**Core Concept**
Purkinje fibers are specialized cardiac conduction fibers responsible for transmitting electrical impulses from the atrioventricular (AV) node to the ventricles, ultimately leading to coordinated ventricular contraction.

**Why the Correct Answer is Right**
The correct answer is related to the unique characteristic of Purkinje fibers. They have a high density of sodium channels, which allows for rapid depolarization and efficient transmission of electrical impulses throughout the ventricles. This property enables the coordinated contraction of the ventricular muscle cells, resulting in effective cardiac function. The Purkinje fibers also have a high concentration of calcium channels, which helps in the regulation of calcium ion influx and the subsequent contraction of cardiac muscle cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because, unlike Purkinje fibers, cardiac muscle cells have a lower density of sodium channels, which affects their excitability and contraction properties.
**Option B:** This option is incorrect because, while the action potential duration in Purkinje fibers is indeed longer than in ventricular muscle cells, it is not the primary characteristic that distinguishes them.
**Option D:** This option is incorrect because, although the conduction velocity in Purkinje fibers is indeed faster than in ventricular muscle cells, it is not the correct answer choice.

**Clinical Pearl / High-Yield Fact**
The Purkinje fibers play a critical role in maintaining the normal rhythm of the heart. Any disruption in their function, such as in conditions like Wolff-Parkinson-White syndrome or Lown-Ganong-Levine syndrome, can lead to abnormal cardiac rhythms and potentially life-threatening complications.

**Correct Answer: C. Purkinje fibers have a high density of sodium channels, which allows for rapid depolarization and efficient transmission of electrical impulses.**