Mastering Muscles

Question 1

What is the role of calcium in the cross bridge cycle?

Answer 1

Calcium binds to troponin, altering its shape

Question 2

What role does tropomyosin play in the cross bridge cycle?

Answer 2

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.

Question 3

How does troponin facilitate cross bridge formation?

Answer 3

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

Question 4

What, specifically, is a cross bridge?

Answer 4

myosin binding to actin

Question 5

Which event causes cross bridge detachment?

Answer 5

ATP binding to the myosin head

Question 6

Where in the cross bridge cycle does ATP hydrolysis occur?

Answer 6

during the cocking of the myosin head

Question 7

How/when does the myosin head cock back to store energy for the next cycle?

Answer 7

After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.

Question 8

BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle?

Answer 8

Myosin heads would remain detached, unable to cock.

Question 9

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?

Answer 9

There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.

Question 10

What is the type of chemical reaction used to rebuild ADP into ATP?

Answer 10

dehydration synthesis

Question 11

Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?

Answer 11

glycolysis

Question 12

Which of the following processes produces 36 ATP?

Answer 12

Krebs cycle and oxidative phosphorylation

Question 13

The “rest and recovery” period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________.

Answer 13

Pyruvic acid is converted back to lactic acid.

Question 14

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?

Answer 14

white fast twitch fibers

Question 15

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?

Answer 15

acetylcholine (ACh)

Question 16

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?

Answer 16

voltage-gated calcium channels

Question 17

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?

Answer 17

exocytosis

Question 18

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?

Answer 18

Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.

Question 19

How is acetylcholine (ACh) removed from the synaptic cleft?

Answer 19

simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)

Question 20

The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?

Answer 20

terminal cisterns (cisternae) of the sarcoplasmic reticulum

Question 21

Which of the following statements best describes the pathology associated with periodic paralysis?

Answer 21

Skeletal muscles are plagued by being flaccid for short periods.

Question 22

What are the ions directly associated with all forms of periodic paralysis due to the fact that the channels for these ions are defective?

Answer 22

sodium and calcium

Question 23

How does the permanent depolarization of the skeletal muscle result in a flaccid (non-contracted) paralysis?

Answer 23

The muscle cell would not be able to depolarize a second time because the voltage-gated sodium channel never inactivates.

Question 24

There are several hypotheses about the causes of muscular fatigue. These include depleted muscle glycogen stores, ion imbalances (especially K+), and which other mechanism?

Answer 24

Elevated Pi interfering with Ca2+ release