Physiological Adaptation Q 185

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Stimulation of the sympathetic nervous system produces which of the following responses?

  

     A. Bradycardia

     B. Tachycardia

     C. Hypotension

     D. Decreased myocardial contractility

    

    

Correct Answer: B. Tachycardia

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Stimulation of the sympathetic nervous system causes tachycardia and increased contractility. Norepinephrine released from neurons via the right stellate ganglion increases heart rate and shortens atrioventricular conduction via the sinus and atrioventricular nodes.

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Option A: The parasympathetic nervous system is responsible for decreasing the heart rate. M1 receptors are the inhibitory receptors. They are present in the heart especially on the SA node and AV node. Activation of M1 receptors decreases heart rate. It does not have any effect on the force of contraction.

Option C: Hypotension is caused by the parasympathetic nervous system. The baroreceptor reflex stimulates the parasympathetic system. The PSNS causes relaxation of blood vessels, decreasing total peripheral resistance. It also decreases heart rate. As a result, blood pressure decreases.

Option D: Decreased myocardial contractility is related to the parasympathetic nervous system, which is responsible for slowing the heart rate.

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