Question 1

Which of the following correctly lists the structures of muscle tissue in order from largest to smallest?

Accepted Answer

Muscle, muscle fiber, myofibril, myofilament

Question 2

Which of the following best describes the role of calcium ions ($$\mathrm{Ca$$^{2+}$$}) in $$muscle contraction?

Accepted Answer

They bind to troponin, causing tropomyosin to move and expose myosin-binding sites on actin.

Question 3

At the neuromuscular junction (NMJ), which type of neuron stimulates skeletal muscle contraction?

Accepted Answer

Somatic motor neuron

Question 4

Which of the following best describes a sarcomere?

Accepted Answer

The functional contractile unit of a muscle fiber, defined as the region between two Z discs

Question 5

Which two cell types synapse at the neuromuscular junction (NMJ)?

Accepted Answer

Motor neuron and skeletal muscle fiber

Question 6

Which neurotransmitter is released at the NMJ to initiate muscle contraction?

Accepted Answer

Acetylcholine

Question 7

A patient is exposed to a toxin that blocks acetylcholine receptors at the NMJ. What is the most likely effect on muscle contraction?

Accepted Answer

Muscle contraction will be inhibited because the action potential cannot be transmitted to the muscle fiber.

Question 8

During the sliding filament mechanism, which event occurs immediately after the myosin head forms a cross-bridge with actin?

Accepted Answer

The myosin head pivots, pulling the actin filament toward the center of the sarcomere (power stroke).

Question 9

Which molecule is required for the myosin head to detach from actin during muscle relaxation?

Accepted Answer

ATP

Question 10

Which of the following must occur for muscle relaxation to take place after contraction?

Accepted Answer

Calcium ions are actively transported back into the sarcoplasmic reticulum.

Question 11

A patient with myasthenia gravis produces antibodies against acetylcholine receptors. Which step in muscle contraction is most directly affected?

Accepted Answer

Transmission of the action potential from the neuron to the muscle fiber

Question 12

Which of the following best explains why rigor mortis occurs after death?

Accepted Answer

ATP is no longer produced, so myosin heads cannot detach from actin.

Question 13

Which of the following is the correct sequence of events in muscle contraction, starting with the arrival of an action potential at the NMJ?

Accepted Answer

Release of acetylcholine → depolarization of muscle fiber → release of $$\mathrm{Ca$$^{2+}$$}$$ from sarcoplasmic reticulum → binding of $$\mathrm{Ca$$^{2+}$$} to $$troponin → cross-bridge formation

Question 14

A drug inhibits the enzyme acetylcholinesterase at the NMJ. What is the most likely effect on muscle contraction?

Accepted Answer

Prolonged muscle contraction due to continued presence of acetylcholine in the synaptic cleft

Question 15

Which protein directly blocks the myosin-binding sites on actin in a relaxed muscle fiber?

Accepted Answer

Tropomyosin

Question 16

If a mutation prevents troponin from binding calcium, what would be the most immediate effect on muscle contraction?

Accepted Answer

Tropomyosin would not move, so myosin-binding sites on actin would remain covered.

Question 17

Which of the following best describes the function of the sarcoplasmic reticulum in muscle fibers?

Accepted Answer

It stores and releases calcium ions ($$\mathrm{Ca$$^{2+}$$}) $$necessary for muscle contraction.

Question 18

A patient is given a drug that blocks voltage-gated calcium channels in the axon terminal of a motor neuron. What is the most likely effect on the NMJ?

Accepted Answer

Acetylcholine release into the synaptic cleft will be inhibited, preventing muscle contraction.

Question 19

Which of the following equations best represents the hydrolysis of ATP during muscle contraction?

Accepted Answer

$$\mathrm{ATP} + \mathrm{H_2O} ightarrow \mathrm{ADP} + \mathrm{P_i} + 	ext{energy}$$

Muscle Tissue and Neuromuscular Junction: Study Guide

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