During contraction of a skeletal muscle, all of the following occur, EXCEPT A) t
ID: 85423 • Letter: D
Question
During contraction of a skeletal muscle, all of the following occur, EXCEPT A) the H zone becomes more narrow (shorter). B) ATP is hydrolyzed. C) myosin heads bind to actin. D) calcium concentration in the sarcomere increases. E) myoglobin concentration in muscle cells increase. When the myosin heads bind to the active sites on actin. A) the I band gets wider B) the A band becomes more narrow (shorter) C) ATP is hydrolyzed. D) they pivot toward the M line. E) actin shortens. Which of the following acts as an ATPase (splits ATP to ADP P) during the contraction cycle of muscle? A) myosin tail B) actin C) myosin head D) tropomyosin E) troponin The dark lines in striated muscle is caused by A) the organized arrangement of sarcomers in B) the organized arrangement of sarcomeres in myofilaments C) the random arrangement of dense bodies D) the random arrangement of E) the random arrangement of Opening of sodium channels in the membrane of a neuron or muscle cell results in A) hyperpolarization B) depolarization C) repolarization D) increased negative charge inside the membrane E) a resting potential How would a drugs blocks acetylcholine on the motor end plate affect skeletal muscle? A) It would make the muscles more excitable B) It would produce uncontrolled muscle spasms C) It would cause flaccid paralysis (muscles are relaxed and unable to contract) D) It would cause spastic paralysis (muscles are contracted and unable to relax). E) It would have no effect on skeletal muscles. If the synaptic knob (button) of a motor neuron innervating the biceps muscle suddenly became permeable to calcium ions A) the synaptic knob would release sodium ions. B) the synaptic knob would release C) the synaptic knob would release D) the synaptic knob would release E) None of the above.Explanation / Answer
Answer35) The correct answer is option (C).
The anisotropic band is called the A band. There is a lighter region present In the centre of A band known as H zone. During the contraction of a skeletal muscle, H zone becomes more narrow and hydrolysis of ATP takes place.
The sarcoplasmic reticulum stores high concentration of calcium ions. During contraction, nerve impulse stimulates the release of calcium ions from the sarcoplasmic reticulum into the cytosol. Hence, there is increased concentration of calcium ions in the cytosol.
The concentration of myoglobin is also increased that provides oxygen for oxidative phosphorylation which is required to sustain contractions for a longer time.
Answer 36) The correct answer is option (D).
When myosin heads bind to the active sites on actin, they pivot toward the M line. The I becomes more narrow and disappeared. The width of A band remains constant. There is no change in the lengths of actin or myosin filaments.
Answer 37) The correct answer is option (C).
The head portion of the myosin molecule acts as an ATPase during the contraction cycle of muscle. The thin filaments of skeletal muscle are made up of actin, troponin and tropomyosin. The calcium ions bind to the troponin and thereby, the binding sites on actin get exposed for myosin head. During relaxation, troponin binds to the tropomyosin and prevents the contraction of muscles.
Answer 38) The correct answer is option (A).
The ordered arrangement sarcomeres in myofibrils formed the dark lines in striated muscles. These dark lines are known as Z-lines. Myofibrils are the elongated, cylindrical contractile regions present in striated muscles and each myofibril is composed of numerous sarcomeres.
Answer 39) The correct answer is option (B).
The opening of sodium channels in the membrane of a neuron causes depolarization. During repolarization, the sodium channels are closed and potassium channels are opened which causes efflux of potassium ions. Hyperpolarization is caused by the efflux of potassium ions and influx of chlorine ions. The resting membrane potential is regulated by leaky channels and the Na+/K+ pump.
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