September 24, 2010 at 2:29 pm #13810biol245Participant
Hi. I need help on the following questions. Please help. Thank you.
1. In a voltage clamp experiment, Hodgkin and Huxley first clamped an axon at 0 mv and then at +60 mV. Assuming ENa+ is +60 mV and EK+ is -80 mV, when compared with the recording obtained when clamped at 0 mV, the recording at +60 mV showed ________ inward current followed by ________ in outward current.
A. increased; a decrease
B. increased; an increase
C. decreased; an increase
D. increased; no change
E. decreased; a decrease
2. If EK is -80 mV, what is the net driving force on K+ when an axon is voltage-clamped at -100 mV?
A. 20 mV inward
B. 180 mV inward
C. 20 mV outward
D. 180 mV outward
E. 0 mV because membrane potential is more negative than the equilibrium potential
3. In the resting, unstimulated neuron, activation gates of most sodium channel are____ inactivation gates of most sodium channels are_____ and activation gates of most voltage-gated potassium channels are ______.
A. closed; open; closed
B. closed; open; open
C. closed; closed; open
D. closed; closed; closed
4. In a voltage clamp experiment, sodium in the extracellular fluid is reduced to a concentration LESS than the intracellular sodium concentration. In this experiment, when membrane potential is clamped at 0 mV:
A. the late sustained current is now inward instead of the normal direction out of the cell
B. the early transient current is now outward and the late sustained current is now inward
C. the early transient current is now inward instead of the normal outward direction.
D. there is no early transient current, either inward or outward when membrane potential is clamped at 0 mV.
E. the early transient current is now outward instead of the normal inward direction.
5. In a typical neuron during the ‘overshoot phase’ of an action potential, for Na+: the electrical (electrostatic) force is _______ and the ‘chemical’ force is_________.
A. zero; inward
B. directed outward; outward
C. zero; outward
D. directed inward; outward
E. directed outward; inward
6. During the ‘falling phase’ of an action potential, membrane permeability of_________ and membrane permeability of__________ compared to the rising phase.
A. Na+ is smaller and K+ is greater
B. Na+ is smaller and K+ is also smaller
C. Na+ is greater and K+ is smaller
D. Na+ is greater and K+ is also greater
7. The _______ refractory period is the period after the peak of an action potential when the possibility of stimulating a second action potential is _________ because the _____________________.
A. relative; depressed; voltage-gated K+ channels are inactivated
B. absolute; completely blocked; voltage-gated Na+ channels are inactivated
C. absolute; depressed; voltage-gated K+ channels are inactivated
D. A & B are both correct
8. In a voltage-clamp experiment, the investigator "clamps" the membrane at a chosen voltage level and measures the _______ required to maintain the membrane at that voltage. This information can be used to calculate changes in membrane ___________.
A. conductance; current
B. current; valency
C. conductance; voltage
D. current; conductance
9. Each Shaker potassium channel is formed by _______________ and each voltage-gated sodium channel is formed by________________.
A. four separate protein subunits; one protein with four similar domains
B. one protein with four similar domains; one protein with four similar domains
C. four separate protein subunits; four separate protein subunits
D. one protein with four similar domains; four separate protein subunits
10. The magnitude of the Na+ current measured during a voltage clamp experiment depends on:
A. the driving force on Na+
B. (Vm – ENa+)
C. membrane conductance for Na+
D. all of the above are correct
E. none of the above: there is no Na+ current during a voltage clamp experiment
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