How does stimulation of the sympathetic nervous system affect cardiac function?
Solution
Correct Answer: Option C
Stimulation of the sympathetic nervous system has a significant impact on cardiac function. The sympathetic nervous system releases catecholamines, primarily norepinephrine and epinephrine, which bind to beta-1 adrenergic receptors in the heart. This interaction leads to several physiological effects:
1. Increased heart rate (positive chronotropic effect): Activation of beta-1 receptors speeds up the sinoatrial (SA) node firing rate, thus increasing the heart rate.
2. Increased myocardial contractility (positive inotropic effect): The strength of cardiac muscle contraction is enhanced, leading to more forceful heartbeats.
3. Increased conduction velocity (positive dromotropic effect): Conduction through the atrioventricular (AV) node is accelerated, which helps coordinate faster cardiac cycles.
Given these effects, the correct answer is Option 3: Increases heart rate. The other options are incorrect because sympathetic stimulation actually increases myocardial contractility, speeds up (not slows down) the heart rate, and enhances AV node conduction rather than reducing it.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th Edition, Chapter 15 - The Heart as a Pump and Function of the Heart Valves, Page 217
1. Increased heart rate (positive chronotropic effect): Activation of beta-1 receptors speeds up the sinoatrial (SA) node firing rate, thus increasing the heart rate.
2. Increased myocardial contractility (positive inotropic effect): The strength of cardiac muscle contraction is enhanced, leading to more forceful heartbeats.
3. Increased conduction velocity (positive dromotropic effect): Conduction through the atrioventricular (AV) node is accelerated, which helps coordinate faster cardiac cycles.
Given these effects, the correct answer is Option 3: Increases heart rate. The other options are incorrect because sympathetic stimulation actually increases myocardial contractility, speeds up (not slows down) the heart rate, and enhances AV node conduction rather than reducing it.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th Edition, Chapter 15 - The Heart as a Pump and Function of the Heart Valves, Page 217
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