Podcast
Questions and Answers
Why are ions able to move easily along the longitudinal axes of cardiac muscle fibers?
Why are ions able to move easily along the longitudinal axes of cardiac muscle fibers?
- Because of the intercalated discs that connect cardiac muscle cells (correct)
- Because of the absence of intercalated discs between cardiac muscle cells
- Because of the presence of fibrous tissue between the atria and ventricles
- Because of the presence of the A-V bundle
What is the function of the fibrous tissue that surrounds the atrioventricular (A-V) valvular openings?
What is the function of the fibrous tissue that surrounds the atrioventricular (A-V) valvular openings?
- To conduct action potentials from the atrial syncytium to the ventricular syncytium
- To allow ions to move freely between the atria and ventricles
- To electrically insulate the atria from the ventricles (correct)
- To mechanically separate the atria from the ventricles
What is the significance of the division of the heart muscle into two functional syncytiums?
What is the significance of the division of the heart muscle into two functional syncytiums?
- It allows the ventricles to contract before the atria
- It allows the atria to contract simultaneously with the ventricles
- It has no functional significance
- It allows the atria to contract a short time ahead of ventricular contraction (correct)
What is a major difference between cardiac muscle and skeletal muscle?
What is a major difference between cardiac muscle and skeletal muscle?
What is the function of specialized excitatory and conductive muscle fibers in the heart?
What is the function of specialized excitatory and conductive muscle fibers in the heart?
What is the average amplitude of the action potential recorded in a ventricular muscle fiber?
What is the average amplitude of the action potential recorded in a ventricular muscle fiber?
What is the arrangement of cardiac muscle fibers?
What is the arrangement of cardiac muscle fibers?
What is the function of gap junctions in cardiac muscle?
What is the function of gap junctions in cardiac muscle?
What is the purpose of the A-V bundle?
What is the purpose of the A-V bundle?
What is the type of filaments found in cardiac muscle myofibrils?
What is the type of filaments found in cardiac muscle myofibrils?
What is the duration of ventricular contraction in cardiac muscle compared to skeletal muscle?
What is the duration of ventricular contraction in cardiac muscle compared to skeletal muscle?
What is the duration of the plateau phase in the action potential of a ventricular muscle fiber?
What is the duration of the plateau phase in the action potential of a ventricular muscle fiber?
What is the difference in contraction duration between cardiac muscle and skeletal muscle?
What is the difference in contraction duration between cardiac muscle and skeletal muscle?
What is the characteristic of cardiac muscle that allows it to function as a single unit?
What is the characteristic of cardiac muscle that allows it to function as a single unit?
What type of junctions are formed between cardiac muscle cells at intercalated discs?
What type of junctions are formed between cardiac muscle cells at intercalated discs?
What is the intracellular potential of a ventricular muscle fiber between beats?
What is the intracellular potential of a ventricular muscle fiber between beats?
Study Notes
Physiology of Cardiac Muscle
- The heart is composed of three types of cardiac muscle: atrial muscle, ventricular muscle, and specialized excitatory and conductive muscle fibers.
- Atrial and ventricular muscles contract similarly to skeletal muscle, but with a longer contraction duration.
- Specialized excitatory and conductive fibers have few contractile fibrils, instead exhibiting automatic rhythmical electrical discharge or conduction of action potentials.
Physiologic Anatomy of Cardiac Muscle
- Cardiac muscle fibers are arranged in a latticework, dividing, recombining, and spreading again.
- Cardiac muscle is striated, similar to skeletal muscle, with typical myofibrils containing actin and myosin filaments.
- Cardiac muscle fibers are made up of many individual cells connected in series and in parallel with one another, forming a syncytium.
- Intercalated discs are cell membranes that separate individual cardiac muscle cells, allowing rapid diffusion of ions through permeable "communicating" junctions (gap junctions).
Cardiac Muscle Syncytium
- The heart is composed of two syncytiums: atrial syncytium and ventricular syncytium.
- The atrial syncytium constitutes the walls of the two atria, and the ventricular syncytium constitutes the walls of the two ventricles.
- The atria and ventricles are separated by fibrous tissue, and action potentials are not conducted directly through this tissue.
- Instead, action potentials are conducted through the A-V bundle, a specialized conductive system.
Action Potentials in Cardiac Muscle
- The action potential in a ventricular muscle fiber averages about 105 millivolts.
- The intracellular potential rises from a negative value (about −85 millivolts) to a positive value (about +20 millivolts) during each beat.
- The membrane remains depolarized for about 0.2 seconds, exhibiting a plateau, followed by abrupt repolarization.
- The plateau in the action potential causes ventricular contraction to last about 15 times as long as in skeletal muscle.
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Description
Learn about the composition and function of cardiac muscle, including atrial, ventricular, and specialized excitatory and conductive muscle fibers.
