28 Questions
Why is the T wave more spread out and has a lower amplitude than the QRS complex?
Because depolarization is faster than repolarization
What is the purpose of the P wave?
Represents the movement of the depolarization wave from the SA node through the atria
Why is the wave representing atrial repolarization normally obscured by the large QRS complex?
Because atrial repolarization takes place during the period of ventricular excitation
How long after the P wave begins does the atria contract?
0.1 s
What is the fundamental difference in terms of the length of the absolute refractory period between skeletal muscle fibers and cardiac muscle cells?
Skeletal muscle fibers have a shorter absolute refractory period than cardiac muscle cells.
Why does the long refractory period in cardiac muscle cells prevent tetanic contractions?
It ensures that the heart's contractions are not continuous and do not interfere with each other.
What triggers cardiac muscle contraction?
Action potentials sweeping across cell membranes
What is the special ability of about 1% of cardiac muscle fibers?
To pace the heart by spontaneous depolarization
In which type of muscle cells does depolarization open fast voltage-gated Na+ channels?
Skeletal muscle fibers
What is the role of contractile muscle fibers in the heart?
To perform the heart's pumping activity
What is the main difference between the energy metabolism of cardiac muscle and skeletal muscle?
Cardiac muscle is more adaptable and can switch between different metabolic pathways, while skeletal muscle is more limited.
Why is the lack of oxygen supply to the myocardium (heart muscle) more dangerous than the lack of nutrients?
The heart requires a constant supply of oxygen to maintain its contractile function, and cannot tolerate even brief periods of hypoxia.
How do the fuel sources used by cardiac muscle and skeletal muscle differ?
Both cardiac muscle and skeletal muscle can use multiple fuel molecules, including glucose and fatty acids.
What is the main advantage of the heart's ability to switch between different metabolic pathways?
It allows the heart to maintain a constant supply of energy, even when the availability of specific nutrients changes.
What is the key difference between the energy metabolism of cardiac muscle and skeletal muscle during prolonged exercise?
Cardiac muscle relies more on anaerobic respiration, while skeletal muscle relies more on aerobic respiration.
What is the main reason why the heart is more dependent on a constant supply of oxygen compared to skeletal muscle?
The heart's energy production is more tightly coupled to its oxygen supply, and it cannot tolerate even brief periods of hypoxia.
What triggers the release of the other 80% of calcium needed for muscle contraction in cardiac cells?
Voltage change due to Na+-dependent membrane depolarization
Why does the influx of Ca2+ through slow Ca2+ channels trigger the opening of nearby Ca2+-sensitive channels in the sarcoplasmic reticulum (SR)?
To liberate bursts of Ca2+ that increase intracellular Ca2+ concentration
What effect does the calcium surge across the sarcolemma have on depolarization potential?
Prolongs it briefly
What role do the K+ channels play during muscle contraction?
Prevent rapid repolarization
Why is calcium barred from entering nonstimulated cardiac fibers?
Absence of Na+-dependent membrane depolarization
What is the primary function of slow Ca2+ channels in cardiac muscle cells?
To delay calcium entry and trigger SR channel opening
What is the primary function of the fibrous pericardium?
To anchor the heart to surrounding structures
Which layer of the pericardium forms a closed sac around the heart?
The serous membrane
What is the approximate location of the heart in the thorax?
Two-thirds to the left of the midsternal line
Which statement about the heart's position is correct?
The heart is positioned lower in the thorax when standing than when lying down
What is the primary function of the serous membrane's parietal layer?
To line the internal surface of the fibrous pericardium
What is the relationship between the heart and the lungs?
The heart is partially surrounded by the lungs
Learn about the approximate location of the heart in the mediastinum, its relationship to the sternum, ribs, and diaphragm, and its position when a person is lying down or standing. Explore the inferior view of a cross-section showing the heart's relative position in the thorax.
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