Multiple Choice
Which structure or structures are most directly responsible for allowing contraction of the ventricles to begin at the apex of the heart rather than in the septum closer to the AV node?
18. The Heart
Electrical Conduction System of the Heart
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The contractile cardiac muscle fibers of the myocardium behave as a single, coordinated unit called a __________.
A
sarcomere
B
functional syncytium
C
pacemaker
D
contractile unit
E
cardiac cycle
Verified step by step guidance1
Understand the concept of a 'functional syncytium': In cardiac muscle tissue, the cells are connected by intercalated discs, which allow for rapid transmission of electrical impulses. This enables the cardiac muscle fibers to contract in a coordinated manner, functioning as a single unit.
Identify the role of intercalated discs: These structures contain gap junctions that facilitate the direct passage of ions and electrical impulses between cardiac cells, ensuring synchronized contraction.
Differentiate between the terms: A 'sarcomere' is the basic contractile unit of muscle fiber, 'pacemaker' refers to cells that set the heart rate, 'contractile unit' is a general term for muscle contraction, and 'cardiac cycle' describes the sequence of events in a heartbeat.
Recognize that 'functional syncytium' is the term that best describes the coordinated contraction of cardiac muscle fibers as a single unit.
Conclude that the correct term for the behavior of contractile cardiac muscle fibers as a single, coordinated unit is 'functional syncytium'.
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