What effects does the autonomic system have on heart?

Parasympathetic Effects:

1. Heart Rate: The parasympathetic system decreases the heart rate by slowing down the rate of electrical impulses generated by the sinoatrial node (SA node). This effect is mediated primarily through the vagus nerve.

2. Contractility: Parasympathetic stimulation reduces myocardial contractility, decreasing the force of heart contractions.

3. AV Conduction: The vagus nerve can cause slight delays in the conduction of electrical impulses from the atria to the ventricles through the atrioventricular node (AV node).

Sympathetic Effects:

1. Heart Rate: The sympathetic nervous system increases the heart rate by accelerating the electrical impulses generated by the SA node.

2. Contractility: Sympathetic stimulation enhances myocardial contractility, leading to more forceful heart contractions.

3. AV Conduction: The sympathetic system facilitates faster conduction of electrical impulses through the AV node, enabling more efficient transmission of signals from atria to ventricles.

4. Vasodilation and Constriction: Sympathetic stimulation can indirectly affect the heart by causing constriction or dilation of blood vessels in the coronary circulation. Constriction reduces blood supply to the heart, while dilation enhances it.

5. Arrhythmias: Excessive sympathetic activity can lead to abnormal heart rhythms, such as tachycardia (rapid heart rate) or arrhythmias (irregular heart rate).

Overall, the autonomic nervous system plays a crucial role in regulating the heart's rate, contractility, and electrical conduction. While the parasympathetic system generally slows down the heart and its activities, the sympathetic system acts to accelerate and strengthen the heart's function, preparing the body for physical or stressful situations.