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Human A&P BIO 304 · American River College ← Course home (Week 4)

BIO 304 . WEEK 4 . MONDAY . LAB WORKBOOK

Skeletal Muscle Microanatomy

From whole muscle down to the sarcomere: the structural ladder of contractile tissue.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

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Part 1 of 2

Anatomy Lab

1A. What you will draw

Today you will draw the muscle hierarchy from the outside in, then a single sarcomere in detail. Use two boxes below. Box A is for the hierarchy. Box B is for the sarcomere close-up. Sketch, do not trace.

Box A. Hierarchy (whole muscle to myofibril)

Directions

  1. Draw a long oval representing a whole muscle (cross-section). Wrap it in a thin line. Label that line Epimysium.
  2. Inside the oval, draw three or four smaller circles. Each is a fascicle. Wrap one of them with a thin line. Label that line Perimysium.
  3. Inside one fascicle, draw several smaller circles. Each is a muscle fiber (cell). Wrap one with a thin line. Label that line Endomysium.
  4. Inside one muscle fiber, draw a stack of long rods. Each rod is a myofibril. Label one Myofibril.
  5. Above your hierarchy, write the order of wrappings from outside to inside in one short sentence.

Box B. Sarcomere close-up

Directions

  1. Draw a long rectangle. Mark the left and right ends with vertical lines. Label both lines Z line.
  2. In the center, draw a vertical line. Label it M line.
  3. Between the two Z lines, draw thick filaments (myosin) in the middle and thin filaments (actin) extending from each Z line.
  4. Bracket and label the A band (the full length of the thick filaments).
  5. Bracket and label the I band (the region with only thin filaments).
  6. Bracket and label the H zone (the central thick-only region).
  7. Draw a T-tubule entering from above and a sarcoplasmic reticulum wrapping the myofibril. Label both.

1C. Structures to label (15)

After you finish each drawing, label every structure below directly on your sketch.

  1. Epimysium
  2. Perimysium
  3. Endomysium
  4. Muscle fiber (cell)
  5. Myofibril
  6. Sarcomere
  7. Z line
  8. M line
  9. A band
  10. I band
  11. H zone
  12. Thick filament (myosin)
  13. Thin filament (actin)
  14. T-tubule
  15. Sarcoplasmic reticulum

Part 2 of 2

Physiology Lab

2A. Mechanism trace: from action potential to power stroke

An action potential has just arrived at the sarcolemma of a muscle fiber. List the next 8 events that lead to a single power stroke. For each event, name WHERE it happens (which structure), WHAT moves (ion or molecule), and what changes STRUCTURALLY at the sarcomere.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. The I band shortens dramatically during contraction, but the A band barely changes length. Explain why, in terms of which filaments make up each band.
2. A toxin disrupts the triad junctions specifically (the points where T-tubules meet the SR). Predict the effect on contraction and explain at which step the cycle fails.
3. A muscle is stretched so far that thick and thin filaments no longer overlap. Predict the tension the muscle can generate at this length, and justify your answer using the cross-bridge mechanism.

3. What to submit

Complete both the Anatomy Lab (your own drawings, hand-labeled, plus the structures list) and the Physiology Lab (activity and synthesis questions). Photograph or scan every page and upload to Canvas before the deadline listed on the schedule. Hand-drawn, hand-labeled work is the integrity mechanism for this course. Typed or AI-generated diagrams are not accepted.