential.
The V-gated sodium channels flicker open first and let Na+ into the cell, thereby depolarizing it (front half of the wave). The wave peaks at +30 mV when the Na+ channels close and before the K+ channels open. Immediately after the V-gated sodium channels close, the V-gated potassium channels open and let potassium out of the cell which repolarizes it (back half of the wave).
The V-gate sodium channels open first bc they are more sensitive
Once an action potential is initiated, what are its characteristics?
Action potentials: are all or none (digital) events, very fast, exclusive to excitable cells, once they start they will self-propagate all the way down to the end of the cell, cannot summate
How is an action potential channeled into the cell and how does it also keep going down the sarcolemma after encountering such a channel?
An AP is channeled into the cell through T tubules
Some of the AP can go down the T tubule and some of the AP can continue down the sarcolemma to the next T tubule
Describe the key shape of an action potential.
A wave that goes up, stops, then goes back down
About how long does an action potential last on a given location of sarcolemma?
About 1 ms
What allows the initial upswing (depolarization) and when, how and why does it end?
Depolarization is caused by the V-gated sodium channels opening and letting sodium into the cell, thus making the inside of the cell more positive (membrane potential becomes positive)
It ends when the V-gated sodium channels close
What then causes the repolarization?
Repolarization is caused by the V-gated potassium channels opening and letting potassium out of the cell, thus returning the membrane potential to its resting value
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