Multiple Choice Questions (MCQs)
- What is the structural arrangement of cardiac muscle fibers in the myocardium?
a) Horizontal bundles
b) Spiral bundles
c) Random latticework
d) Parallel rows
Answer: b) Spiral bundles - What structure allows electrical signals to pass between cardiac muscle cells?
a) Desmosomes
b) Intercalated discs
c) Sarcoplasmic reticulum
d) Ryanodine receptors
Answer: b) Intercalated discs - Which part of the sarcoplasmic reticulum releases calcium during contraction?
a) T-tubules
b) L-tubules
c) Ryanodine receptors
d) Desmosomes
Answer: c) Ryanodine receptors - What is the function of T-tubules in cardiac muscle fibers?
a) Provide mechanical adhesion
b) House gap junctions
c) Contain voltage-gated calcium channels
d) Store oxygen for energy production
Answer: c) Contain voltage-gated calcium channels - What term describes the heart functioning as a single, coordinated unit?
a) Mechanical syncytium
b) Functional syncytium
c) Synchronized myopathy
d) Lattice contraction
Answer: b) Functional syncytium - What separates the atrial syncytium from the ventricular syncytium?
a) Sarcoplasmic reticulum
b) Fibrous tissue around the valves
c) T-tubules
d) Intercalated discs
Answer: b) Fibrous tissue around the valves - Which of the following is NOT a characteristic of cardiac muscle fibers?
a) Striated appearance
b) Multinucleated
c) Mononucleated
d) Lattice-like arrangement
Answer: b) Multinucleated - What regulates the diffusion of ions through gap junctions in cardiac muscle cells?
a) Sodium ions
b) Potassium ions
c) Calcium ions and second messengers
d) Desmosomes
Answer: c) Calcium ions and second messengers - What ensures atria contract before ventricles?
a) Desmosomes
b) Specialized conduction system
c) Intercalated discs
d) Ryanodine receptors
Answer: b) Specialized conduction system - Which organelle is less developed in cardiac muscle compared to skeletal muscle?
a) Mitochondria
b) Sarcoplasmic reticulum (L-tubules)
c) T-tubules
d) Nucleus
Answer: b) Sarcoplasmic reticulum (L-tubules)
Fill in the Blanks
- The myocardium is composed of cardiac muscle fibers arranged in a _________ fashion.
Answer: spiral - _________ are fused cell membranes that connect individual cardiac muscle cells.
Answer: Intercalated discs - Calcium ions are released from _________ receptors during contraction.
Answer: Ryanodine - The _________ syncytium refers to the muscle mass of the atria.
Answer: atrial - The _________ arrangement of fibers enhances the efficiency of blood propulsion.
Answer: spiral
True or False
- The cardiac muscle fibers are multinucleated.
Answer: False - Gap junctions in intercalated discs allow ions to diffuse freely between cells.
Answer: True - The sarcoplasmic reticulum in cardiac muscle is more developed than in skeletal muscle.
Answer: False - Fibrous tissue separates the atrial and ventricular syncytia.
Answer: True - T-tubules in cardiac muscle contain voltage-gated calcium channels.
Answer: True
Subjective Questions
- Explain the significance of intercalated discs in cardiac muscle function.
Answer: Intercalated discs are specialized structures that connect individual cardiac muscle cells. They contain desmosomes, which provide mechanical strength, and gap junctions, which enable electrical connectivity by allowing ions to pass between cells. This connectivity ensures synchronized contraction, allowing the heart to function as a functional syncytium. - Discuss the role of calcium ions in cardiac muscle contraction.
Answer: Calcium ions play a critical role in cardiac muscle contraction. During depolarization, calcium enters the cells through voltage-gated channels in the T-tubules. Ryanodine receptors on the L-tubules release additional calcium, triggering the interaction of actin and myosin filaments for contraction. This process ensures efficient and synchronized muscle contraction. Calcium also regulates gap junction activity, aiding in the coordination of cardiac function.