What distinguishes the contraction stimulus of cardiac contractile cells from that of skeletal muscle fibers?
Skeletal muscle fibers are activated by somatic motor neurons, while cardiac cells generate action potentials via pacemaker activity.
Cardiac contractile cells require anaerobic metabolism, whereas skeletal fibers depend solely on aerobic metabolism.
Cardiac cells require direct stimulation from motor neurons, while skeletal fibers generate their own action potentials.
Skeletal muscle fibers have a long refractory period, unlike cardiac cells.
The Correct Answer is A
A. Skeletal muscle fibers are activated by somatic motor neurons, while cardiac cells generate action potentials via pacemaker activity: Skeletal muscle fibers are innervated by somatic motor neurons, and each action potential originates from an external neural stimulus at the neuromuscular junction. Cardiac contractile cells, in contrast, can depolarize spontaneously due to pacemaker cells in the sinoatrial node, generating intrinsic action potentials that propagate through gap junctions without direct neural input.
B. Cardiac contractile cells require anaerobic metabolism, whereas skeletal fibers depend solely on aerobic metabolism: Both cardiac and skeletal muscle fibers primarily rely on aerobic metabolism to meet energy demands. Cardiac muscle has a high density of mitochondria for continuous aerobic ATP production, whereas skeletal muscle can use both aerobic and anaerobic pathways depending on activity intensity.
C. Cardiac cells require direct stimulation from motor neurons, while skeletal fibers generate their own action potentials: Cardiac contractile cells do not require direct neural stimulation; they depolarize via pacemaker activity and conduct impulses through the myocardium. Skeletal fibers, on the other hand, rely entirely on motor neuron input to initiate contraction and cannot generate spontaneous action potentials.
D. Skeletal muscle fibers have a long refractory period, unlike cardiac cells: The refractory period of cardiac contractile cells is much longer than that of skeletal muscle fibers. This prolonged refractory period prevents tetanic contractions in the heart, allowing sufficient time for filling between beats.
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Related Questions
Correct Answer is A
Explanation
A. Atrial cells have a resting potential of -80 mV, while ventricular cells have a resting potential of -90 mV: Cardiac contractile cells maintain a negative resting membrane potential due to selective permeability to potassium ions and the activity of the Na+/K+ ATPase pump. Atrial myocytes have a resting potential around -80 mV, while ventricular myocytes are slightly more negative at approximately -90 mV.
B. Both atrial and ventricular cells have a resting potential of -70 mV: A resting potential of -70 mV is characteristic of neurons, not cardiac contractile cells. Cardiac myocytes require a more negative resting potential to maintain proper excitability and ensure effective action potential generation for coordinated contraction.
C. Atrial cells have a resting potential of -90 mV, while ventricular cells have a resting potential of -80 mV: This reverses the actual values of atrial and ventricular cells. Ventricular cells are more polarized than atrial cells at rest due to higher potassium conductance and greater expression of inward-rectifier potassium channels.
D. Both atrial and ventricular cells have a resting potential of -60 mV: A resting potential of -60 mV is typical of pacemaker (autorhythmic) cells, such as those in the sinoatrial node, rather than contractile myocytes. Contractile cells require a more negative resting potential to maintain a stable resting state before depolarization.
Correct Answer is A
Explanation
A. Chordae tendinae: The structure pointed to by the line is the chordae tendineae. The chordae tendineae are strong, fibrous collagen cords that connect the atrioventricular valve leaflets (mitral and tricuspid valves) to the papillary muscles within the ventricles. They prevent valve prolapse during ventricular systole. When the ventricles contract, papillary muscles also contract, maintaining tension on the chordae tendineae to keep the valves closed and prevent backflow into the atria.
B. Papillary Muscles: Papillary muscles are cone-shaped projections from the ventricular walls that anchor chordae tendineae. During ventricular contraction, they prevent valve prolapse by maintaining tension on valve leaflets, ensuring unidirectional blood flow
C. Septal leaflet: The septal leaflet is part of the tricuspid valve attached to the interventricular septum. Chordae tendineae connect it to papillary muscles, stabilizing the valve during systole and preventing backflow into the right atrium.
D: Pulmonary vein: Pulmonary veins are vessels transporting oxygenated blood from the lungs to the left atrium. They are not directly connected to chordae tendineae but are adjacent to atrial structures influencing left atrial filling and valve dynamics.
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