Dr Gawad Physiology Course Online Exam - Excitable – Course Lecture 6

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7 MCQs (Only one correct answer)
Each MCQ: 1 mark, Total mark: 7 (you will your result immediately by the web)
Allowed time: 10 min
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dr Mohammed Abel Gawad


Questions and Answers
  • 1. 

    During muscle contraction, all the following is true except:

    • A.

      The binding sites at the actin filaments are activated by Ca.

    • B.

      The sliding filament theory of contraction assumes that sliding of actin continues as long as Ca is attached to troponin C

    • C.

      The detachment of myosin heads from actin needs binding of ATP.

    • D.

      The transverse tubules (T.T.) contains Ca voltage gated channels

    Correct Answer
    D. The transverse tubules (T.T.) contains Ca voltage gated channels
    Explanation
    The transverse tubules (T.T.) do not contain Ca voltage gated channels. These channels are actually located on the sarcoplasmic reticulum, which is a specialized type of smooth endoplasmic reticulum found in muscle cells. The Ca voltage gated channels on the sarcoplasmic reticulum are responsible for releasing Ca ions into the cytoplasm of the muscle cell, which then bind to troponin C and initiate muscle contraction. The transverse tubules, on the other hand, are invaginations of the cell membrane that help to propagate action potentials deep into the muscle cell, allowing for synchronous contraction of the entire muscle fiber.

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  • 2. 

    About the of skeletal muscles, all the following is true except:

    • A.

      Hypertrophy develops as a result of forced repeated contractions.

    • B.

      The function of the T system is the rapid transmission of the action potential from the cell -membrane to inside the muscle fibre

    • C.

      After the spike potential, the muscle excitability is abolished

    • D.

      Acetylcholine released at the M.E.P. is rapidly hydrolyzed by cholinesterase.

    Correct Answer
    C. After the spike potential, the muscle excitability is abolished
    Explanation
    After the spike potential, the muscle excitability is not abolished. In fact, after the spike potential, the muscle excitability is increased. This is due to the release of calcium ions from the sarcoplasmic reticulum, which triggers muscle contraction. Therefore, the statement "After the spike potential, the muscle excitability is abolished" is not true.

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  • 3. 

    Among the steps of skeletal muscle relaxation:

    • A.

      Inward spread of the depolarization wave along the transverse tubules.

    • B.

      Pumping of Ca back into the sarcoplasmic reticulum.

    • C.

      Release of Ca from the sarcoplasmic reticulum.

    • D.

      Binding of Ca to troponin C.

    Correct Answer
    B. Pumping of Ca back into the sarcoplasmic reticulum.
    Explanation
    During skeletal muscle relaxation, one of the steps involves the pumping of calcium (Ca) back into the sarcoplasmic reticulum. This process is essential for muscle relaxation as it helps to decrease the concentration of Ca in the cytoplasm. When the muscle is contracted, Ca is released from the sarcoplasmic reticulum, which allows for the binding of Ca to troponin C, leading to muscle contraction. However, during relaxation, the Ca needs to be removed from the cytoplasm to allow the muscle to return to its resting state. The pumping of Ca back into the sarcoplasmic reticulum helps to achieve this and allows for the muscle to relax.

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  • 4. 

    Concerning isometric and isotonic muscle contractions:

    • A.

      In isometric contraction, the elastic elements are not stretched.

    • B.

      During isometric contraction a load is moved and work is done.

    • C.

      During isotonic contraction most of the energy transformed into heat.

    • D.

      During isotonic contraction the muscle length is not changed.

    Correct Answer
    C. During isotonic contraction most of the energy transformed into heat.
    Explanation
    During isotonic muscle contraction, most of the energy is transformed into heat. Isotonic contraction refers to a type of muscle contraction where the muscle length changes while maintaining a constant tension. This type of contraction is responsible for movement and work done by the muscles. As the muscle contracts and shortens, it generates heat due to metabolic processes and energy expenditure. Therefore, during isotonic contraction, a significant amount of energy is converted into heat.

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  • 5. 

    In skeletal muscles:

    • A.

      The initiation of contraction occurs by binding of Ca to tropomyosin.

    • B.

      The action potential follows the work done.

    • C.

      The one way conduction at the M.E.P. is due to location of the chemical mediator (acetylcholine) in the nerve terminals.

    • D.

      Fatigue sets in after fatigue occurs in the nerves.

    Correct Answer
    C. The one way conduction at the M.E.P. is due to location of the chemical mediator (acetylcholine) in the nerve terminals.
    Explanation
    The correct answer states that the one-way conduction at the M.E.P. (motor end plate) is due to the location of the chemical mediator, acetylcholine, in the nerve terminals. This means that acetylcholine is released from the nerve terminals and binds to receptors on the motor end plate, triggering muscle contraction. This one-way conduction ensures that the signal travels in only one direction, from the nerve to the muscle, allowing for precise control of muscle movement.

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  • 6. 

    A series of stimuli that cause summation of contractions leads to:

    • A.

      Rigor.

    • B.

      Contracture.

    • C.

      Tonus.

    • D.

      Tetanus

    • E.

      Spasm.

    Correct Answer
    D. Tetanus
    Explanation
    When a series of stimuli causes summation of contractions, it leads to tetanus. Tetanus is a sustained contraction of a muscle due to a rapid succession of stimuli. In this state, the muscle remains contracted and does not relax. This can occur naturally during certain activities or can be artificially induced in medical procedures. It is different from contracture, which refers to a prolonged muscle contraction due to a lack of relaxation, and tonus, which is the normal level of tension in a muscle at rest. Rigor refers to a stiffening of muscles after death, and spasm is an involuntary and sudden contraction of a muscle.

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  • 7. 

    Regarding reaction of degeneration, which of the following is true:

    • A.

      There is increased muscle excitability

    • B.

      Skeletal muscle responds to both faradic and galvanic current

    • C.

      Skeletal muscle has longer chronaxie

    • D.

      ACC is lower than CCC

    Correct Answer
    C. Skeletal muscle has longer chronaxie
    Explanation
    The chronaxie is the minimum duration of an electrical stimulus required to elicit a response in a muscle or nerve. In the case of the reaction of degeneration, which occurs in damaged or denervated muscles, the muscle has a longer chronaxie. This means that it requires a longer duration of electrical stimulus to cause a contraction in the muscle. This is due to the loss of normal muscle innervation and the changes that occur in the muscle fibers as a result.

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  • Mar 14, 2023
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