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

BIO 304 · Week 04 · Interactive Workbook

Muscle Physiology

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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

Acetylcholine Motor end plate Calcium Troponin Tropomyosin Power stroke ATP SERCA Motor unit Tetanus Type I Type IIx

  1. The neurotransmitter released by the motor neuron at the neuromuscular junction.
  2. The folded region of sarcolemma packed with ACh receptors.
  3. The ion the sarcoplasmic reticulum releases to trigger contraction.
  4. The thin-filament protein that calcium binds to.
  5. The protein that physically blocks the actin binding sites at rest.
  6. The step where the myosin head pivots and pulls the thin filament inward.
  7. The molecule that binds myosin so the head can release from actin.
  8. The pump that pulls calcium back into the SR during relaxation.
  9. One motor neuron plus all the muscle fibers it controls.
  10. Stimulation so rapid the muscle never relaxes, producing smooth maximal force.
  11. Red, fatigue-resistant, aerobic fiber built for endurance.
  12. White, anaerobic fiber that is powerful but fatigues quickly.

Define it: high-yield vocabulary

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

  1. Acetylcholine
  2. Acetylcholinesterase
  3. T-tubule
  4. Troponin
  5. Tropomyosin
  6. Cross-bridge
  7. Power stroke
  8. SERCA
  9. Motor unit
  10. Size principle
  11. Tetanus
  12. Creatine phosphate

Part 2 of 4 · Anatomy lab

Draw and label

Box A. Neuromuscular junction

Directions

  1. Draw the swollen end of a motor neuron axon. Label it Axon terminal.
  2. Inside it draw several small circles. Label them ACh vesicles.
  3. Draw the narrow gap below the terminal. Label it Synaptic cleft.
  4. Draw the folded muscle membrane below the gap. Label it Motor end plate.
  5. Add receptor shapes on the folds. Label them ACh receptors.
  6. Draw an arrow showing Na+ entering the muscle. Label it.
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Your uploaded drawing for Box A. Neuromuscular junction

Box B. Cross-bridge cycle (four steps)

Directions

  1. Draw a thick filament (myosin) with one head below a thin filament (actin). Make four small panels.
  2. Panel 1: head attached to actin. Label 1 Cross-bridge forms.
  3. Panel 2: head pivoted, thin filament pulled inward. Label 2 Power stroke.
  4. Panel 3: a new ATP binds and the head releases. Label 3 Detach (ATP).
  5. Panel 4: ATP splits and the head re-cocks. Label 4 Re-cock (ADP + Pi).
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Your uploaded drawing for Box B. Cross-bridge cycle (four steps)

Structures to label

Label each on your drawing.

  1. Axon terminal
  2. Synaptic cleft
  3. Motor end plate
  4. ACh receptor
  5. T-tubule
  6. Sarcoplasmic reticulum
  7. Calcium
  8. Troponin
  9. Tropomyosin
  10. Myosin head
  11. Actin binding site
  12. Power stroke

Part 3 of 4 · Physiology lab

Reason it through

A. Mechanism trace

Trace the full pathway from a motor neuron action potential to a single power stroke. Name every structure the signal passes through in order: axon terminal, ACh, receptors, sarcolemma, T-tubule, SR, calcium, troponin, tropomyosin, and the myosin head.

B. Synthesis

1. In myasthenia gravis, antibodies destroy ACh receptors on the motor end plate. Predict the effect on muscle strength and explain why symptoms get worse with repeated use.
2. An organophosphate pesticide blocks acetylcholinesterase. Predict what happens at the neuromuscular junction and to the muscle, and explain which step fails.
3. Eccentric (lengthening) contractions, like lowering a heavy weight slowly, cause the most muscle soreness. Explain what is happening to the sarcomeres and why.

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