HBY 531 MEDICAL PHYSIOLOGY

Lecture Exam 1

2004

Section 1: Answer the following using:

A = increase

B = not change

C = decrease

1. If NaCl is added to the normal solution bathing a cell, cell volume will _____C__________.

2. If a neurotransmitter causes a reduction in cellular Na/K ATPase activity, steady state [Ca⁺²]_i will ______A_________.

3. Using the single channel patch clamp technique, it is seen that increasing [Ca⁺²] at the intracellular face of a K⁺-channel protein causes the fraction of time spent in the open state to increase. In the cell that was patch clamped, a rise in intracellular [Ca⁺²] would _______A_________ the membrane K⁺-conductance due to this channel.

4. Assume E_Cl = -70 mV. If a cell’s resting voltage is caused to abruptly change from -70 mV to -80 mV, over the next few minutes [Cl^-]_i will ________C_______.

5. A nerve axon is isolated and its action potential recorded. The voltage dependent sodium conductance is partially blocked with TTX. Assuming another action potential can be generated, the presence of TTX will cause action potential duration to ______A_________.

6. When a nerve cell membrane is slowly depolarized from -70 mV to -20 mV, the Na⁺-channel inactivation gate open probability, h, will _______C________.

7. An unmylinated axon is exposed to a hydrophobic chemical that inserts into its membrane and causes the membrane capacitance to increase from 1 :F/cm² to 2 :F/cm². Action potential propagation velocity will _______C_______.

8. Curare blocks ACh-Rs and as a consequences the amplitude of MEPPs will _______C________.

9. At a synapse in the CNS, an increase in presynaptic action potential frequency causes an increase in outward current in the postsynaptic cell. As a result, postsynaptic action potential frequency will ________C_______.

10. During contractile activity of skeletal muscle cell, creatine levels will ______A_________.

11. In skeletal muscle, an increase in external Ca²⁺-concentration will cause twitch amplitude to _______B________.

Section 2: For each of the following, choose the single best response.

12. A solution is made containing (in mM): NaCl =100; CaCl₂ =50; sucrose 50. Assuming osmotic coefficients are unity, the osmolarity of this solution is

A. 200 mOsm

B. 250 mOsm

C. 300 mOsm

D. 400 mOsm

E. 500 mOsm

13. A cell, initially in equilibrium, contains concentrations of permeants s_i =150 mM and impermeants S_i =150 mM. This cell is transferred to a large bath containing S_o =300 mM and s_o = 0. The ratio of final volume to initial volume is

A. ½

B. 2

C. 3

D. 1/3

E. 1

14. Which of the following is true of a biomembrane?

A. The lipid phase is permeable to ions

B. The lipid phase is permeable to glucose

C. The lipid phase is impermeable to small hydrophobic solutes

D. The proteins mediate the transport of ions

E. All of the above

15. Primary (ATP driven) active transport is directly used to control the intracellular concentration of

A. sodium

B. potassium

C. hydrogen

D. calcium

E. All of the above.

16. Membrane capacitance

A. increases with voltage.

B. increases with charge.

C. depends primarily on membrane proteins.

D. depends primarily on membrane lipids.

E. mediates ion movement across the membrane.

17. The conductance of a biomembrane is due to

A. The lipid bilayer.

B. The dielectric constant of oil.

C. Integral membrane proteins.

D. The surface charge.

E. The membrane voltage.

Questions 18-19 refer to the figure below:

Intracellular Extracellular

[Na]_o = 144 mM

[K]_o = 4 mM

[Cl]_o = ?

[Ca]_o = 2 mM

g_K = g_Cl = 1.1 mS/cm²

g_Na = 0.025 mS/cm²

g_Ca = 0.01 :S/cm²

18. R_i =

A. -92.5 mV

B. -89 mV

C. -60 mV

D. -80 mV

E. -69.5 mV

19. [A]_i =

A. 147 mM.

B. 149 mM.

C. 151 mM.

D. 153 mM.

E. 155 mM

20. At the peak of a nerve action potential, the ratio g_Na/g_K = 15. If E_Na = +60 mV and E_K = -100 mV, what is the voltage at the action potential peak?

A. +60 mV.

B. +50 mV.

C. +40 mV.

D. +30 mV.

E. +20 mV.

21. Threshold for an action potential is

A. the current at which the voltage switches from negative to positive.

B. the current at which the voltage switches from positive to negative.

C. the voltage at which the current switches from inward to outward.

D. the voltage at which the current switches from outward to inward.

E. the voltage at which the current change is zero.

22. During the relative refractory period,

A. g_Na is elevated over rest.

B. threshold is more positive than at rest.

C. inward current exceeds outward current.

D. g_K is inactivated.

E. none of the above is true.

23. Which of the following is a role of action potentials?

A. Regulation of contraction.

B. Signal for exocytosis.

C. Transmission of information.

D. Signal for contraction.

E. All of the above.

24. Which of the following would increase action potential propagation velocity?

A. An increase in axon length.

B. An increase in membrane capacitance.

C. An increase in peak g_Na.

D. An increase in peak g_K.

E. An increase in resistivity of axoplasm.

25. Given the data below for length constant 8 and capacitance per unit length C_m, if all else is equal, which skeletal muscle fiber would have the most rapid action potential propagation velocity?

A. 8 = 2.0 mm, C_m = 10 nF/mm.

B. 8 = 1.5 mm, C_m = 10 nF/mm.

C. 8 = 2.0 mm, C_m = 15 nF/mm.

D. 8 = 1.5 mm, C_m = 15 nF/mm.

E. 8 = 2.0 mm, C_m = 20 nF/mm.

26. Myasthenia gravis has caused a person to lose a large fraction of their ACh receptors. The miniature end plate potentials (MEPPs) recorded in muscle cells removed from this person will be

A. longer in duration than normal.

B. more frequent than normal.

C. larger in amplitude than normal.

D. smaller in amplitude than normal.

E. the same as normal. .

27. A patient has taken an unknown drug, which has caused muscle stiffness. EMG reveals normal nerve action potential activity but unusually high muscle action potential activity. The drug could be

A. an inhibitor of the ACh-receptor.

B. an inhibitor of presynaptic calcium entry.

C. an inhibitor of ACh synthesis.

D. an inhibitor of ACh breakdown.

E. any of the above.

Questions 28-29 refer to the figure below:

The whole cell patch technique is used to record the post synaptic potential (R_PS) from the cell body of a neuron. When the axon is not stimulated, the following are determined

R_PS = -70 mV

E_Na = +60 mV g_Na = 0.2 mS/cm²

E_K = -90 mV g_K = 1.3 mS/cm²

E_Cl = -70 mV g_Cl = 0 mS/cm²

The following data were obtained by recording R_PS while rapidly stimulating the axon