Question

1. When an action potential reaches the T-tubule, it will activate the dihydropyridine receptor at the T-tubule to change conformational shape. Dihydropyridine receptor will trigger ryanodine receptor channel to secrete Ca²⁺ from the sarcoplasmic reticulum into the cytosol. When action potential is absent, Ca²⁺ ATPase at the sarcoplasmic reticulum will pump cytosolic Ca²⁺ into the sarcoplasmic reticulum.

Select one:

a. True

b. False

2. What is TRUE about the myofibril?

Select one:

a. The thick and thin filaments on the myofibril are arranged in sarcomere, which causes the striation on the muscle fiber and also is the functional unit of the cell.

b. The thick filament is made of multiple myosin. Each myosin is a contractile protein made of two tails and two heads, also known as crossbridge.

c. Nebulin is an inelastic accessory protein that anchors the thin filament made of multiple contractile proteins called actin and regulatory proteins called troponin and tropomyosin.

d. During muscle contraction, the A-band does not shorten but sarcomere shortens due to shortening of the I-band and H-zone.

e. All of the above

f. None of the above

3. What characterizes muscle contraction?

Select one:

a. When Ca2+ binds to troponin, tropomyosin will slide and exposes the actin binding site on actin.

b. ATP will power the myosin head to bind to actin and begin the power stroke.

c. The ADP is released from the myosin head in the middle of the power stroke, then Pi is released at the end of the power stroke.

d. ATP binds at the myosin ATPase to unbind myosin from actin.

e. If ATP remains bound at the myosin ATPase, it will prevent the myosin from unbinding to actin, known as rigor mortis.

f. The power stroke will cause the sliding of the thick filament closer to the M-line.

4. Withdrawal reflex and crossed extensor reflex are types of polysynaptic reflexes while stretch reflex that involves muscle spindle is a monosynaptic reflex.

Select one:

a. True

b. False

5. What characterizes the motor-end-plate of the muscle fiber?

Select one:

a. Highly folded region of the sarcolemma

b. High concentration of nicotinic receptors

c. Contains acetylcholine esterase that hydrolyzes acetylcholine into acetyl and choline

d. Synapses to the axon terminal of the somatic motor neuron

e. All of the above

f. None of the above

Answer 1

1) Answer : True

Acetylcholine is released from the axon terminal of the neutron and it binds to dihydropyridine receptor in the T- tubule of sacrolemma. Action potential travels down the T- tubule and it triggers ryanodine receptor in the sacroplamic reticulum to release calcium into sacroplasm. Calcium binds troponin to form cross bridge between actin and myosin and it leads to muscle contraction. When action potential is absent, ATPase pump calcium back into the sacroplasmic reticulum. And, acetylcholine is removed by acetylcholinesterase. Finally, muscle relaxation occurs.