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Atrial depolarization is the first part of the cardiac cycle.
Cardiac (and skeletal) muscle is made up of bundled stands of functional units called sarcomeres. Each sarcomere consists of two Z-disks, which mark the ends of each sarcomere, and alternating dark and light bands called A-bands and I-bands respectively. The I-band contains only actin (the main cytoskeletal protein in most cells) filaments whereas the A-band contains overlapping myosin (a "molecular motor" protein) and actin filaments in its periphery and only myosin filaments in the central region called the H-zone. The center of the H-zone is marked by an imaginary line (called the M-line) in which myosin extends in both directions. The sarcomere contracts inward toward the M-line. "Depolarization" occurs when an electrochemical event causes calcium cations to be released from a membranous network (similar to the the endoplasmic reticulum) called the sarcoplasmic reticulum and creates an action potential. The free Ca2+ binds to a specific troponin protein shifting a troponin/tropomyosin protein complex allowing the myosin head groups to bind to the actin filament. ATP hydrolysis causes conformational changes of the myosin filament which in effect "pulls" the actin filament toward the M-line of the sarcomere. The sarcomere can return to its resting potential by allowing potassium (K+) ions to flow out.
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What does P wave forms reflect?
P wave forms reflect atrial depolarization in the heart, specifically the spread of electrical activity through the atria causing them to contract. This is the initial wave seen on an electrocardiogram (ECG) tracing.
Immediately before the P wave?
The P wave represents atrial depolarization in an ECG, so it occurs just before the P wave on the ECG tracing. It signifies the activation of the atria as they prepare to contract and pump blood into the ventricles.
Why is the ECG event indicating atrial repolarization not seen in an ECG?
The atrial repolarization event is usually hidden by the larger QRS complex in the ECG, making it difficult to distinguish. The electrical activity from the atrial repolarization is masked by the ventricular depolarization signals.
Atrial repolarization coincides in time with?
the ventricular depolarization, which masks the atrial repolarization wave on the electrocardiogram. This is because the QRS complex is much larger than the atrial repolarization wave and overlaps with it, making it difficult to distinguish on the ECG.
The p wave corresponds to depolarization of the muscle fibers of the?
The P wave corresponds to atrial depolarization, specifically the spread of electrical impulses through the atria causing them to contract and pump blood into the ventricles. This is the first wave in an electrocardiogram (ECG) and represents the beginning of the cardiac cycle.
