BioPhysics PMU Qs

1. What is the necessary condition for generation of spike potentials in smooth muscle cells?

a) sufficient intra-cellular calcium deposits;

b) reaching membrane depolarization threshold;

c) sufficient density of voltage-gated Na+ channels.

b) reaching membrane depolarization threshold

2. Spike potentials in smooth muscles are defined as:

a) action potentials;

b) slow waves;

c) Ca2+ equilibrium potentials.

a) action potentials

3. Smooth muscle tissue is build of this type of cells:

a) cylindrical cells;

b) spindle-shaped cells;

c) relatively small hexagonally-shaped cells.

b) spindle-shaped cells

4. "Slow waves" are present in:

a) gastrointestinal smooth muscle tissue;

b) bronchial smooth muscle tissue;

c) arterial smooth muscle tissue.

a) gastrointestnal smooth muscle tissue

5. Slow waves are changes in the membrane potential in certain smooth muscles:

a) due to input from the nervous system;

b) not due to stimuli from the nervous system or endogenous substances;

c) due to endogenous substances.

b) not due to stimuli from the nervous system or endogenous substances

6. Is there a functional relationship between slow waves and spike potentials in smooth muscle cells?

a) yes, slow waves can trigger spike potentials;

b) there is no known functional dependence;

c) yes, spike potentials can trigger slow waves.

a) yes, slow waves can trigger spike potentials

7. The dynamics of ion flow during spike potentials is:

a) Na+ influx → depolarization, K+ efflux → repolarization;

b) Ca2+ influx → depolarization, K+ efflux → repolarization;

c) Ca2+ efflux → depolarization, Na+ influx → repolarization.

b) Ca2+ influx → depolarization, K+ efflux → repolarization;

8. In the cytosol Ca2+ ions bond to, and activate a protein which plays a critical role in the contraction of the smooth muscle. This protein is:

a) calmodulin;

b) tropomyosin;

c) troponin C.

a) calmodulin

9. Which of the following muscles do not have an ordered sarcomere structures?

a) skeletal muscles;

b) cardiac muscle;

c) smooth muscles.

c) smooth muscles

10. Which ion channels permit the Ca2+ ion influx, necessary for the spontaneous phasic contractions of smooth muscles?

a) receptor-regulated channels (triggered by ligands);

b) voltage-gated (membrane potential dependent);

c) stretch-regulated (mechanical forces on the membrane).

b) voltage gated (membrane potential dependent)

11. What type of contraction results in smooth and striated muscles when the intervals between consecutive action potentials are shorter than the duration of muscle fiber contractions?

a) single contraction;

b) phasic contractions;

c) complete or incomplete tetanus.

c) complete or incomplete tetanus

12. Which is the best description of the membrane potential of striated muscles when there are no muscle contractions?

a) rhythmic low frequency fluctuations below threshold excitation- formation for slow waves;

b) steady resting potential;

c) slow depolarization initiated from pacemaker cells.

b) steady resting potential

13. What is the source of Ca2+ needed for the contraction of striated skeletal muscles?

a) from intracellular Ca2+ depots;

b) influx of Ca2+ from the extracellular fluid into the sarcoplasm, which leads to additional Ca2+ release form intracellular depots;

c) through suppression of the activity of the calcium pumps (which remove intracellular Ca2+).

a) from intracellular Ca2+ depots

14. What type of membrane channels are activated during action potential propagation along the sarcolemma of striated muscle cells?

a) voltage-gated sodium channels;

b) calcium channels, regulated by ryanodine receptors;

c) voltage-dependent calmodulin receptors.

a) voltage-gated sodium channels

15. The sarcoplasmic reticulum of smooth muscle cells can be characterized as:

a) very elaborate;

b) moderately developed;

c) not elaborate.

c) not elaborate

16. Are there motor endplates in smooth muscle tissues?

a) yes;

b) no;

c) sometimes.

b) no

17. Phasic contraction in smooth muscle cells are responsible for:

a) peristaltic movement;

b) the heartbeat;

c) release of neurotransmitter molecules.

a) peristaltic movement

18. The existence of "slow waves" in the membrane potential is characteristic for:

a) phasic smooth muscle cells;

b) tonic smooth muscle cells;

c) neurons.

a) phasic smooth muscle cells

19. Blood vessels are predominately build of:

a) tonic smooth muscle tissue;

b) phasic smooth muscle tissue;

c) satiated muscle tissue.

a) tonic smooth muscle tissue

20. Activation of the enzyme myosin light chain kinase (MLCK) leads to:

a) contraction in smooth muscle cells;

b) relaxation in smooth muscle cells;

c) initiation of slow waves.

a) contraction in smooth muscle cells

21. The basic contraction unit in muscle tissues is:

a) the smooth muscle cell;

b) the smooth muscle fiber (myofibril);

c) the fiber bundle, wrapped in connective tissue (fascicle).

b) the smooth muscle fiber (myofibril)

22. Choose the correct statement:

a) in visceral smooth muscle tissue, found in hollow organs, fiber bundles are innervated together (as a single unit), and individual cells communicate via nexuses (gap junctions);

b) in visceral smooth muscles, found in hollow organs, each muscle cell is innervated individually (as a multi-unit), and individual cells communicate via gap junctions;

c) in visceral smooth muscles, found in hollow organs, each muscle cell is innervated individually, and individual cells do not communicate.

a) in visceral smooth muscle tissue, found in hollow organs, fiber bundles are innervated together (as a single unit), and individual cells communicate via nexuses (gap junctions);

23. Choose the set of characteristics that describes best smooth muscle contractions:

a) voluntary, slow, large energy expenditure;

b) involuntary, fast, low energy expenditure;

c) involuntary, slow, low energy expenditure.

c) involuntary, slow, low energy expenditure

24. The thin myofilaments in smooth muscle cells are build of:

a) 4 types of contractile proteins;

b) 2 types of contractile proteins;

c) 3 types of contractile proteins.

b) 2 types of contractile proteins

25. The basis of the thin myofilaments in smooth muscle tissue is the protein:

a) myosin;

b) actin;

c) troponin.

b) actin

26. The basis of the thick myofilaments in smooth muscles is the protein:

a) myosin;

b) actin;

c) tropomyosin.

a) myosin

27. Choose the correct statement regarding discrete (multi-unit) smooth muscles:

a) in discrete smooth muscle tissue, found in hollow organs, each cell is innervated separately, and individual cells communicate via nexuses (gap junctions);

b) in discrete smooth muscles each cell is innervated individually, thus cells do not communicate directly;

c) in discrete smooth muscles, found in hollow organs, fibers are innervated together in bundles, and individual cells communicate via nexuses (gap junctions).

b) in discrete smooth muscles each cell is innervated individually, thus cells do not communicate directly;

28. In smooth muscles fibers the ratio between actin and myosin (thin/tick) fibers is:

a) random;

b) 5:1 to 13:1;

c) always 6:1.

b) 5:1 to 13:1

c)-> stiated muscle

29. Thin myofilaments in smooth muscle tissues are build of the following proteins:

a) myosin, actin, titin, and troponin;

b) actin and tropomyosin;

c) actin, titin, and calmodulin.

b) actin and tropomyosin;

30. What is the spacial orientation of the smooth muscle contractile apparatus?

a) random orientation;

b) aligned in one direction, along the length of the fiber;

c) aligned in two perpendicular directions.

a) random orientation;

31. What is the source of Ca2+ needed for the contraction of the smooth muscles?

a) from the extracellular medium, where calcium concentration is much greater than in the intracellular space;

b) from in the intracellular depots, found in the sarcoplasmic reticulum;

c) both a. and b.

c) both a & b

32. What is the role of Ca2+ in the smooth muscle contraction?

a) bonds to regulatory protein calmodulin;

b) bonds to the myosin molecule;

c) Ca2+ does not affect smooth muscle contraction.

a) bonds to regulatory protein calmodulin;

33. Which intracellular factors lead to a smooth muscle relaxation?

a) factors that activate the enzyme myosin light chain phosphatase;

b) factors that inhibit the enzyme myosin light chain phosphatase;

c) factors that activate the enzyme myosin light chain kinase.

a) factors that activate the enzyme myosin light chain phosphatase;

34. Which intracellular factors lead to a smooth muscle contraction?

a) factors that activate the enzyme myosin light chain phosphatase;

b) factors that inhibit the enzyme myosin light chain phosphatase;

c) factors that activate the enzyme myosin light chain kinase.

c) factors that activate the enzyme myosin light chain kinase.

35. What is the role of the enzyme myosin light chain kinase (MLCK) in the smooth muscle contraction?

a) it shortens the thin myofilaments and, after phosphorylation, it bends actin into a spiral;

b) it phosphorylates the 20-kDa myosin light chain (MLC 20) of the myosin molecule, allowing for cross-bridge formation between thin and thick myofilaments;

c) it interacts with ATP and the thin myofilaments, delivering energy for the contraction.

b) it phosphorylates the 20-kDa myosin light chain (MLC 20) of the myosin molecule, allowing for cross-bridge formation between thin and thick myofilaments;

36. What is the role of the enzyme myosin light chain phosphatase (MLCP) in the smooth muscle relaxation?

a) after contraction, it lengthens the thick myofilaments;

b) it de-phosphorylates the 20-kDa myosin light chain (MLC 20) of the myosin molecule, disrupting the bonding of myosin with the dense bodies of the membrane;

c) it de-phosphorylates the 20-kDa myosin light chain (MLC 20) of the myosin molecule, disrupting the cross-bridge formation between thin and thick fibres.

c) it de-phosphorylates the 20-kDa myosin light chain (MLC 20) of the myosin molecule, disrupting the cross-bridge formation between thin and thick fibres.

37. What is the function of protein calmodulin for the smooth muscle contraction?

a) it forms a complex with four calcium ions, which activates the enzyme myosin light chain kinase

(MLCK);

b) does not affect smooth muscle contraction;

c) it transports Ca2+ from the cellular membrane to the protein troponin C.

a) it forms a complex with four calcium ions, which activates the enzyme myosin light chain kinase

(MLCK);

38. The electro-mechanical coupling of smooth muscles is:

a) muscle contraction stimulated with electric current;

b) the relation between action potential and subsequent increase of intracellular Ca2+ leading to contraction;

c) the directed movement of Ca2+ (electric current) in the cytosol towards the contractile apparatus (mechanical).

b) the relation between action potential and subsequent increase of intracellular Ca2+ leading to contraction;

39. What is a spike potential?

a) a rapid change in the membrane potential due to a slow wave;

b) action potential in certain smooth muscle cells;

c) electric phenomenon due to re-orientation of the myofilaments in the smooth muscle cell.

b) action potential in certain smooth muscle cells;

40. Is there a relationship (and if there is then what type) between spike potentials and the Ca2+ concentration in the cytosol?

a) yes there is. Spike potentials are caused in part by Ca2+ influx and that leads to increase in the intracellular calcium;

b) no;

c) yes, there is. Spike potentials cause Ca2+ efflux which leads to decrease of the calcium concentration in the cytosol.

a) yes there is. Spike potentials are caused in part by Ca2+ influx and that leads to increase in the intracellular calcium;

41. Is there a relationship (and what type) between spike potentials and the strength of contraction of smooth muscles?

a) no;

b) yes, it is proportional. The greater the number of spike potentials the stronger the contraction;

c) Yes. An increased number of spike potentials will decrease the strength of muscle contraction.

b) yes, it is proportional. The greater the number of spike potentials the stronger the contraction;

42. Is there a difference in the properties of phasic and tonic smooth muscle contractions?

a) no, they are two names for the same basic process;

b) yes. Phasic contractions occur with certain repetition of few times per minute, and tonic contractions rise slowly and can last many minutes;

c) yes. Tonic contractions occur with regular frequency and amplitude, and phasic contractions are slow and can last many minutes.

b) yes. Phasic contractions occur with certain repetition of few times per minute, and tonic contractions rise slowly and can last many minutes;

43. Spike potentials are found in:

a) hepatocytes;

b) cardiac contractions;

c) phasic smooth muscle contractions.

c) phasic smooth muscle contractions.

44. Tonic smooth muscle contractions are characterized by:

a) generation of autonomous action potential;

b) the lack autonomous action potential;

c) positive membrane potential.

b) the lack autonomous action potential;

45. Phasic smooth muscles are characterized by:

a) their steady membrane potential;

b) their function to maintain the tonus in blood vessels;

c) sinusoidal variation in the membrane potential.

c) sinusoidal variation in the membrane potential.

46. During smooth muscle contraction, the concentration Ca2+ in the cytosol increases to:

a) 10^-5 mol/l;

b) 10^-7 mol/l;

c) 10^7 mol/l.

a) 10^-5 mol/l;

47. Spike potentials in smooth muscles provide:

a) Ca2+ influx from the extracellular space into the cytosol;

b) Ca2+ efflux from the cytosol into the extracellular space;

c) bidirectional transfer of Ca2+ across the membrane, leading to equilibrium.

a) Ca2+ influx from the extracellular space into the cytosol;

48. In smooth muscle cells, the complex 4Ca∙Calmodulin activates:

a) the light chain of myosin phosphatase;

b) myosin light chain kinase (MLCK);

c) the Ca2+ regulated K+ channels.

b) myosin light chain kinase (MLCK);

49. Ca2+ pumps work to:

a) increase Ca2+ concentrations in the cytosol;

b) decrease Ca2+ concentrations in the cytosol;

c) do not affect cytosol concentrations of Ca2+.

b) decrease Ca2+ concentrations in the cytosol;

50. The two known Ca2+ depots in the sarcoplasmic reticulum (IP3-regulated and Ryanodineregulated) are:

a) independent of each other;

b) one depot with two different channels;

c) dependent on the membrane potential.

a) independent of each other;

51. What are the elastic properties of muscles?

a) the ability to stretch;

b) the ability to return to initial size after a stretch;

c) the ability to contract.

b) the ability to return to initial size after a stretch;

52. In the living body all muscles maintain certain level of tension called tonus. During contraction this tonus will:

a) increase;

b) decrease;

c) stay the same.

a) increase

53. Why are smooth muscles (SM) called autonomous?

a) because SM react to external stimuli;

b) because excitations can be generated within the SM tissue;

c) because SM can remain de-excited for long periods.

b) because excitations can be generated within the SM tissue;

54. Smooth muscle contraction is triggered by increased intra-cellular concentration of this type of ions:

a) K+;

b) Ca2+;

c) Na+.

b) Ca2+

55. In the human body, smooth muscles are found in:

a) most of the internal organs;

b) the skeletal muscles;

c) the pacemaking tissue of the heart muscle.

a) most of the internal organs;

56. The structural muscle tissue found in arterial walls is of this type:

a) phasic smooth muscle;

b) tonic smooth muscle;

c) striated muscle cells working in tandem with tonic smooth muscle cells.

b) tonic smooth muscle;

57. Is there a relationship between slow wave membrane potentials and the contractions in smooth muscle cells?

a) yes, slow waves are related with tonic contractions;

b) yes, slow waves are related with phasic contractions;

c) there is no relation between slow waves and contractions.

b) yes, slow waves are related with phasic contractions;

58. What is characteristic about the membrane potential of the stomach?

a) rhythmic fluctuations with low frequency and below threshold;

b) constant potential at rest;

c) depolarization reaching threshold once every second.

a) rhythmic fluctuations with low frequency and below threshold;

59. In smooth muscle cells, all intra-cellular factors that activate myosin light chain kinase (MLCK) will cause:

a) relaxation;

b) contraction;

c) neither

b) contraction

60. Ion channels are:

a) temporary openings (pores) in the cellular membrane;

b) membrane proteins that span across the lipid bilayer and come in contact with the extra- and intracellular environments;

c) mobile membrane proteins that move across the lipid bilayer from the extracellular into the intracellular space.

b) membrane proteins that span across the lipid bilayer and come in contact with the extra- and intracellular environments;

61. What is the role of the electrostatic filter in ion channels?

a) it changes the ion channel state: open or closed;

b) it selects the ion species that can pass through the channel;

c) it interacts with the electrically charged heads of the phospholipid molecules in order to change conformation.

b) it selects the ion species that can pass through the channel;

62. Is it possible for Cl- ions to pass through a Ca2+ ion channel?

a) no, because Cl- ions are too large to fit the narrow channel;

b) yes, they can;

c) no, because the Ca2+ ion channel has an electrostatic selectivity filter with negative charge.

c) no, because the Ca2+ ion channel has an electrostatic selectivity filter with negative charge.

63. How many gates do voltage-gated Na+ channels have?

a) one;

b) two;

c) three.

b) two

64. Which of the following membrane conditions activate the voltage-gated (potential-dependent) ion channels?

a) depolarization of the plasma membrane;

b) hyper-polarization of the plasma membrane;

c) keeping the membrane potential unchanged for period of 50 ms.

a) depolarization of the plasma membrane;

65. Which of the following combinations of factors determine the activation time of the voltage-gated ion channels?

a) the membrane potential and the pH of the cytosol;

b) the level of hyper-polarization of the membrane and the specific channel gate kinetics;

c) the level of membrane depolarization and the specific ion channel kinetics.

c) the level of membrane depolarization and the specific ion channel kinetics.

66. What activates ligand-gated (receptor-regulated) ion channels?

a) changes in the membrane potential;

b) interaction between the corresponding ligand and the receptor, regulating the ion channel;

c) the process of internalization of the receptor.

b) interaction between the corresponding ligand and the receptor, regulating the ion channel;

67. What prevents inorganic ions from moving through the phospholipid membrane?

a) the equal concentrations of ion species on both sides of the membrane (isotonicity);

b) inorganic ions are water-soluble. The phospholipid bilayer does not permit the passage of watersoluble substances;

c) the ion passage is prevented by the higher hydrostatic pressure inside the cell.

b) inorganic ions are water-soluble. The phospholipid bilayer does not permit the passage of watersoluble substances;

68. Are ion channels completely impermeable for all but the ion species that give the channel's name?

a) no, other similar ions can pass with low probability;

b) yes, they permit only the ion species that give the channel's name;

c) no, large organic molecule can also pass through the channels.

a) no, other similar ions can pass with low probability;

69. Is ion channel traffic regulated and how?

a) no, ion traffic is not regulated;

b) ion traffic is regulated through conditional gating mechanisms;

c) ion traffic is regulated by pressure gradients.

b) ion traffic is regulated through conditional gating mechanisms;

70. Which of the following descriptions refers to ion channels?

a) a random, temporary formation of pores in the lipid bilayer;

b) protein structures that transport ions across the membrane with the expense of energy;

c) protein structures that allow passive transport of inorganic ions.

c) protein structures that allow passive transport of inorganic ions.

71. Choose the best fitting description for ion channels from the following:

a) membrane protein structures that span across the membrane, and under certain conditions provide selective ion transport between extra and intra cellular spaces;

b) membrane lipid structures that span across the membrane, and under certain conditions allow a water-filled passage between extra and intra cellular spaces;

c) membrane protein structures that provide uninterrupted ion transport between intra and extra cellular spaces.

a) membrane protein structures that span across the membrane, and under certain conditions provide selective ion transport between extra and intra cellular spaces;

72. What forces drive ions through the ion channels?

a) electrochemical gradients;

b) hydrostatic pressure;

c) osmotic pressure.

a) electrochemical gradients;

73. What type of transport takes place through ion channels when they are activated:

a) passive;

b) active;

c) passive when moving in, and active when moving out of the cell.

a) passive;

74. Which ion types can pass through the calcium-activated potassium channels?

a) calcium ions;

b) potassium ions;

c) sodium ions.

b) potassium ions

75. Depolarization of the plasma membrane activates this type of ion channels:

a) receptor-regulated (ligand-gated) channels;

b) voltage-gated channels;

c) none of the above.

b) voltage-gated channels;

76. Nifedipine and Verapamil are channel blockers for this type of ions:

a) calcium membrane channels;

b) sodium channels located on cellular organelles;

c) potassium membrane channels.

a) calcium membrane channels;

77. The repolarization phase of spike potentials is due to the opening of this type of channels:

a) calcium-activated potassium channels;

b) voltage-gated calcium channels;

c) sodium channels.

a) calcium-activated potassium channels;

78. TTX is a blocker of this type of channels:

a) voltage-gated membrane sodium channels found in neurons;

b) potassium membrane channels found in smooth muscle tissue with spontaneous bioelectric activity;

c) non-activating sodium channels found in the cardiac sinoatrial node.

a) voltage-gated membrane sodium channels found in neurons;

79. The passive trans-membrane transport of neutral molecules, when possible, is driven by:

a) their electrochemical gradient;

b) their electrical gradient;

c) their concentration gradient.

c) their concentration gradient.

80. Choose the correct statement regarding ligand-gated ion channels:

a) they are inactivated by complementarity;

b) they are activated by changes in the membrane potential;

c) the ligand-receptor interaction leads to conformational changes in the protein structure.

c) the ligand-receptor interaction leads to conformational changes in the protein structure.

81. Conduction of inorganic ions through the plasma membrane is carried by:

a) endocytosis;

b) narrow water-filled channels with diameter of 0.3 - 0.65nm;

c) phagocytosis.

b) narrow water-filled channels with diameter of 0.3 - 0.65nm;

82. Ion transport through the ion channels is:

a) unidirectional;

b) active;

c) passive.

c) passive.

83. During the resting state of the cell, the Na+ electrochemical gradient points:

a) from the extracellular into the intracellular space;

b) from the intracellular into the extracellular space;

c) in both directions.

a) from the extracellular into the intracellular space;

84. The bonding of a specific channel blocker with a target ion channel will result in:

a) inhibition of the passive transport of the particular ion species;

b) inhibition of the active transport of the particular ion species;

c) inhibition of the passive ion transport in the entire body.

a) inhibition of the passive transport of the particular ion species;

85. The phospholipid bilayer of the plasma membrane allows passive diffusion of:

a) small hydrophobic molecules: oxygen, nitrogen, and carbon dioxide;

b) small inorganic ions: sodium, potassium, and magnesium;

c) large organic molecules: amino acids, peptides, and glucose.

a) small hydrophobic molecules: oxygen, nitrogen, and carbon dioxide;

86. Which of the following names of ion channel structures is not part of the accepted terminology?

a) narrow tunnel;

b) opening;

c) gating mechanism.

b) opening;

87. The default state of ion channels is:

a) open;

b) closed (deactivated);

c) inactivated.

b) closed (deactivated)

88. The type of transport through the ion channels is called:

a) active;

b) passive, driven by existing gradients;

c) passive for some ions, and active for others.

b) passive, driven by existing gradients;

89. What is the electric charge of the narrow tunnels in ion channels?

a) positive;

b) negative;

c) opposite to the electric charge of the ion species that pass through the channel.

c) opposite to the electric charge of the ion species that pass through the channel.

90. In which of the following cases will a voltage-gated (potential-dependent) ion channel be activated?

a) when the membrane potential is higher than the activation threshold for the ion channel

b) when the membrane potential is at resting level

c) when the membrane potential is lower than the activation threshold for the ion channel

a) when the membrane potential is higher than the activation threshold for the ion channel

91. Trans-membrane ion transport through ion channels is driven by:

a) osmotic gradients;

b) equilibrium potentials;

c) electrochemical gradients.

c) electrochemical gradients.

92. Ion channels are (choose the best):

a) integral proteins;

b) transmembrane proteins;

c) peripheral proteins.

b) transmembrane proteins;

93. An ion channel that could be activated by a hormone, neurotransmitter, mediator, or other biologically active substance is called:

a) potential-dependent channels;

b) ligand-gated channels;

c) Ca2+ dependent channels.

b) ligand-gated channels;

94. Which of the following types of ion channels permit calcium, needed for the phasic contractions in smooth muscles, into the cell?

a) ligand-gated channels;

b) voltage-gated channels;

c) stretch-gated channels (mechano-sensitive).

b) voltage-gated channels;

95. The sarcomere is:

a) a protein involved in the contraction of striated muscle fibres;

b) an element of the striated muscle fiber, located between two Z-discs;

c) a structure that produces second messengers in muscle cells.

b) an element of the striated muscle fiber, located between two Z-discs;

96. Thin myofilaments in striated muscle cells are composed of:

a) 4 type of proteins;

b) 1 type of protein;

c) 3 types of proteins.

c) 3 types of proteins.

97. The major protein component of the thin myofilaments in striated muscle cells is:

a) myosin;

b) actin;

c) troponin.

b) actin;

98. The major protein component of the thick myofilaments in striated muscle cells is:

a) myosin;

b) actin;

c) troponin.

a) myosin

99. In skeletal muscles the ratio between actin and myosin filaments is:

a) undetermined;

b) it varies from 6:1 to 15:1;

c) always 6:1.

c) always 6:1.

100. The myosin molecule in striated muscles has:

a) two active sites: for bonding with Tropomyosin C, and ATP;

b) three active sites: for bonding with F - actin, Ca2+, and ATP;

c) two active sites: for bonding with F - actin, and ATP.

c) two active sites: for bonding with F - actin, and ATP.