Muscle Contraction

Muscle Contraction MDCAT MCQs with answers

19 past paper MCQs on Muscle Contraction, from the Support and Movement unit of MDCAT Biology. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.Which of the following is a muscle component that acts as a store of energy? (MDCAT 2022)

  1. ATP
  2. creatine phosphate
  3. myoglobin
  4. creatinine phosphate
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Correct answer: (b) creatine phosphate

Creatine phosphate hands its phosphate to ADP and so keeps ATP topped up during hard work.

2.During the sliding filament mechanism, ATP is used for: (MDCAT 2023)

  1. cross bridge formation
  2. cross bridge breaking
  3. dragging the filaments
  4. shortening of the filaments
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Correct answer: (b) cross bridge breaking

The head attaches and pulls without ATP; hydrolysing ATP is what releases it for the next stroke.

3.The accumulation of lactic acid in the muscles results in: (MDCAT 2024)

  1. extreme fatigue
  2. muscle contraction
  3. paralysis
  4. convulsion
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Correct answer: (a) extreme fatigue

Lactic acid builds up when the oxygen supply falls short, and the muscle tires.

4.Why thick filaments are unable to bind with thin filament in a relaxed muscle fiber? (UHS MDCAT 2025)

  1. Actin blocks the myosin binding site
  2. Tropomyosin blocks the myosin binding site
  3. Troponin blocks the myosin binding site
  4. Tropomyosin blocks the troponin binding site
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Correct answer: (b) Tropomyosin blocks the myosin binding site

Tropomyosin lies over the myosin binding sites of actin until calcium shifts it aside.

5.Once an action potential reaches the membrane of a skeletal muscle fiber, what is the first event that occurs in the contraction process? (UHS MDCAT 2025)

  1. Actin and myosin form a cross-bridge
  2. Calcium is pumped back into the sarcoplasmic reticulum
  3. Calcium is released from the sarcoplasmic reticulum
  4. ATP is hydrolyzed by troponin
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Correct answer: (c) Calcium is released from the sarcoplasmic reticulum

The action potential runs down the T tubules and the sarcoplasmic reticulum releases its calcium.

6.The primary role of calcium ions in muscle contraction is to: (KMU MDCAT 2025)

  1. Produce energy
  2. Bind with troponin
  3. Carry nerve impulses
  4. Breakdown ATP
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Correct answer: (b) Bind with troponin

Calcium binds troponin, which pulls the tropomyosin off the binding sites of actin.

7.The regulator of muscle contraction, which is released from sarcoplasmic reticulum is: (SIBA MDCAT 2025)

  1. Tropomyosin
  2. Troponin
  3. Calcium ions
  4. ATP
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Correct answer: (c) Calcium ions

Calcium is the ion released from the sarcoplasmic reticulum that lets the cross bridges form.

8.The event that occurs first during skeletal muscle contraction? (SZABMU MDCAT 2025)

  1. Cross-bridge formation
  2. Release of calcium from sarcoplasmic reticulum
  3. Power stroke
  4. Myosin head binds to ATP
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Correct answer: (b) Release of calcium from sarcoplasmic reticulum

The impulse first releases calcium from the sarcoplasmic reticulum; everything else follows from that.

9.What happens to calcium when skeletal muscles recover from contraction? (KMU MDCAT 2024)

  1. Released from the sarcoplasmic reticulum
  2. Released from the myosin head
  3. Pumped into the sarcoplasmic reticulum
  4. Exchanged for sodium ions
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Correct answer: (c) Pumped into the sarcoplasmic reticulum

Calcium pumps return it to the sarcoplasmic reticulum, and the fibre relaxes.

10.The muscle contraction involve the breakdown of cross bridges of active myosin filaments due to the following process: (SZABMU MDCAT 2023)

  1. ATP is oxidized
  2. ATP is reduced
  3. ATP is hydrolyzed
  4. ATP is synthesized
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Correct answer: (c) ATP is hydrolyzed

Splitting ATP on the myosin head is what breaks the cross bridge and cocks it again.

11.Tetany is caused by ________ in blood. (SZABMU MDCAT 2023)

  1. Low Ca++
  2. High Ca++
  3. Low Mg++
  4. High Mg++
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Correct answer: (a) Low Ca++

Too little calcium in the blood leaves the nerves over-excitable and the muscles in spasm.

12.Under activity of parathyroid glands causes a drop in blood of: (NUMS MDCAT 2023)

  1. Mg2+
  2. Na+
  3. K+
  4. Ca2+
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Correct answer: (d) Ca2+

Parathyroid hormone raises blood calcium, so too little of it lets the calcium fall.

13.During sliding of actin filaments, ATP is used for? (UHS MDCAT 2023)

  1. Cross bridge formation
  2. Cross bridge breaking
  3. Dragging filaments
  4. Shortening of filaments
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Correct answer: (a) Cross bridge formation

ATP is split on the myosin head, which cocks it ready to form the cross bridge.

14.Which event does not occur during muscle contraction: (NUMS MDCAT 2022)

  1. I-band shorten
  2. A-band shortens
  3. H-zone disappear
  4. Z-lines move closer
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Correct answer: (b) A-band shortens

The A band is the length of the thick filament, which does not change; the thin filaments slide past it.

15.Which of the following sections of a sarcomere does not shorten during contraction? (PMC Practice 2021)

  1. I band
  2. H zone
  3. A band
  4. None of these
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Correct answer: (c) A band

The A band is the length of the thick filament, which does not change as the thin ones slide in.

16.When a muscle fibre shortens, the following also shortens: (PMC Practice 2021)

  1. Actin filament
  2. Sarcomere
  3. Both Options A and B are correct
  4. Myosin
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Correct answer: (b) Sarcomere

The filaments keep their length; it is the sarcomere between the Z lines that shortens.

17.The function of calcium ions in muscle contraction is to: (UHS MDCAT 2019)

  1. polarize visible light
  2. Aid in the transmission of nerve impulse
  3. Bind to troponin molecule and cause them to move
  4. Bind to tropomyosin molecule and cause them to form cross bridges
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Correct answer: (c) Bind to troponin molecule and cause them to move

Calcium binds troponin, which shifts the tropomyosin off the binding sites of actin.

18.According to sliding filament theory, when muscle fibers are stimulated by nervous system, which of the following changes occurs? (UHS MDCAT 2015)

  1. I-bands shorten
  2. H-zone becomes more visible
  3. Z-lines move further apart
  4. A-bands shorten
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Correct answer: (a) I-bands shorten

The thin filaments slide in, so the I band and the H zone narrow while the A band holds its length.

19.If lactic acid build up in thigh muscles, it causes muscle tiredness and pain. This condition is called: (UHS MDCAT 2015)

  1. Muscle Fatigue
  2. Tetany
  3. Cramps
  4. Oxygen debt in muscles
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Correct answer: (a) Muscle Fatigue

Lactic acid built up in a working muscle brings on muscle fatigue.

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