Emergency Medical Technician (EMT) Intermediate Practice Exam

What is the result of stimulating beta receptors of the sympathetic nervous system?

1. Decreased heart rate

2. Increased myocardial contractility

3. Bronchoconstriction

4. Reduced blood pressure

The correct answer is: Increased myocardial contractility

Stimulating beta receptors of the sympathetic nervous system primarily leads to an increase in myocardial contractility. This effect is mainly mediated by beta-1 adrenergic receptors, which are predominantly found in the heart. When these receptors are activated, they enhance the strength of the heart's contractions, resulting in improved cardiac output. This mechanism is crucial during situations requiring a rapid response, such as in times of stress or emergency, when the body needs to pump more blood to vital organs and muscles. The other potential effects, like bronchoconstriction, are not associated with beta receptor stimulation; in fact, stimulation of beta-2 receptors leads to bronchodilation. Similarly, stimulating beta receptors does not typically result in decreased heart rate, as that is more associated with parasympathetic activity, and blood pressure may actually increase due to elevated heart contractility and increased cardiac output, not a reduction. Thus, the primary role of beta receptor stimulation in the sympathetic nervous system aligns with increased myocardial contractility, making it the correct response in this context.