Physiology QL Flashcards
What is occurring when the length-tension of a single vertebrate striated muscle fiber is maximized?
A. actin filaments are overlapping each other
B. myosin filaments are overlapping each other
C. the Z discs of the sarcomere abut the ends of the myosin filament
D. there is optimal overlapping between the actin and myosin filaments
E. there is minimal overlap between the actin and myosin filaments
D. there is optimal overlapping between the actin and myosin filaments
Excitation-contraction coupling in skeletal muscle involves all of the following events EXCEPT:
A. ATP hydrolysis
B. binding of Ca++ to calmodulin
C. conformational change in dihydropyridine receptor
D. depolarization of the transverse tubule (T tubule) membrane
E. increased Na+ conductance of sarcolemma
B. binding of Ca++ to calmodulin
A single contraction of skeletal muscle is most likely to be terminated by which of the following actions?
A. closure of the postsynaptic nicotinic acetylcholine receptor
B. removal of acetylcholine from the neuromuscular junction
C. removal of Ca++ from the terminal of the motor neuron
D. removal of sarcoplasmic Ca++
E. return of the dihydropyridine receptor to its resting conformation
D. removal of sarcoplasmic Ca++
Which of the following statements about smooth muscle contraction is most accurate?
A. Ca++ independent
B. does not require an action potential
C. requires more energy compared to skeletal muscle
D. shorter in duration compared to skeletal muscles
B. does not require an action potential
Calmodulin is most closely related, both structurally and functionally, to which of the following proteins? A. G-actin B. Myosin light chain C. Tropomyosin D. Troponin C
D. Troponin C
Similarities between smooth and cardiac muscle include which of the following?
A. ability to contract in the absence of an action potential
B. dependence of contraction on Ca++ ions
C. presence of a T tubule network
D. role of myosin kinase in muscle contraction
E. striated arrangement of the actin and myosin filaments
B. dependence of contraction on Ca++ ions
In a normal, healthy muscle, what occurs as a result of propagation of an action potential to the terminal membrane of a motor neuron?
A. opening of voltage-gated Ca++ channels in the presynaptic membrane
B. depolarization of the T tubule membrane follows
C. always results in muscle contraction
D. increase in intracellular Ca++ concentration in the motor neuron terminal
E. all of the above are correct
E. all of the above are correct
Which of the following decreases in length during the contraction of a skeletal muscle fiber? A. A band of the sarcomere B. I band of the sarcomere C. thick filaments D. thin filaments E. Z discs of the sarcomere
B. I band of the sarcomere
A cross-sectional view of a skeletal muscle fiber through the H zone would reveal the presence of what? A. actin and titin B. actin, but no myosin C. actin, myosin, and titin D. myosin and actin E. myosin, but no actin
E. myosin, but no actin
Tetanic contraction of a skeletal muscle fiber results from a cumulative increase in the intracellular concentration of which of the following? A. ATP B. Ca++ C. K+ D. Na+ E. Troponin
B. Ca++
Weightlifting can result in dramatic increase in skeletal muscle mass. This increase in muscle mass is primarily attributable to which of the following?
A. fusion of sarcomeres between adjacent myofibrils
B. hypertrophy of individual muscle fibers
C. increase in skeletal muscle blood supply
D. increase in the number of motor neurons
E. increase in the number of neuromuscular junctions
B. hypertrophy of individual muscle fibers
Which of the following is primarily responsible for the change in membrane potential between the threshold and the peak of the action potential? A. inhibition of the Na+, K - ATPase B. movement of K+ into the cell C. movement of K+ out of the cell D. Movement of Na+ into the cell E. Movement of Na+ out of the cell
D. Movement of Na+ into the cell
Which of the following is primarily responsible for the change in membrane potential between the peak of the action potential and the fall? A. inhibition of the Na+, K+ - ATPase B. movement of K+ into the cell C. movement of K+ out of the cell D. movement of Na+ into the cell E. movement of Na+ out of the cell
C. movement of K+ out of the cell
The delayed onset and prolonged duration of smooth muscle contraction, as well as the greater force generated by smooth muscle compared with skeletal muscle, are all consequences of which of the following?
A. greater amount of myosin filaments present in smooth muscle
B. higher energy requirements of smooth muscle
C. physical arrangement of actin and myosin filaments
D. slower cycling rate of the smooth muscle myosin cross bridges
E. slower uptake of Ca++ ions following contraction
D. slower cycling rate of the smooth muscle myosin cross bridges
An experimental drug is being tested as a potential therapeutic treatment for asthma. Preclinical studies have shown that this drug induces the relaxation of cultured porcine tracheal smooth muscle cells pre-contracted with acetylcholine. Which of the following mechanisms of action is most likely to induce this effect?
A. decreased affinity of troponin C for Ca++
B. decreased plasma membrane K+ permeability
C. increased plasma membrane Na+ permeability
D. inhibition of the sarcoplasmic reticulum Ca++ - ATPase
E. stimulation of adenylate cyclase
E. stimulation of adenylate cyclase (cyclic nucleotides produced by this enzyme stimulates cAMP and remove Ca++ from the cytosol inhibiting contraction)
