Question 1

A patient exposed to a neurotoxin presents with flaccid paralysis. Electrical stimulation of the motor neuron innervating the affected muscle produces no end-plate potential (EPP) and no increase in intracellular Ca$$^{2+} in $$the muscle fiber. Which of the following best explains these findings?

Accepted Answer

The neurotoxin is preventing acetylcholine (ACh) release from the motor neuron, such as botulinum toxin.

Question 2

Direct injection of acetylcholine (ACh) into the neuromuscular junction of a paralyzed muscle produces a normal end-plate potential (EPP), a significant increase in intracellular Ca$$^{2+}$$, but no force production. Which defect is most likely present?

Accepted Answer

A defect in the contractile proteins (e.g., actin or myosin) of the muscle fiber.

Question 3

After several weeks of therapy, a patient’s muscle produces a small amount of force with direct ACh injection, and increasing the frequency of motor neuron stimulation modestly increases force, but force remains far below normal. Which of the following best explains these findings?

Accepted Answer

Partial recovery of contractile protein function, but persistent structural damage limits maximal force.

Question 4

A patient’s ECG shows P waves at regular intervals, a prolonged PR interval, some P waves not followed by QRS complexes, and normal QRS duration. Which cardiac conduction abnormality is most likely present?

Accepted Answer

Second-degree AV block (Mobitz type I or II)

Question 5

After administration of a drug that increases sympathetic stimulation (β$$_1-$$adrenergic effect), a patient’s heart rate increases, the PR interval shortens, but some P waves are still not followed by QRS complexes. What does this suggest about the underlying cardiac conduction problem?

Accepted Answer

The AV node is partially refractory and cannot conduct all atrial impulses, even with increased sympathetic tone.

Question 6

During a cardiac cycle in which a P wave is not followed by a QRS complex, which of the following mechanical events is most likely to occur?

Accepted Answer

The atria contract, but the ventricles do not contract during that cycle.

Question 7

During a cardiac cycle with a QRS complex present, ventricular pressure is greater than atrial pressure but less than aortic pressure, and ventricular volume is decreasing. Which phase of the cardiac cycle does this describe?

Accepted Answer

Ventricular ejection phase

Question 8

During exercise, a patient has an increased heart rate, persistent episodes where some P waves are not followed by QRS complexes, and a lower-than-expected stroke volume. Which of the following is the most likely explanation?

Accepted Answer

Impaired AV conduction is limiting ventricular filling and output.

Question 9

Which of the following changes would most effectively increase blood flow to active skeletal muscles during exercise?

Accepted Answer

Decreased arteriolar resistance (vasodilation) in skeletal muscle

Question 10

During exercise, arterioles supplying skeletal muscle show less vasodilation than expected and capillary hydrostatic pressure is lower than expected. What is the most likely consequence for muscle perfusion?

Accepted Answer

Reduced blood flow and oxygen delivery to active muscle fibers

Question 11

During exercise, a patient’s capillary hydrostatic pressure is lower than expected, interstitial hydrostatic pressure is unchanged, capillary oncotic pressure is slightly increased (due to mild dehydration), and interstitial oncotic pressure is unchanged. What is the predicted effect on net capillary filtration?

Accepted Answer

Net filtration will decrease, leading to less fluid movement into the interstitial space.

Question 12

Despite an increased heart rate during exercise, a patient’s mean arterial pressure (MAP) does not rise as expected. Which of the following is the most likely explanation?

Accepted Answer

Cardiac output is not increasing sufficiently due to impaired ventricular filling.

Question 13

A transient drop in mean arterial pressure (MAP) during exercise triggers which of the following reflex responses?

Accepted Answer

Increased sympathetic outflow, leading to increased heart rate and vasoconstriction

Question 14

After donating 500 mL of blood, a patient’s heart rate is significantly higher during exercise at the same workload compared to before donation. Which of the following best explains this physiological response?

Accepted Answer

Decreased stroke volume due to reduced blood volume, compensated by increased heart rate to maintain cardiac output

Question 15

After blood donation, a patient maintains the same running pace but reports greater effort and earlier fatigue. What is the primary physiological limitation during her post-donation exercise?

Accepted Answer

Reduced oxygen-carrying capacity due to decreased hemoglobin concentration

Step-by-Step Guidance for Neuromuscular and Cardiovascular Physiology Case Study

Study Guide - Practice Questions

Study Guide - Flashcards