QuestionJuly 30, 2026

How does the sympathetic nervous system affect the heart? It returns the heart to resting state contraction It causes the release of norepinephrine, which increases the rate of depolarization It releases hormones for muscle lengthening, which slows heart rate It causes an increase in the plateau phase

How does the sympathetic nervous system affect the heart? It returns the heart to resting state contraction It causes the release of norepinephrine, which increases the rate of depolarization It releases hormones for muscle lengthening, which slows heart rate It causes an increase in the plateau phase
How does the sympathetic nervous system affect the heart? It returns the heart to resting state contraction It causes the release of norepinephrine, which increases the rate of depolarization It releases hormones for muscle lengthening, which slows heart rate It causes an increase in the plateau phase

Solution
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Answer

It causes the release of norepinephrine, which increases the rate of depolarization Explanation 1. Identify the sympathetic nervous system's neurotransmitter The sympathetic nervous system releases norepinephrine (and epinephrine) onto the cardiac tissue. 2. Determine the effect on cardiac cells Norepinephrine binds to \beta_1-adrenergic receptors, activating a signaling cascade that increases the permeability of Na^+ and Ca^{2+} channels. This steepens the pacemaker potential slope, leading to a faster rate of depolarization. 3. Evaluate the options The increase in the rate of depolarization directly results in an increased heart rate (tachycardia), which is the primary function of the sympathetic nervous system on the heart.

Explanation

1. Identify the sympathetic nervous system's neurotransmitter<br />The sympathetic nervous system releases norepinephrine (and epinephrine) onto the cardiac tissue.<br /><br />2. Determine the effect on cardiac cells<br />Norepinephrine binds to $\beta_1$-adrenergic receptors, activating a signaling cascade that increases the permeability of $Na^+$ and $Ca^{2+}$ channels. This steepens the pacemaker potential slope, leading to a faster rate of depolarization.<br /><br />3. Evaluate the options<br />The increase in the rate of depolarization directly results in an increased heart rate (tachycardia), which is the primary function of the sympathetic nervous system on the heart.
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