Week 10 Quiz

In a sarcomere, one kind of filament is anchored to the Z discs and carries troponin and tropomyosin. Which protein makes that thin filament?

Select one.

• Myosin, the protein with heads
• Actin, with binding sites for the heads
• Collagen, the fiber protein of tendons and ligaments
• Keratin, the protein of the epidermis

ACh has triggered the muscle action potential, and the signal has run along the sarcolemma and down the T-tubules. Which event comes next?

Select one.

• Myosin heads attach to actin and pull
• ACh crosses the synaptic cleft
• The sarcoplasmic reticulum releases Ca²⁺
• Tropomyosin covers actin's binding sites

A motor neuron's signal reaches the neuromuscular junction. What does the motor neuron release across the synaptic cleft to the motor end-plate?

Select one.

• Acetylcholine (ACh)
• Calcium ions (Ca²⁺)
• ATP for the myosin heads
• Troponin for the thin filament

True or false: when a skeletal muscle fiber contracts, its actin and myosin filaments get shorter.

True or false.

• True
• False

Which description fits a motor unit?

Select one.

• One muscle fiber and all of its myofibrils
• A bundle of fibers wrapped by the perimysium
• The stretch of a myofibril between two Z discs
• One motor neuron plus every muscle fiber it supplies

Some hours after death, the body's muscles become stiff (rigor mortis). Which job of ATP has stopped, leaving the myosin heads locked?

Select one.

• Carrying the signal down the T-tubules
• Binding a myosin head to release it from actin
• Releasing ACh at the neuromuscular junction
• Binding troponin to uncover actin's sites

Select every step that uses ATP in a working skeletal muscle fiber.

Select every option that applies.

• The power stroke of an attached myosin head
• Releasing a myosin head from actin
• Pumping Ca²⁺ back into the sarcoplasmic reticulum
• Ca²⁺ binding to troponin
• ACh diffusing across the synaptic cleft

In an illustrative grip-fatigue series, five 10-second squeeze trials gave 24, 21, 18, 15, and 12 squeezes. What is the average number of squeezes per trial?

Select one.

• 15 squeezes per trial
• 22.5 squeezes per trial
• 18 squeezes per trial
• 12 squeezes per trial

The same illustrative grip-fatigue series fell from 24 squeezes in trial 1 to 12 squeezes in trial 5. What is the percent decline?

Select one.

• 50%
• 100%
• 12%
• About 67%

The muscles that keep a person sitting upright work for long periods without tiring. Which fiber type suits that job?

Select one.

• Fast glycolytic fibers, thick and glycogen-rich
• Fibers that contract quickly but tire fast
• Fibers with few mitochondria that store much glycogen for bursts
• Slow oxidative fibers, rich in mitochondria and myoglobin