Q: Which of the following equations correctly represents the synthesis of acetylcholine in the presynaptic neuron?

$$\text{Acetyl CoA} + \text{Choline} \xrightarrow{\text{Choline acetyltransferase}} \text{Acetylcholine} + \text{CoA}$$

Q: In skeletal muscle, what is the ultimate intracellular signal that triggers contraction?

A rise in intracellular calcium concentration $$[\text{Ca}^{2+}]_i$$

Question 1

Which of the following best describes the function of the neuromuscular junction?

Accepted Answer

It is the site where a motor neuron communicates with a muscle fiber to initiate contraction.

Question 2

What is the primary neurotransmitter released at the neuromuscular junction?

Accepted Answer

Acetylcholine

Question 3

Which enzyme is responsible for breaking down acetylcholine in the synaptic cleft?

Accepted Answer

Acetylcholinesterase

Question 4

A patient with myasthenia gravis is likely to experience muscle weakness because:

Accepted Answer

Their body produces antibodies that block acetylcholine receptors on the muscle membrane.

Question 5

Which of the following is TRUE regarding the structure of a motor unit?

Accepted Answer

It consists of a single motor neuron and all the muscle fibers it innervates.

Question 6

Which ion is primarily responsible for generating the end-plate potential (EPP) at the motor end plate?

Accepted Answer

Na$$^{+}$$

Question 7

What is the role of the DHP receptor in excitation-contraction coupling?

Accepted Answer

It acts as a voltage-sensitive L-type Ca$$^{2+}$$ channel that triggers opening of RyR Ca$$^{2+}$$ release channels.

Question 8

Which of the following best explains why ALS leads to muscle atrophy?

Accepted Answer

ALS causes degeneration of motor neurons, resulting in decreased stimulation and disuse of muscle fibers.

Question 9

During muscle contraction, which event occurs immediately after acetylcholine binds to its receptor on the motor end plate?

Accepted Answer

Na$$^{+}$$ ions enter the muscle fiber, generating an end-plate potential.

Question 10

Which of the following equations correctly represents the synthesis of acetylcholine in the presynaptic neuron?

Accepted Answer

$$	ext{Acetyl CoA} + 	ext{Choline} \xrightarrow{	ext{Choline acetyltransferase}} 	ext{Acetylcholine} + 	ext{CoA}$$

Question 11

Which structure is responsible for propagating action potentials deep into the muscle fiber?

Accepted Answer

T-tubules

Question 12

In skeletal muscle, what is the ultimate intracellular signal that triggers contraction?

Accepted Answer

A rise in intracellular calcium concentration $$[	ext{Ca}^{2+}]_i$$

Question 13

Which of the following statements about the sarcomere is correct?

Accepted Answer

The Z disk anchors the actin filaments.

Question 14

Which process is NOT vital for skeletal muscle contraction, but is important in cardiac muscle?

Accepted Answer

Ca$$^{2+}-$$induced Ca$$^{2+}$$ release from the sarcoplasmic reticulum

Question 15

Which of the following best describes the effect of acetylcholinesterase inhibitors in the treatment of myasthenia gravis?

Accepted Answer

They prevent the breakdown of acetylcholine, prolonging its action at the neuromuscular junction.

Question 16

Which of the following is a characteristic of the nicotinic acetylcholine receptor at the motor end plate?

Accepted Answer

It is a ligand-gated monovalent cation channel permeable to Na$$^{+}$$ and K$$^{+}.$$

Question 17

A muscle fiber is unable to contract after repeated stimulation. Which of the following is the most likely cause?

Accepted Answer

Destruction of acetylcholine receptors by autoimmune antibodies

Question 18

Which of the following best describes the sequence of events in excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential → acetylcholine release → Na$$^{+}$$ influx → T-tubule depolarization → DHP receptor activation → RyR channel opening → Ca$$^{2+}$$ release

Question 19

Which of the following is a consequence of degeneration of postjunctional folds in myasthenia gravis?

Accepted Answer

Reduced surface area for acetylcholine receptors, leading to decreased muscle activation.

muscle 2

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