Final answer:
The increase in the rate of heart conduction is facilitated by activation of the sympathetic nervous system, which releases norepinephrine, leading to a quicker pace of depolarization and an accelerated heartbeat.
Step-by-step explanation:
The mechanism responsible for increasing the rate of heart conduction is activation of the sympathetic nervous system. This system releases the neurotransmitter norepinephrine which binds to adrenergic receptors in the heart, leading to a faster depolarization of cardiac cells. When these receptors are activated, they increase the heart rate by speeding up the electrical signals that stimulate the heartbeat.
When the sympathetic nervous system is stimulated, it permits an influx of positive ions through ion channels in the heart muscles, which reduces the repolarization time, allowing the heart to depolarize and contract more quickly. This mechanism is important for responding to situations demanding increased cardiac output, such as during physical activity.
Contrarily, the parasympathetic nervous system decelerates heart rate by releasing acetylcholine (ACh), which hyperpolarizes cardiac cells, making it more difficult to reach the threshold for depolarization. Intercalated discs and sarcomeres are involved in cardiac muscle contraction and electrical signal transmission between cells, but do not directly affect the rate of heart conduction.