Question 1

During the latent period of skeletal muscle contraction, which sequence correctly describes the events from acetylcholine release to calcium entry into the cytosol?

Accepted Answer

Acetylcholine binds to nicotinic receptors, sodium influx depolarizes the sarcolemma, triggering an action potential that travels down the T-tubules, leading to calcium release from the sarcoplasmic reticulum.

Question 2

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

Accepted Answer

Calcium binds to troponin, causing a conformational change that moves tropomyosin off the actin binding sites, enabling cross-bridge formation.

Question 3

A motor unit is defined as:

Accepted Answer

A group of muscle fibers innervated by a single motor neuron.

Question 4

During the relaxation phase of muscle contraction, which event occurs first after action potentials cease?

Accepted Answer

Calcium is actively pumped back into the sarcoplasmic reticulum by the $$\mathrm{Ca$$^{2+}$$}-$$ATPase.

Question 5

Why are smaller motor units recruited before larger ones during skeletal muscle contraction?

Accepted Answer

Smaller motor units have lower thresholds for activation, allowing for finer and more precise movements.

Question 6

If a striated muscle is not held at its optimal length, what happens to its force production?

Accepted Answer

Force production decreases because the overlap between actin and myosin is either too great or too little, reducing cross-bridge formation.

Question 7

Which physical task would be performed fastest, and why: doing 20 bicep curls with a 3-pound weight or a 20-pound weight?

Accepted Answer

20 curls with a 3-pound weight, because smaller motor units are recruited first and fatigue less quickly.

Question 8

Which statement best describes Starling’s Law of the heart?

Accepted Answer

The greater the venous return, the greater the stroke volume due to increased stretching of cardiac muscle fibers.

Question 9

How does decreasing arterial elasticity affect afterload?

Accepted Answer

Afterload increases because stiffer arteries resist blood flow, requiring more force from the heart.

Question 10

Which effect does epinephrine have on the heart?

Accepted Answer

It increases stroke volume and heart rate by enhancing calcium influx and pacemaker activity.

Question 11

During the ventricular ejection phase of the cardiac cycle, what is the status of the AV and semilunar valves?

Accepted Answer

AV valves are closed, semilunar valves are open.

Question 12

Which ion channels are primarily responsible for the action potential in cardiac pacemaker cells?

Accepted Answer

Calcium T-type and L-type channels, along with potassium channels.

Question 13

What does the QRS complex represent in an ECG?

Accepted Answer

Ventricular depolarization and the onset of ventricular contraction.

Question 14

During isovolumetric contraction, what is the status of the heart valves and myocardial force?

Accepted Answer

Both AV and semilunar valves are closed; myocardial force is increasing.

Question 15

Which pathway correctly outlines the conducting system of the heart?

Accepted Answer

SA node → AV node → Bundle of His → Purkinje fibers

Question 16

Compare excitation-contraction coupling in cardiac and skeletal muscle. Which statement is correct?

Accepted Answer

Skeletal muscle uses $$\mathrm{Ca$$^{2+}$$}$$ released from the sarcoplasmic reticulum, while cardiac muscle uses both extracellular and sarcoplasmic $$\mathrm{Ca$$^{2+}$$}.$$

Question 17

During atrial contraction and ventricular filling, what is the state of the valves and ventricular volume?

Accepted Answer

AV valves are open, semilunar valves are closed; ventricular volume increases.

Question 18

Which of the following best defines stroke volume ($$SV) in $$cardiac physiology?

Accepted Answer

The volume of blood ejected by a ventricle during one contraction.

Question 19

A patient with reduced venous return is likely to experience which change according to Starling’s Law?

Accepted Answer

Decreased stroke volume due to less stretching of cardiac fibers.

Anatomy & Physiology Study Guide: Muscle Physiology and Cardiac Function

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