Physiology I Revision Question for Lecture 3 (Wednesday November 29th 2023)
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Identify the letter of the choice that best completes the statement or answers the question.
(1) Which of the following characteristics are shared by all three types of muscle tissues? (a) each one contains myosin and actin. (b) each one is neurogenic. (c) each one is striated. (d) each one is considered to be under voluntary control. (e) None of these answers.
(2) Troponin (a) binds with calcium to prevent sarcomere shortening. (b) breaks down actin. (c) breaks down myosin. (d) forms the boundaries of a sarcomere. (e) is an enzyme in the sarcomere.
(3) A function of tropomyosin is (a) bind Ca2+. (b) form attachments with myosin cross bridges. (c) prevent myosin cross bridges from attaching to the thin filaments. (d) serve as an ATPase. (e) None of these answers.
(4) According to the sliding-filament mechanism of muscle contraction, the (a) A bands slide in closer between the I bands. (b) thin filaments slide inward toward the center of the A band. (c) Z lines slide in between the T tubules. (d) contractile proteins contract, thus shortening the sarcomere. (e) filaments slide into the lateral sacs of the sarcoplasmic reticulum.
(5) During excitation-contraction coupling, (a) the action potential travels down the transverse tubules. (b) Ca2+ is released from the sarcoplasmic reticulum. (c) Ca2+ is taken up by the sarcoplasmic reticulum. (d) Both (a) and (b) above are correct. (e) All of these answers.
(6) Of the step in excitation-contraction below, which occurs before the others? (a) exposed actin sites bind with myosin cross bridges. (b) sodium channels open in the fiber's membrane. (c) calcium is released from the sarcoplasmic reticulum. (d) tropnin binds calcium. (e) attachment od ATP allows for cross bridge detachment.
(7) Which is not characteristic of cross bridges? (a) they are a component of thin filaments. (b) they are comprised of myosin. (c) they have an actin binding site. (d) they have an ATPase binding site. (e) they provide power stroking.
(8) Which of the following statements concerning cross bridges is incorrect? Cross bridges (a) are formed by the globular heads of the myosin molecules as they protrude from the thick filaments. (b) bend during muscle contraction. (c) bind to actin during muscle contraction. (d) are not found in the I band. (e) bind with troponin and tropomyosin during muscle contraction to pull them away from the actin helical chain.
(9) During a cross-bridge cycle in skeletal muscle, the (a) cross bridge is energized as myosin ATPase activity hydrolyzes ATP. (b) myosin cross bridge is able to bind with an actin molecule when Ca2+ pulls the troponin-tropomyosin complex aside. (c) linkage between actin and the myosin cross bridge is broken at the end of the cross-bridge cycle as Mg2+ binds to the cross bridge. (d) Both (a) and (b) above. (e) All of these answers.
(10) Which of the following is not involved in the relaxation of muscle? (a) when acetylcholine is destroyed by acetylcholinesterase. (b) when there is no longer a local action potential. (c) when the T tubules actively take up the Ca2+ that had been released. (d) when the actin and myosin molecules are no longer bound together. (e) when the troponin-tropomyosin complex slips back into its blocking position.
(12) What would happen if ATP supplies became very low in a muscle cell? (a) tension development would decrease. (b) cross bridges would not detach from actin. (c) possibly contractures. (d) in death, rigor mortis. (e) All these answers.
(13) Why are you able to repeatedly contract and relax your muscles of respiration, allowing you to breathe in and breathe out? (a) As soon as all of the Ca2+ stored in the lateral sacs of the sarcoplasmic reticulum is used up, muscle relaxation occurs. (b) After the muscle cell becomes excited, acetylcholinesterase rapidly destroys acetylcholine. (c) When there is no longer a local action potential in the muscle cell, Ca2+ is actively transported back into the lateral sacs of the sarcoplasmic reticulum, and muscle relaxation occurs. (d) Both (b) and (c) above. (e) All of these answers.
(68) Which of the following is not a determinant of whole muscle tension? (a) the number of muscle fibers contracting. (b) the tension produced by each contracting fiber. (c) the extent of motor-unit recruitment. (d) the frequency of stimulation. (e) the proportion of each motor unit that is contracting at any given time.
(69) During an isotonic contraction of a muscle in the arm (a) filaments do not shorten in the muscle. (b) movement does not occur. (c) the muscle does not change length. (d) the tension in the muscle does not overcome a load. (e) the tension in the muscle remains constant.
(70) The following statement about dopamine is incorrect (a) inhibitory neurotransmitter (b) excitatory neur0transmitter (c) prolactin-inhiting hormone (d) secreted bu the nerve endings of basal ganglia (e) none of the above.
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