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.
Spike potentials in smooth muscles are defined as:
a) action potentials;
b) slow waves;
c) Ca2+ equilibrium potentials.
Smooth muscle tissue is build of this type of cells:
a) cylindrical cells;
b) spindle-shaped cells;
c) relatively small hexagonally-shaped cells.
“Slow waves” are present in:
a) gastrointestinal smooth muscle tissue;
b) bronchial smooth muscle tissue;
c) arterial smooth muscle tissue.
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.
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
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.
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
Which of the following muscles do not have an ordered sarcomere structures?
a) skeletal muscles;
b) cardiac muscle;
c) smooth muscles.
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).
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
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
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+
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
The sarcoplasmic reticulum of smooth muscle cells can be characterized as:
a) very elaborate;
b) moderately developed;
c) not elaborate
Are there motor endplates in smooth muscle tissues?
a) yes;
b) no;
c) sometimes
Phasic contraction in smooth muscle cells are responsible for:
a) peristaltic movement;
b) the heartbeat;
c) release of neurotransmitter molecules
The existence of “slow waves” in the membrane potential is characteristic for:
a) phasic smooth muscle cells;
b) tonic smooth muscle cells;
c) neurons
19. Blood vessels are predominately build of:
a) tonic smooth muscle tissue;
b) phasic smooth muscle tissue;
c) satiated muscle tissue
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
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).
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.
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.
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.
The basis of the thin myofilaments in smooth muscle tissue is the protein:
a) myosin;
b) actin;
c) troponin
The basis of the thick myofilaments in smooth muscles is the protein:
c) tropomyosin
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)
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.
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
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.
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.
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.
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.
Which intracellular factors lead to a smooth muscle contraction?
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
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.
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.
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;
the directed movement of Ca2+ (electric current) in the cytosol towards the contractile apparatus (mechanical).
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.
0. 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;
c) yes, there is. Spike potentials cause Ca2+ efflux which leads to decrease of the calcium concentration in the cytosol.
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
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.
Spike potentials are found in:
a) hepatocytes;
b) cardiac contractions;
c) phasic smooth muscle contractions
Tonic smooth muscle contractions are characterized by:
a) generation of autonomous action potential;
b) the lack autonomous action potential;
c) positive membrane potential.
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.
During smooth muscle contraction, the concentration Ca2+ in the cytosol increases to:
a) 10-5 mol/l;
b) 10-7 mol/l;
c) 107 mol/l.
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.
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.
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+
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.
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.
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
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.
. Smooth muscle contraction is triggered by increased intra-cellular concentration of this type of ions:
.
a) K+
b) Ca2+;
c) Na+
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.
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
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.
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.
In smooth muscle cells, all intra-cellular factors that activate myosin light chain kinase (MLCK) will cause:
a) relaxation;
b) contraction;
c) neither
