Mathias Exam Questions
Cells Course – 1996-1997
25. A red blood cell initially contains 200 mOsm of impermeant solute. It is dropped into a large bath containing 200 mOsm of permeant solute and 100 mOsm of impermeant solute. The steady-state cell volume will:
a. remain constant.
b. increase by 3/2.
c. decrease by 2/3.
d. increase by 2.
e. decrease by ˝.
26. A toxin attacks a cell by inserting a nonselective channel in the membrane, causing the cell’s voltage to depolarize to near 0 mV. As a result, what will happen to cell volume?
a. remain constant
b. increase
c. decrease
d. decrease then increase
e. cannot be determined
27. Which of the following is not a source of energy used by cells?
a. glucose
b. the H+ gradient across mitochondrial membranes
c. ATP
d. The Na+ gradient across the plasma membrane
e. The osmotic gradient across the plasma membrane
28. Which of the following is not true about the way Na+ crosses cell membranes?
a. by diffusion through lipid
b. by active transport through a protein
c. by diffusion through protein channels
d. by exchange for Ca2+ via a protein
e. by exchange for H+ via a protein
29. A Nernst or equilibrium potential:
a. is always negative to the resting voltage
b. is due to diffusion
c. is equal to the resting voltage
d. is always positive to the resting voltage
e. depends on the membrane capacitance.
30. Which of the following would not change the K+ current crossing a cell membrane?
a. a change in intracellular voltage
b. a change in extracellular K+ concentration
c. a change in the open probability of the memberane’s K+ channels
d. a change in the number of the membrane’s K+ channels
e. a change in the membrane’s capacitance
The next two questions refer to the diagram below:
31. What is the concentration and average valence of the intracellular impermeant solutes, Ai?
a. [A]i = 112.5 mM, Z = -0.88
b. [A]i = 99 mM, Z = -1.00
c. [A]i = 120.0 mM, Z = 0.50
d. [A]i = 112.5 mM, Z = 1.00
e. [A]i = 99.0 mM, Z = -0.88
32. Assume the membrane is permeable only to Na+, K+, and Cl-. Given that gK = 2 mS/cm2, gNa = 1 mS/cm2, and gCl = 1 mS/cm2, what is the resting potential? (Assume the coefficient in the Nernst equation is 60 mV.)
a. +60 mV
b. –120 mV
c. –60 mV
d. 0 mV
e. –90 mV
33. The rapid depolarization and overshoot of the axonal action potential is due to:
a. a rapid increase in K+ conductance
b. a rapid increase in Ca2+ conductance
c. a rapid reduction in inactivation of Na+ conductance
d. a rapid inactivation of Na+ conductance
e. a rapid activation of Na+ conductance
34. The relative refractory period is mostly due to:
a. an elevated K+ conductance
b. an elevated Na+ conductance
c. an inactivated K+ conductance
d. an increase in membrane capacitance
e. an influx of Ca2+
35. Given the peak voltage of a membrane action potential is +50 mV; the Na+ equilibrium potential, ENa, is +70 mV; and at the time of the peak voltage, the K+ current, iK, is 20 mA/cm2, what is the Na+ conductance, gNa (S/cm2), at the time of the peak voltage?
a. 10-6 S/cm2
b. 10-3 S/cm2
c. 1 S/cm2
d. 103 S/cm2
e. 106 S/cm2
36. The cardiac ventricular action potential:
a. is of shorter duration than the skeletal muscle action potential
b. does not involve TTX sensitive, voltage dependent Na+ channels
c. involves both T- and L-type Ca2+ channels
d. is generated by the same channels as the nerve action potential
e. is of shorter duration than the smooth muscle action potential
37. Evolution has produced myelinated axons in order to help us:
a. think more rapidly
b. speak more clearly
c. hear more acutely
d. move more rapidly
e. see a wider spectrum of light.
38. A patient has a genetic defect in their axonal Na+ channels such that there is a negative shift in the voltage dependence of their m- and h-gates. Which of the following could not be a direct consequence?
a. the h-gates close more rapidly than m-gates open
b. increased resting inactivation of Na+-channels
c. paralysis
d. a change in threshold voltage
e. weakness
39. A reduction in ACh esterase at the NMJ will cause:
a. a higher frequency of MEPPS
b. a lower frequency of MEPPS
c. a block in transmission of action potentials
d. exceptionally large MEPPS with near normal time courses
e. exceptionally long MEPPS with near normal amplitudes
40. Which of the following is not a property of the Acetylcholine Receptor, ACh-R?
a. it resides in the postsynaptic muscle membrane
b. it is selective for monovalent cations
c. it will gate open and closed after binding 2 ACh
d. it catalyzes the breakdown of ACh to choline and acetate
e. it is the target of the disease myasthenia gravis
41. Which of the following is not part of signaling at a slow synapse?
a. activation or inhibition of an ion channel
b. activation of a G protein
c. binding of a neurotransmitter to a receptor
d. binding of a neurotransmitter to an ion channel
e. release of a neurotransmitter and its rapid (less than 1 msec) diffusion to the postsynaptic membrane
42. A presynaptic nerve terminal releases a neurotransmitter that activates a K+ conductance in the postsynaptic membrane. If the postsynaptic cell body had an initial voltage of –70 mV and ENa = +70 mV, ECl = -70 mV and EK = -90 mV, the new postsynaptic voltage will be:
a. between –70 mV and +70 mV
b. a train of action potentials
c. between –70 mV and –90 mV
d. more negative than –90 mV
e. –70 mV
The next two questions refer to the sketch below:
43. The structure that transmits the signal for contraction to the most interior myofibrils is:
a. a
b. b
c. c
d. d
e. e
44. The structure that ties together the thin filaments is:
a. a
b. b
c. c
d. d
e. e
45. Smooth muscle, in contrast to skeletal and cardiac muscle, force generation requires:
a. an increase in myosin kinase activity
b. cross bridge binding to actin
c. an increase in intracellular Ca2+
d. an action potential
e. an increase in myosin ATPase activity
46. In malignant hyperthermia, inhalation of an anesthetic causes a rapid and sustained increase in body temperature due to heat production from asynchronous contractions of skeletal muscle fibers. This is due to:
a. increased Ca2+ ATPase activity in the SR
b. inactivation of troponin
c. spontaneous Ca2+ release by the Ryanodine receptors
d. inhibition of the ACh receptor channels at the endplate
e. removal of inhibition of the myosin ATPase