The following statements are made with reference to the neural connections of cardiac tissues and the functions of these nerves on heart in adult humans:

A. The right vagus nerve is distributed mainly to the AV node.

B. The parasympathetic pre-ganglionic fibers distributed to the heart originate from the superior salivatory nucleus.

C. The sympathetic post-ganglionic fibers originating from the paravertebral ganglia of the left side primarily innervate SA node.

D. The sympathetic fibers distributed to heart come mainly from stellate ganglia.

E. The sympathetic activity alters heart rate slower than that of vagal activity.

Which one of the following options represents the combination of all correct statements?

Correct option is D

Statement A: The right vagus nerve is distributed mainly to the AV node. Incorrect

• The right vagus nerve has more influence on the SA node (sinoatrial node), and the left vagus nerve predominantly affects the AV node.
• Hence, Statement A is not accurate.

Statement B: The parasympathetic pre-ganglionic fibers distributed to the heart originate from the superior salivatory nucleus.  Incorrect

• The parasympathetic pre-ganglionic fibers distributed to the heart actually originate from the dorsal motor nucleus of the vagus, not from the superior salivatory nucleus.
• Thus, this statement is incorrect.

Statement C: The sympathetic post-ganglionic fibers originating from the paravertebral ganglia of the left side primarily innervate the SA node.  Incorrect

• Sympathetic fibers that innervate the SA node and AV node come from both sides of the sympathetic chain (left and right), not just the left side.
• Therefore, this statement is incorrect.

Statement D: The sympathetic fibers distributed to the heart come mainly from stellate ganglia.  Correct

• The stellate ganglia (combination of inferior cervical and T1 sympathetic ganglia) contribute significantly to the sympathetic innervation of the heart.
• Sympathetic activity from these ganglia increases heart rate and contractility.
• Hence, this statement is correct.

Statement E: The sympathetic activity alters heart rate slower than that of vagal activity.  Correct

• Vagal (parasympathetic) activity has a faster effect on heart rate regulation (slowing it down), while sympathetic activity (through the release of norepinephrine) results in a slower increase in heart rate but with a longer-lasting effect.
• Thus, this statement is correct.

Information Booster:

1. Vagus nerve (parasympathetic) slows the heart rate (via the SA and AV nodes).
2. Sympathetic fibers (originating from the sympathetic chain and stellate ganglia) increase heart rate and contractility.
3. Sympathetic activity has a slower onset compared to parasympathetic effects, but its effects are more prolonged.
4. Sympathetic post-ganglionic fibers are essential in increasing the heart rate and force of contraction during stress or exercise.