Question 1

Which of the following best describes the role of chemically gated ion channels at the neuromuscular junction?

Accepted Answer

They open in response to binding of neurotransmitters such as acetylcholine.

Question 2

During the generation of an action potential across the sarcolemma, what is the primary effect of acetylcholine binding to its receptor?

Accepted Answer

It causes chemically gated sodium channels to open, allowing $$\mathrm{Na^+} to $$enter the muscle fiber.

Question 3

Which of the following sequences correctly lists the four steps required for skeletal muscle contraction?

Accepted Answer

1. Action potential arrives at axon terminal; 2. Acetylcholine released; 3. Calcium released from SR; 4. Cross bridge formation

Question 4

A patient is exposed to a toxin that blocks voltage-gated sodium channels on the sarcolemma. What is the most likely effect on muscle contraction?

Accepted Answer

Muscle contraction will be inhibited because the action potential cannot propagate along the sarcolemma.

Question 5

Which phase of the muscle twitch corresponds to the time when calcium is re-entering the sarcoplasmic reticulum?

Accepted Answer

Relaxation period

Question 6

What is the primary difference between isotonic and isometric muscle contractions?

Accepted Answer

Isotonic contractions change muscle length and move load, while isometric contractions generate force without changing muscle length.

Question 7

During cross bridge cycling, what event directly causes the detachment of the myosin head from actin?

Accepted Answer

Binding of ATP to the myosin head

Question 8

If a muscle fiber is repeatedly stimulated before it has a chance to relax, what phenomenon occurs?

Accepted Answer

Wave summation

Question 9

Which of the following best explains why increasing the frequency of stimulation leads to tetanus in muscle fibers?

Accepted Answer

Muscle fibers do not have time to relax between stimuli, causing sustained contraction.

Question 10

A muscle is contracting against a load that is greater than the maximum tension it can generate. What type of contraction is occurring?

Accepted Answer

Isometric contraction

Question 11

Which factor does NOT directly increase the force of muscle contraction?

Accepted Answer

Increasing the degree of muscle stretch beyond optimal length

Question 12

What is the role of the sodium-potassium pump ($$\mathrm{Na^+/K^+}$$ ATPase) during restoration of resting conditions after an action potential?

Accepted Answer

It pumps $$\mathrm{Na^+}$$ out of the cell and $$\mathrm{K^+}$$ into the cell.

Question 13

Which of the following best describes the 'motor unit' in skeletal muscle?

Accepted Answer

A single motor neuron and all the muscle fibers it innervates

Question 14

Which equation best represents the relationship between force of contraction and number of cross bridges formed?

Accepted Answer

$$F \propto N_{cb}$$, where $$F is $$force and $$N_{cb} is $$number of cross bridges

Question 15

A muscle fiber is exposed to a drug that prevents the reuptake of calcium into the sarcoplasmic reticulum. What is the most likely effect?

Accepted Answer

The muscle fiber will remain contracted and unable to relax.

Question 16

Which of the following is true regarding the latent period of a muscle twitch?

Accepted Answer

It is the period when excitation-contraction coupling occurs and no tension is seen.

Question 17

Which of the following best explains why smaller motor units allow for finer muscle control?

Accepted Answer

Smaller motor units contain fewer muscle fibers, allowing for more precise activation.

Question 18

Which of the following is a correct statement about eccentric contractions?

Accepted Answer

The muscle lengthens while generating force.

Question 19

Which of the following factors will increase the velocity of muscle contraction?

Accepted Answer

Recruiting more motor units

Question 20

A muscle fiber is stimulated with a subthreshold stimulus. What is the expected response?

Accepted Answer

No contraction will occur.

Muscle Fiber Contraction and Whole Muscle Physiology

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