Week 10 — Quiz (auto-graded) · Muscle Tissue & the Physiology of Contraction

Course: Anatomy & Physiology I (BIOL 2301 + BIOL 2101) · Silver Oak University (fictional sample) · Prof. Navarro
Objective tested: Objective 5 — skeletal-muscle structure (the sarcomere); the sliding-filament model; the steps of contraction in order; the neuromuscular junction, ACh, calcium, troponin/tropomyosin, and ATP.
Points: 10 (1 each) · Assignment group: Quizzes (10% of grade) · Due: end of Module 10.

This is the human-readable quiz with its vetted answer key and feedback. The import-ready Classic QTI is in F-quiz-week-10-qti.xml (generated by the shared validated script — parses with 10 items, every single-answer item exactly one correct). The reusable item-bank entries and the Canvas placement block are at the bottom of this file.

Blueprint

No trick questions; distractors target the Week 10 misconceptions named in the lecture outline (actin/myosin swap, step order, NMJ vs. SR, slide vs. shrink, ATP for contraction and relaxation).

Questions, key, and feedback

Q1 (MC). Within a skeletal muscle fiber, what is the sarcomere?
- A. The plasma membrane of the muscle fiber
- B. The basic contractile (functional) unit of the muscle fiber, running from one Z disc to the next ✅
- C. A bundle of muscle fibers wrapped in connective tissue
- D. The calcium-storage organelle of the muscle cell
Feedback: The sarcomere (Z disc to Z disc) is the basic contractile unit — many in a row form a myofibril. (A is the sarcolemma; C is a fascicle; D is the sarcoplasmic reticulum.)

Q2 (MC). In the sarcomere, which statement correctly pairs the two filament proteins with their thickness?
- A. Actin is the thick filament; myosin is the thin filament
- B. Actin is the thin filament; myosin is the thick filament ✅
- C. Both actin and myosin are thick filaments
- D. Troponin is the thick filament; tropomyosin is the thin filament
Feedback: Actin = thin; myosin = thick — and the pulling heads (cross-bridges) belong to myosin. The classic flip is calling actin "thick"; the hook is "actin is thin." (Troponin and tropomyosin are regulatory proteins, not the filaments themselves.)

Q3 (Matching — put the steps in order). Put the steps of skeletal-muscle contraction in the correct ORDER (Step 1 = FIRST through Step 5 = LAST).
| Position | Correct step |
|---|---|
| Step 1 (FIRST) | A motor-neuron action potential reaches the NMJ and releases acetylcholine (ACh) |
| Step 2 (SECOND) | ACh triggers an action potential along the muscle fiber (sarcolemma) and down the T-tubules |
| Step 3 (THIRD) | Calcium (Ca²⁺) is released from the sarcoplasmic reticulum |
| Step 4 (FOURTH) | Ca²⁺ binds troponin, moving tropomyosin off actin's binding sites |
| Step 5 (LAST) | Myosin heads form cross-bridges and pull actin (the power stroke, using ATP) so the filaments slide |
Feedback: The order is ACh → muscle action potential → calcium → troponin/tropomyosin → cross-bridge. The two errors to avoid: starting with calcium (the nerve signal comes first, and causes the calcium release) and skipping the NMJ/ACh handoff. The signal-to-calcium link is excitation–contraction coupling.

Q4 (MC). According to the sliding-filament model, how does a sarcomere shorten during contraction?
- A. The actin and myosin filaments each get physically shorter
- B. The thin (actin) filaments slide past the thick (myosin) filaments toward the center, so the Z discs are pulled closer together ✅
- C. The Z discs dissolve and re-form farther apart
- D. The myosin filaments break apart into actin
Feedback: The filaments slide and overlap more — their lengths never change; the Z discs are drawn closer, so the sarcomere shortens. "Slide, don't shrink." (The A band, the thick-filament length, stays constant — the fingerprint of sliding.)

Q5 (MC). Which neurotransmitter does the motor neuron release at the neuromuscular junction (NMJ) to signal a skeletal muscle fiber?
- A. Dopamine
- B. Acetylcholine (ACh) ✅
- C. Insulin
- D. Adenosine triphosphate (ATP)
Feedback: The motor neuron releases acetylcholine (ACh) into the synaptic cleft; ACh binds the motor end-plate and sparks the muscle's own action potential. (Insulin is a hormone; ATP is the energy currency, not the signal across the cleft.)

Q6 (MC). During excitation–contraction coupling, where does the calcium (Ca²⁺) that triggers contraction come from?
- A. The mitochondria
- B. The sarcoplasmic reticulum (SR) ✅
- C. The blood plasma directly through the sarcolemma
- D. The Z discs
Feedback: The SR stores and releases the Ca²⁺. When the muscle's action potential reaches it (via the T-tubules), the SR dumps calcium into the sarcoplasm. Don't confuse this with the NMJ, which releases ACh — different molecule, different source.

Q7 (MC). What is the role of troponin and tropomyosin in muscle contraction?
- A. They form the thick filament that pulls on actin
- B. At rest, tropomyosin covers the binding sites on actin; when Ca²⁺ binds troponin, tropomyosin shifts away to EXPOSE those binding sites ✅
- C. They are the enzymes that make ATP for the power stroke
- D. They store the calcium that triggers contraction
Feedback: Tropomyosin is the strand that covers actin's binding sites; troponin is the protein that binds calcium and pulls tropomyosin off, exposing the sites so myosin can form cross-bridges. Calcium = trigger, troponin = receiver, tropomyosin = gate.

Q8 (True / False). "During a muscle contraction, the actin and myosin filaments themselves shorten."
- True
- False ✅
Feedback: False. The filaments do not shorten — they slide past each other and overlap more, pulling the Z discs closer so the sarcomere shortens. Their lengths stay the same throughout (sliding-filament model).

Q9 (Multiple answer — select all that apply). Which of the following are directly required for a normal skeletal-muscle contraction?
- A. Acetylcholine (ACh) at the neuromuscular junction ✅
- B. Calcium ions (Ca²⁺) released from the sarcoplasmic reticulum ✅
- C. ATP to power the cross-bridge cycle ✅
- D. Bile from the gallbladder
- E. Insulin from the pancreas
Feedback: Contraction requires ACh (the NMJ signal), Ca²⁺ (to uncover the binding sites), and ATP (to power the power stroke and the head's detachment). Bile (fat digestion) and insulin (blood-glucose control) have nothing to do with the contraction machinery — they're the distractors.

Q10 (MC). A muscle fiber packed with many mitochondria and a rich blood supply is best suited to:
- A. Brief, all-out bursts of power that fatigue almost immediately
- B. Sustained, fatigue-resistant activity such as maintaining posture, because abundant mitochondria keep making ATP aerobically ✅
- C. Storing calcium for the whole muscle
- D. Conducting the nerve signal faster than a motor neuron
Feedback: Structure → function: many mitochondria + good blood supply = steady aerobic ATP = fatigue-resistant fibers (good for posture and endurance). Fibers built for short, powerful bursts rely on quick anaerobic ATP and tire fast. (Calcium storage is the SR's job; nerve conduction is the neuron's.)

Answer key (quick reference)

Quality gate (self-checked): each single-answer item has exactly one correct option; the multiple-answer item (Q9) requires all three of ACh / Ca²⁺ / ATP and requires the bile and insulin distractors to be left unselected; the sequence-via-matching item (Q3) maps five steps to five ordered positions, verified against standard physiology (OpenStax §10.2–10.3: motor-neuron AP → ACh at the NMJ → muscle AP/T-tubules → Ca²⁺ from the SR → Ca²⁺ binds troponin / tropomyosin shifts → cross-bridge/power stroke needing ATP). Sarcomere structure (actin = thin, myosin = thick, Z-disc boundaries), the sliding-filament mechanism (filaments slide/overlap, do not shorten — Q8 keyed False), the NMJ neurotransmitter (ACh, Q5), and the calcium source (the SR, Q6) are each verified. Anatomy-accuracy gate: PASS. No computation in this quiz, so no arithmetic to mis-key — this is a process-ordering week; the quiz's "ordered process" item (Q3) is the load-bearing check, and the quantitative gate does not apply to this quiz (the Week 10 lab carries the only numbers — grip-fatigue averages, re-verified in /tmp Python).

Item-bank entries (for variants + the midterm/final)

All ten items are tagged course=BIOL2301 · week=10 · objective=5 · topic=muscle-structure-and-contraction and deposited in Item Bank: Week 10 — Muscle Tissue & Contraction. The final (Week 16) and the per-term variant updates draw fresh items from this bank, including the sequence/ordering item for the cumulative "order a process" requirement. (Tags: q1 sarcomere-unit, q2 actin-thin-myosin-thick, q3 contraction-steps-order, q4 sliding-filament, q5 nmj-ach, q6 calcium-sr, q7 troponin-tropomyosin, q8 filaments-shorten-misconception, q9 required-for-contraction, q10 structure-function-fatigue.)

Canvas placement block

canvas_object   = Quizzes::Quiz
title           = "Week 10 Quiz — Muscle Tissue & the Physiology of Contraction"
assignment_group = "Quizzes"
points_possible = 10
grading_type    = points
due_offset_days = 6        # 6 days after module start
published       = true
shuffle_answers = true     # NOTE: the ordering item (Q3) maps positions to steps; shuffling answer choices is safe, the position labels stay fixed
provenance      = "~ Prof. Navarro's edition · Fall 2026 · built with thecoursemaker.com"