Multiple Choice Questions (MCQs)
- What property of the myocardium allows it to generate impulses spontaneously and rhythmically?
a) Elasticity
b) Automaticity
c) Extensibility
d) Conductivity
Answer: b) Automaticity - What is the duration of the absolute refractory period (ARP) in the ventricles?
a) 0.03 seconds
b) 0.05 seconds
c) 0.15 seconds
d) 0.25 seconds
Answer: d) 0.25 seconds - Which principle ensures that the cardiac muscle contracts as a single unit when a threshold stimulus is applied?
a) Treppe
b) All-or-None Principle
c) Refractory Principle
d) Syncytial Transmission
Answer: b) All-or-None Principle - What phenomenon describes progressively stronger contractions with repeated stimuli of constant strength?
a) Syncytium Effect
b) Treppe (Staircase Phenomenon)
c) Refractory Response
d) Myocardial Elasticity
Answer: b) Treppe (Staircase Phenomenon) - What is the significance of the long refractory period in cardiac muscle?
a) It allows faster contraction rates.
b) It prevents tetany, ensuring the heart relaxes and refills.
c) It improves myocardial elasticity.
d) It increases contraction velocity.
Answer: b) It prevents tetany, ensuring the heart relaxes and refills. - Which property of myocardium allows it to stretch after contraction?
a) Conductivity
b) Elasticity
c) Extensibility
d) Contractility
Answer: c) Extensibility - What happens during the relative refractory period (RRP) of cardiac muscle?
a) No stimulus can evoke a response.
b) A normal-strength stimulus causes contraction.
c) A stronger-than-normal stimulus can evoke a response.
d) Contraction is fully inhibited.
Answer: c) A stronger-than-normal stimulus can evoke a response. - How does cardiac muscle differ from skeletal muscle in contraction duration?
a) Cardiac muscle contractions are shorter.
b) Cardiac muscle contractions are longer.
c) Both have similar contraction durations.
d) Cardiac muscle contracts slower but shorter.
Answer: b) Cardiac muscle contractions are longer. - Which property ensures that myocardial cells return to their original length after stretching?
a) Extensibility
b) Elasticity
c) Conductivity
d) Rhythmicity
Answer: b) Elasticity - What is the mechanism behind the Treppe phenomenon?
a) Increased sarcoplasmic viscosity
b) Decreased heat production
c) Improved calcium availability and reduced sarcoplasmic viscosity
d) Shortened refractory period
Answer: c) Improved calcium availability and reduced sarcoplasmic viscosity
Fill in the Blanks
- The property of ________ allows the myocardium to maintain rhythm without external inputs.
Answer: automaticity - The ________ refractory period is a time during which no stimulus can evoke a response.
Answer: absolute - The ________ phenomenon is characterized by progressively stronger contractions with repeated stimuli.
Answer: Treppe (Staircase Phenomenon) - Cardiac muscle does not undergo tetany because of its ________ refractory period.
Answer: long - The ability of myocardial cells to stretch after contraction is called ________.
Answer: extensibility
True or False
- The refractory period is shorter in cardiac muscle compared to skeletal muscle.
Answer: False - The Treppe phenomenon enhances cardiac output by progressively increasing contraction strength.
Answer: True - Elasticity ensures the heart maintains its shape and function after each contraction.
Answer: True - Cardiac muscle follows the All-or-None Principle.
Answer: True - The absolute refractory period in the atria is longer than in the ventricles.
Answer: False
Subjective Questions
- Discuss the significance of the refractory period in cardiac muscle.
Answer: The refractory period in cardiac muscle is crucial for preventing tetany (continuous contractions), allowing the heart to relax and refill with blood between beats. The absolute refractory period ensures that no stimulus can trigger another contraction during the ongoing contraction, while the relative refractory period allows contraction only with a stronger-than-normal stimulus. This ensures a regular rhythm and optimal blood ejection and refilling during the cardiac cycle. - Explain the differences between cardiac and skeletal muscle in terms of contraction.
Answer:- Duration: Cardiac muscle contractions last longer due to the plateau phase of the action potential.
- Refractory Period: Cardiac muscle has a longer refractory period, preventing tetany.
- All-or-None Principle: Cardiac muscle contracts as a syncytium, meaning the entire muscle contracts if the stimulus is above the threshold. Skeletal muscle contractions can be graded.
- Impulse Transmission: Cardiac muscle transmits impulses rapidly through intercalated discs and gap junctions, behaving as a functional syncytium.
- Rate of Force Development and Velocity of Shortening: Both are slower in cardiac muscle compared to skeletal muscle, reflecting its role in continuous, rhythmic contractions.