PLEASE HELP ME WITH THESE NEUROBIOLOGY QUESTIONS. FOR Q'S THAT NEED PICS, I ATTACHED FILES OF THE PICS... HOPE THEY WORK..
If a neuron is tonically active at rest, how could you change its excitable properties to make it silent at rest?
Question 1 answers
a) Increase the number of calcium-activated neutral channels (CAN).
b) Raise resting membrane potential above threshold.
c) Tonically active cells can not be changed to silent cells at rest.
d) Decrease resting conductance to Na+.
e) Decrease resting conductance to Cl-.
Question 2 text Question 2
A Rover sent to Mars identifies a novel organism with rather unusual concentrations of ions inside and outside of its neurons. The measured values for the external and internal ion concentrations (in millimoles per liter of water) are:
[Na+] inside = 1000; [Na+] outside = 100
[K+] inside = 100; [K+ ] outside = 1000
[Cl-] inside = 1100; [Cl-] outside = 1100
You measure the resting membrane potential and find that it is -58 millivolts. You can infer that:
Question 2 answers
The membrane is permeable only to Cl- at rest.
The membrane is permeable to only Na+ at rest.
The membrane is equally permeable to Na+ and K+ at rest.
The membrane is permeable to all three ions at rest.
The membrane is permeable to Na and Cl- at rest.
Question 3 text Question 3
(2 pts) You discover that the neurons in the organism from Mars in the previous question can fire action potentials that overshoot zero in response to a current injection. Which ion(s) is/are probably responsible for the overshoot during the action potential?
Question 3 answers
Na+
K+
Cl-
K+ and Na+
K+ and Cl-
Question 4 text Question 4
You experimentally inject identical rectangular current pulses into dendrites of two different neurons. We refer to the injection sites as position A for each cell. The diagram below shows the potential change that you measure in each neuron at positions A and at positions B and C which are 100 and 200 microns distant from A respectively. Based upon the voltage data below, choose the true statement.
Inline image E1_05_04.jpg
Question 4 answers
(a) space constant 1 < space constant 2; time constant 1 < time constant 2 (note: read "<" as "is less than", and ">" as "is greater than")
(b) space constant 1 < space constant 2; time constant 1 > time constant 2
(c) space constant 1 < space constant 2; time constant 1 = time constant 2
(d) space constant 1 > space constant 2; time constant 1 < time constant 2
(e) space constant 1 > space constant 2; time constant 1 > time constant 2
Question 5 text Question 5
Suppose that there was a neuron in which: 1) The membrane was 10 times as permeable to K+ as to Na+ and was only permeable to these ions. 2) The concentration of K+ inside the cell is 10 times higher than that outside and 3) The concentration of Na+ outside the cell is 10 times higher than that inside If the membrane potential of the neuron is 0 millivolts, then which of the following must be true. The Goldman equation is shown below. Note -- you may wish to consult the Nernst/Goldman simulator application from the website: (use control-click to open a new page for easy return to blackboard)
Inline image goldman.gif
Question 5 answers
a) At the 0 mV membrane potential, more K+ is flowing across the membrane than Na.
b) If the concentration of Na+ outside is 100mM and the concentration inside is 10mM, then the inside and outside concentrations of K+ must be 10mM and 1mM.
c) The concentration of Na+ outside must equal the concentration of K+ inside.
d) Both a and c are correct.
e) None of the above are true.
Question 6 text Question 6 2 points Save
In response to a current step, the rate of change of the membrane potential over time is determined by the membrane capacitance and the membrane resistance. Why then does the equation for the length constant not contain any measure of capacitance, but only resistance measures?
Question 6 answers
a) The length constant refers only to a time when all of the membrane current is flowing through the resistance rather than through the membrane capacitance.
b) The capacitance only matters at the current injection site, but not at distances farther away from it.
c) The capacitance is the same along the neuron and so cancels out in the equations for the length constant.
d) The membrane time constant is constant, so capacitance does not matter.
e) Both b and c are true.
Question 7 text Question 7
Which of the following statements is FALSE? If all statements are true, pick e.
Question 7 answers
a) The repolarization phase of an action potential is a consequence of both a closing of Na channels and an opening of K channels.
b) The threshold of an action potential depends on the relative amount of current flowing through Na versus K channels.
c) Opening chloride channels in a typical neuron would act to reduce the ability of the neuron to fire action potentials and also increase the resistance of the membrane of the neuron.
d) The Nernst equation describes a situation in which there is no net current across the membrane, so no need for ion pumps to maintain ion concentrations.
e) All of the above are true.
Question 8 text Question 8
The curves below are from two voltage clamp experiments with squid axon with a resting potential of -75 mV in normal seawater. In the lower red trace the clamp voltage was -60 mV; in the upper trace the clamp voltage was +65. The major currents at X, Y, and Z are:
Inline image Voltage Clamp in Ringers.jpg
Question 8 answers
a) inward sodium; inward potassium; outward potassium
b) outward sodium; outward potassium; inward sodium
c) inward potassium; inward sodium; outward sodium
d) outward potassium; outward potassium; inward sodium
e) inward sodium; outward potassium; outward sodium
Question 9 text Question 9 2 points Save
(2 pts) Which of the following will raise the threshold for the firing of an action potential in a typical neuron? Choose e if all will lower the threshold. [Note: raising the threshold makes it more difficult to fire the spike]
Question 9 answers
a) Raising the external concentration of Na+.
b) Lowering the internal concentration of K+.
c) Making the Na+ channels more sensitive to a potential change.
d) Making the K+ channels less sensitive to a potential change.
e) All of the above will lower the threshold for an action potential.
Question 10 text Question 10 2 points Save
You have identified a patient with a genetic disorder that you have reason to believe might be a mutation in an ion channel. The neurons in the patient are excessively active. Which of the following mutations would NOT be a possible explanation for the excessive excitability.
Question 10 answers
(a) A mutation in the S4 region of the Na+ channel that increased how sensitive the m gate in the channel was to a membrane potential increase.
(b) A change in the pore region of the voltage dependent Na+ channel that increased the ion flow through the single channels.
(c) A mutation of the Na+ channel h gate that increased its sensitivity to a membrane potential increase.
(d) A mutation in the voltage dependent K+ channel pore that decreased the flow of K+ through the pore.
(e) A mutation in the promoter region of the voltage dependent Na+ channel gene that increased expression levels of the channel.
Question 11
The five action potentials shown below are all recorded from the same nerve cell axon in response to the identical current pulse shown below. The action potential in red is normal for this cell. The four other traces are action potentials under the influence of 4 different drugs which alter the time constants, tm, th, and tn for the m-gates and h-gates of the sodium channels and the n-gates of the potassium channels. Each drug affects one gate only, either by increasing or decreasing t. Which curve shows the effect of the drug that increases tm but has no effect on any other time constant? (Hint: you may wish to go to the course website and run the tutorial Action Potential Simulator:
Use shift click on this link to open the simulator in a different window.
Inline image Action potentials increased tau2.jpg
Question 11 answers
curve a
curve b
curve c
curve d
Question 12 text Question 12
(2 pts) You performed a patch clamp recording on two different types of sodium channels, A and B with a single channel present in each patch. In response to an 80 mV voltage step, you record a single current trace from each channel type, which is more or less typical. Based upon these traces, shown below, which of the following is FALSE?
Question 12 answers
Channel A activates more rapidly than channel B
Channel B is more permeable to Na+ ions than channel A
Channel A inactivates more rapidly than channel B
Channel A is more permeable to Na+ ions than channel B
Both channels are voltage-gated
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