17 Questions
What is the name of the specialized regions in cardiac muscle that have many desmosomes and adherent junctions joining the cells firmly?
Intercalated discs
Which structure surrounds the muscle cells in cardiac muscle and contains a rich capillary network?
Endomysium
What is the function of sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) in cardiac muscle cells?
To transport calcium ions back into the sarcoplasmic reticulum after muscle contraction
What is the main function of the fibrous skeleton in specific areas of cardiac muscle?
To separate bundles and layers of muscle fibers
Which part of the cardiac muscle cell plays a crucial role in coordinating excitation-contraction coupling by regulating calcium levels?
Intercalated discs
Which layer of the heart contains Purkinje fibers specialized for impulse conduction?
Subendocardial layer
What type of cells make up the Purkinje fibers in the heart?
Modified cardiac muscle cells
Which layer of the heart typically stains paler due to glycogen filling much of the cytoplasm?
Subendocardial layer
The mesothelium that lines the pericardial space also covers which layer of the heart?
Epicardium
What does the simple mesothelium secrete to prevent friction as the heart beats?
Lubricant fluid
Which layer of the heart includes an endothelium and a subendothelial connective tissue?
Endocardium
What is the main function of sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) in cardiac muscle relaxation?
Removal of 80% of Ca2+ from the sarcoplasm
Which component is responsible for the Ca2+-stimulated release of Ca2+ in cardiac muscle?
Ryanodine receptors
What is the function of Na+/K+ ATPase in cardiac muscle?
Maintaining Na+ concentration gradient for Na+/Ca2+ exchanger
Which type of channel opens upon the action potential conducted along the sarcolemma and T-tubules in cardiac muscle?
Voltage-gated Ca2+ channels
Where is the epicardium located within the cardiac muscle layers?
External tunic of the heart
What is responsible for forming cross-bridges and initiating the power stroke in cardiac muscle?
Ca2+ binding to troponin C
Study Notes
Epicardium
- The epicardium is the visceral layer of the pericardium and is covered by the simple mesothelium.
- The mesothelial cells secrete a lubricant fluid that prevents friction as the beating heart contacts the parietal pericardium.
Endocardium
- The endocardium is the lining layer of the heart, consisting of the endothelium and its supportive subendothelial connective tissue.
- It has a middle myoelastic layer of smooth muscle cells and connective tissue, and a deeper connective tissue layer of variable thickness called the subendocardial layer.
- The subendocardial layer in the ventricles contains the conducting (Purkinje) fibers of the heart's impulse conducting network.
- Purkinje fibers are modified cardiac muscle cells joined by intercalated disks but specialized for impulse conduction rather than contraction.
Cardiac Muscle Cells
- Cardiac muscle cells have nuclei, intercalated discs, and striations.
- Surrounding the muscle cells is a delicate sheath of endomysium with a rich capillary network.
- A thicker perimysium separates bundles and layers of muscle fibers and forms larger masses of fibrous connective tissue.
Intercalated Discs
- Transverse intercalated disc regions have many desmosomes and adherent junctions called fascia adherentes, which join the cells firmly.
Excitation-Contraction Coupling in Cardiac Muscle
- Ca2+-stimulated Ca2+ release is the mechanism of excitation-contraction coupling in cardiac muscle.
- Action potentials conducted along the sarcolemma and T-tubules open voltage-gated Ca2+ channels, leading to Ca2+ release from the SR.
- Ca2+ binds to troponin C, leading to the formation of cross-bridges and power stroke.
Cardiac Muscle Relaxation
- Ca2+ concentration in the cytoplasm is reduced by active transport back into the SR and removal of Ca2+ out of the cell through the plasma membrane.
- Myocardium relaxes when Ca2+ concentration is reduced.
Test your knowledge on the epicardium being the visceral layer of the pericardium and the different layers of cardiac muscles. This quiz is based on Junquiera's Basic Histology.
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