Final answer:
Sympathetic stimulation of the AV node reduces the AV nodal delay by enhancing the inward current of calcium ions (Ca⁺), leading to a faster conduction velocity and decreased delay in the cardiac conduction system.
Step-by-step explanation:
Sympathetic Stimulation and AV Nodal Delay
When considering the effects of sympathetic stimulation on the atrioventricular (AV) node within the cardiac conduction system, it is noted that this stimulation leads to a reduction in AV nodal delay. This is achieved by increasing the conduction velocity which results from enhancing the inward current of an element. The specific element responsible for this action under sympathetic influence is calcium.
Sympathetic stimulation causes the release of norepinephrine (NE) at the neuromuscular junction of the cardiac nerves, leading to the opening of sodium and calcium ion channels. This allows an influx of positively charged ions, specifically calcium ions (Ca⁺), which play a pivotal role in cardiac muscle physiology. They are involved in the plateau phase of the cardiac action potential and are essential for the contraction mechanism of myocardial cells. Consequently, sympathetic stimulation that leads to increased calcium influx simultaneously reduces the AV nodal delay.