Chapter 10 Section 4

In response to action potentials arriving along the transverse tubules, the sarcoplasmic reticulum releases

• acetylcholine

• sodium ions

• potassium ions

• calcium ions

• hydrogen ions

Each skeletal muscle fiber is controlled by a motor neuron at a single

• synaptic knob

• sarcomere

• neuromuscular junction

• synaptic cleft

• transverse tubule

The narrow space between the synaptic terminal and the muscle fiber is the

• synaptic knob

• motor end plate

• motor unit

• synaptic cleft

• M line

Which of the following become connected by myosin cross-bridges during muscle contraction?

• thin filaments and thick filaments

• thick filaments and titin filaments

• z disks and actin filaments

• thick filaments and t-tubules

• thin filaments and t-tubules

After death, muscle fibers run out of ATP and calcium begins to leak from the sarcoplasmic reticulum into the sarcoplasm. This results in a condition known as

• tetany

• treppe

• depolarization

• rigor mortis

• oxygen debt

In rigor mortis

• the myosin heads are attached to actin.

• ATP is depleted.

• calcium ions keep binding to troponin.

• sustained contractions occur.

• All of the answers are correct.

In a sarcomere, cross-bridge attachment occurs specifically in the

• zone of overlap

• A band

• I band

• M line

• H band

Triggering of the muscle action potential occurs after

• acetylcholine binds to chemically-gated channels in the motor end plate.

• acetylcholinesterase is released from synaptic vesicles into the synaptic cleft.

• calcium ion binds to channels on the motor end plate.

• the action potential jumps across the neuromuscular junction.

• Any of these can produce an action potential in the muscle cell.

The following is a list of the events that occur during a muscle contraction. What is the correct sequence of these events?

1. Myosin cross-bridges bind to the actin.

2. The free myosin head splits ATP.

3. Calcium ion is released from the sarcoplasmic reticulum.

4. The myosin head pivots toward the center of the sarcomere.

5. Calcium ion binds to troponin.

6. The myosin head binds an ATP molecule and detaches from the actin.

• 1, 3, 5, 4, 6, 2

• 5, 1, 4, 6, 2, 3

• 3, 5, 1, 2, 4, 6

• 3, 5, 1, 4, 6, 2

• 1, 4, 6, 2, 3, 5

How would the loss of acetylcholinesterase from the motor end plate affect skeletal muscle?

• It would make the muscles less excitable.

• It would produce muscle weakness.

• It would cause muscles to stay contracted.

• It would cause muscles to stay relaxed.

• It would have little effect on skeletal muscles.