StudyStore

Free MCAT-style practice, 3B

MCAT Muscle Contraction Practice Questions: Sliding Filament and Muscle Types

By StudyStore · Published 2026-11-04 · 8 original questions · about 12 min

Eight free MCAT-style practice questions on the sliding filament model, calcium and troponin, the sarcomere, ATP use and differences among skeletal, cardiac and smooth muscle, with explanations.

Email me free MCAT notes, practice sets and new packs from StudyStore. Double opt-in, unsubscribe in one click. Privacy

Quick concept primer

Skeletal muscle contracts through the sliding filament model. In a sarcomere, thin filaments (actin with troponin and tropomyosin) slide past thick filaments (myosin), pulled by cross bridges. The sarcomere shortens, so the I band and H zone shrink while the A band (the length of thick filaments) stays constant, and the distance between Z lines falls.

An action potential reaches the muscle through the neuromuscular junction (acetylcholine on nicotinic receptors), spreads down T tubules and releases Ca2+ from the sarcoplasmic reticulum. Ca2+ binds troponin C, moving tropomyosin off the myosin binding sites on actin. Myosin heads bound to ADP and Pi make a power stroke; ATP binding detaches the head, and ATP hydrolysis re-cocks it. Rigor mortis occurs when ATP runs out and heads stay attached. Cardiac muscle is striated, has gap junctions and is involuntary; smooth muscle lacks sarcomeres and is regulated by calmodulin and myosin light chain kinase.

8 practice questions

Try each question before opening the explanation. Click "Show answer and explanation" to check yourself. All questions are original and written for study practice.

Question 1

During contraction of a skeletal muscle sarcomere, which band remains the same length?

  1. I band
  2. H zone
  3. A band
  4. The distance between adjacent Z lines
Show answer and explanation

Answer: C. A band

The A band corresponds to the length of the thick filaments, which do not change length as filaments slide. The I band and H zone shrink as thin filaments move toward the center, and the Z lines move closer together.

Question 2

Which event directly allows myosin heads to bind actin in skeletal muscle?

  1. Calcium binds troponin, causing tropomyosin to move off the binding sites on actin
  2. Sodium binds tropomyosin
  3. ATP binds to actin
  4. Calcium binds myosin directly
Show answer and explanation

Answer: A. Calcium binds troponin, causing tropomyosin to move off the binding sites on actin

Calcium released from the sarcoplasmic reticulum binds troponin C and shifts tropomyosin, exposing myosin binding sites on actin. Without calcium, tropomyosin blocks the sites even if myosin heads are ready.

Question 3

What is the role of ATP binding to a myosin head during the cross bridge cycle?

  1. It causes the power stroke
  2. It causes the myosin head to detach from actin
  3. It makes calcium enter the cell
  4. It phosphorylates tropomyosin
Show answer and explanation

Answer: B. It causes the myosin head to detach from actin

The power stroke follows release of ADP and Pi. A new ATP molecule then binds the myosin head and lowers its affinity for actin, so the head detaches. Hydrolysis of ATP re-cocks the head so another cycle can start.

Question 4

Rigor mortis develops after death because

  1. calcium levels in the cytosol fall
  2. acetylcholine is released continuously
  3. tropomyosin permanently covers the binding sites
  4. there is no ATP to detach myosin heads from actin
Show answer and explanation

Answer: D. there is no ATP to detach myosin heads from actin

Without ATP, myosin heads remain bound to actin in a rigid state. Ca2+ also leaks into the cytoplasm after death, which keeps binding sites exposed. The stiffness ends later as proteins degrade.

Question 5

Which structure stores the calcium that is released to trigger skeletal muscle contraction?

  1. T tubule
  2. Sarcoplasmic reticulum
  3. Mitochondrion
  4. Golgi apparatus
Show answer and explanation

Answer: B. Sarcoplasmic reticulum

The sarcoplasmic reticulum is a specialized smooth endoplasmic reticulum that stores Ca2+. T tubules carry the action potential into the fiber, where it triggers Ca2+ release from the nearby sarcoplasmic reticulum.

Question 6

Which of the following is a characteristic of smooth muscle but not skeletal muscle?

  1. Calcium binds calmodulin, which activates myosin light chain kinase
  2. Regulation through troponin
  3. Striations from organized sarcomeres
  4. Voluntary control by somatic neurons
Show answer and explanation

Answer: A. Calcium binds calmodulin, which activates myosin light chain kinase

Smooth muscle has no troponin. Calcium binds calmodulin, which activates myosin light chain kinase to phosphorylate myosin and start cross bridge cycling. It is not striated and is controlled by the autonomic nervous system, hormones and local factors.

Question 7

Cardiac muscle cells contract in a coordinated way because they are connected by

  1. neuromuscular junctions
  2. tight junctions that block ion flow
  3. gap junctions in the intercalated discs
  4. plasmodesmata
Show answer and explanation

Answer: C. gap junctions in the intercalated discs

Intercalated discs contain desmosomes for mechanical strength and gap junctions that allow ions to spread electrical activity from cell to cell, so the myocardium acts as a functional syncytium. Plasmodesmata are found in plants.

Question 8

A motor neuron releases acetylcholine at the neuromuscular junction. Which sequence correctly follows?

  1. Muscle action potential, T tubule depolarization, Ca2+ release, contraction
  2. Ca2+ release, muscle action potential, T tubule depolarization, contraction
  3. Contraction, Ca2+ release, muscle action potential, T tubule depolarization
  4. T tubule depolarization, contraction, muscle action potential, Ca2+ release
Show answer and explanation

Answer: A. Muscle action potential, T tubule depolarization, Ca2+ release, contraction

ACh binds nicotinic receptors on the motor end plate, depolarizing the muscle membrane. The action potential spreads into T tubules, which signal the sarcoplasmic reticulum to release Ca2+, and calcium then initiates cross bridge cycling.

Free MCAT sampler

Free sample: MCAT cheat sheet (PDF)

Join the list and download a free sample from a paid pack: the 3-page Amino Acids, Proteins and Enzymes cheat sheet (PDF). We also email free MCAT notes and practice sets.

Free sampler, no signup needed: 51 study notes with original diagrams and 5-question quizzes, 80 practice sets (706 questions with full explanations) and the 2027 study schedule generator.

Email me free MCAT notes, practice sets and new packs from StudyStore. Double opt-in, unsubscribe in one click. Privacy

Keep practicing

Written by StudyStore from standard scientific facts as a study aid. These are not official exam questions and are not affiliated with or endorsed by any testing organization. Always check values against the reference provided with your exam or course.

Spotted a mistake in a question? Report a problem or suggest something