Human A&PBIO 304 · American River College ← Week 04 pre-work

BIO 304 · Week 04 · Interactive Workbook

Sliding Filament & the Cross-Bridge Cycle

Type your answers, draw in the boxes or upload a photo of your hand drawing, then use Save as PDF to submit. Your work saves on this device as you go.

Paste attempts0

Your work autosaves on this device.

Open the full notes →

Part 1 of 4 · Recall

Fill in the blanks

Type the term that completes each statement, using the word bank. Pull it from memory first.

Word bank

Tropomyosin shiftsCa²⁺ releaseTropomyosin re-covers actinSarcomere returns to restACh releaseA band stays the same2. Power strokeEnd-plate potential3. Cross-bridge detachmentAction potential stopsAction potential along sarcolemmaAction potential arrives at axon terminalCross-bridge can now formPermanent cross-bridgesThin filaments slide

  1. depolarizes the motor neuron ending
  2. voltage-gated Ca²⁺ opens; vesicles fuse; acetylcholine into synapse
  3. Na+ enters; sarcolemma depolarizes to threshold
  4. and down the T-tubules
  5. SR floods cytoplasm with Ca²⁺
  6. unblocks the myosin-binding site on actin
  7. myosin head reaches actin
  8. head pivots; thin filament slides toward M line; ADP + Pi released
  9. new ATP binds myosin head; head releases actin
  10. toward the M line on both sides
  11. thick filament length does not change
  12. no more depolarization
  13. no more binding sites
  14. thin filaments slide back
  15. muscles stay locked

Define it: high-yield vocabulary

Write a clear definition in your own words for each term.

  1. Cross-bridge
  2. Power stroke
  3. Troponin
  4. Tropomyosin
  5. Sliding filament theory
  6. SERCA pump
  7. Acetylcholine
  8. End-plate potential
  9. Calcium (role in contraction)
  10. Rigor mortis

Part 2 of 4 · Anatomy lab

Draw and label

Box A. The 4-step cross-bridge cycle

Directions

  1. Draw a large square that fills the box.
  2. Top-left corner: COCKING. Draw a myosin head in its high-energy, cocked position. Label it. Note that ATP has just been hydrolyzed to ADP plus Pi, both still bound to myosin.
  3. Top-right corner: BINDING. Draw the myosin head attached to actin. Note that calcium has bound troponin and tropomyosin has shifted to expose the actin binding site.
  4. Bottom-right corner: POWER STROKE. Draw the myosin head pivoted, pulling actin toward the M line. Note that ADP and Pi are released.
  5. Bottom-left corner: DETACHMENT. Draw the myosin head with a NEW ATP bound, released from actin. Note that ATP binding is required for detachment.
  6. Connect the corners with clockwise arrows. Mark every step where ATP is consumed or required.
Color Size Tool
Your uploaded drawing for Box A. The 4-step cross-bridge cycle

Box B. Calcium release and reuptake

Directions

  1. Draw the sarcolemma at the top of the box, with an action potential arriving (use a small arrow).
  2. Draw a T-tubule diving down from the sarcolemma into the cell.
  3. Draw the sarcoplasmic reticulum wrapping a myofibril below.
  4. Add arrows showing Ca-squared-plus flowing OUT of the SR into the cytoplasm during stimulation.
  5. Draw a second small panel beside this one labeled Relaxation. Show the SR Ca-squared-plus ATPase pumping calcium BACK into the SR.
  6. Label every structure: Sarcolemma, T-tubule, Sarcoplasmic reticulum, Triad, SR calcium ATPase.
Color Size Tool
Your uploaded drawing for Box B. Calcium release and reuptake

Structures to label

Label each on your drawing.

  1. Myosin head (cocked)
  2. Myosin head (bound)
  3. Myosin head (post power stroke)
  4. Actin binding site
  5. Troponin
  6. Tropomyosin
  7. Calcium (Ca2+)
  8. ATP
  9. ADP + Pi
  10. Power stroke arrow
  11. Sarcolemma
  12. T-tubule
  13. Sarcoplasmic reticulum
  14. Triad
  15. SR Ca2+ ATPase

Part 3 of 4 · Physiology lab

Reason it through

A. Sequencing puzzle: from nerve to power stroke

Explain the main structure-function relationship for this topic.

B. Synthesis

1. Rigor mortis sets in hours after death. Explain the molecular mechanism using your cycle drawing. Which step cannot proceed, and why?
2. Curare blocks the nicotinic acetylcholine receptor at the neuromuscular junction. At which step does the entire chain stall, and what is the patient's clinical picture?
3. Malignant hyperthermia is caused by a mutation that makes the SR calcium release channel hyperactive in response to certain anesthetics. Walk through the cycle and explain why body temperature climbs so rapidly.

Submit

Save as PDF, then upload to Canvas.

The exported PDF stamps your name and paste-attempt count. Drawn-here or hand-drawn diagrams only; typed or AI-generated diagrams are not accepted.

Submit on Canvas →