Question 1

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

Accepted Answer

They open when chemical messengers such as neurotransmitters bind to them.

Question 2

During the generation of an action potential in a skeletal muscle fiber, what is the primary event that triggers depolarization?

Accepted Answer

Binding of acetylcholine (ACh) to its receptor, causing Na+ influx.

Question 3

Which equation best represents the movement of ions during the end plate potential at the neuromuscular junction?

Accepted Answer

$$\Delta V = g_{Na^+}(E_{Na^+} - V_{m}) + g_{K^+}(E_{K^+} - V_{m})$$

Question 4

What is the consequence of acetylcholine (ACh) remaining in the synaptic cleft after its release?

Accepted Answer

Continuous stimulation of the muscle fiber, potentially leading to muscle spasms.

Question 5

Which process is responsible for restoring the resting membrane potential after an action potential in a muscle fiber?

Accepted Answer

Efflux of K+ through voltage-gated K+ channels.

Question 6

A patient is exposed to a toxin that blocks voltage-gated Na+ channels in skeletal muscle. What is the most likely effect?

Accepted Answer

Muscle fibers will be unable to depolarize and contract.

Question 7

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

Accepted Answer

ATP is no longer synthesized, preventing detachment of myosin heads from actin.

Question 8

Which step in excitation-contraction coupling directly leads to the release of calcium ions from the sarcoplasmic reticulum?

Accepted Answer

Propagation of the action potential down the T tubules.

Question 9

During cross bridge cycling, what is the role of ATP in muscle contraction?

Accepted Answer

ATP binds to myosin, causing cross bridge detachment from actin.

Question 10

Which type of muscle contraction occurs when muscle tension increases but the muscle does not change length?

Accepted Answer

Isometric contraction

Question 11

A weightlifter is lowering a heavy barbell. Which type of contraction is primarily occurring in the biceps brachii?

Accepted Answer

Eccentric isotonic contraction

Question 12

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

Accepted Answer

Decreasing the number of motor units recruited

Question 13

Which muscle fiber type is best suited for endurance activities such as maintaining posture?

Accepted Answer

Slow oxidative fibers

Question 14

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

Accepted Answer

Temporal (wave) summation

Question 15

Which equation describes the relationship between force, cross bridges, and muscle contraction?

Accepted Answer

$$F_{muscle} \propto n_{cross\ bridges}$$

Question 16

A sprinter relies on which muscle fiber type for short bursts of intense activity?

Accepted Answer

Fast glycolytic fibers

Question 17

What is the effect of increasing the load on a contracting muscle?

Accepted Answer

The velocity of contraction decreases and the duration shortens.

Question 18

Which of the following best explains the refractory period in a muscle fiber?

Accepted Answer

The muscle fiber cannot be stimulated again until repolarization is complete.

Question 19

Which event marks the beginning of the latent period in a muscle twitch?

Accepted Answer

Initiation of excitation-contraction coupling after the action potential arrives at the muscle fiber.

Question 20

Which process is responsible for pumping Na+ out of and K+ into the muscle cell to restore ionic conditions after an action potential?

Accepted Answer

Na+-K+ pump (sodium-potassium ATPase)

Chapter 9 Part 2 notes

Study Guide - Practice Questions