**Purkinje Fibers: Specialized Cardiac Muscle Cells Responsible for Electrical Conduction**

**Definition and Location**

Purkinje fibers, also known as Purkinje cells or Purkinje network, are specialized cardiac muscle cells that play a crucial role in the electrical conduction system of the heart. These cells are located in the subendocardium, which is the inner layer of the heart's ventricles.

**Structure and Characteristics**

Purkinje fibers are large, branching cells that have a unique appearance compared to other cardiac muscle cells. They contain fewer contractile myofilaments and are characterized by a pale cytoplasm, large nuclei, and extensive sarcoplasmic reticulum. These structural features enable them to conduct electrical signals rapidly and efficiently throughout the ventricular myocardium.

**Function**

The primary function of Purkinje fibers is to rapidly transmit electrical impulses from the atrioventricular (AV) node to the ventricles, ensuring coordinated and synchronized contractions of the heart. These cells form a network of specialized conducting pathways that allow for the efficient spread of electrical signals.

**Electrical Conduction**

1. Initiation: The electrical signal starts in the sinoatrial (SA) node, the natural pacemaker of the heart, which generates regular electrical impulses.

2. Atrioventricular (AV) Node: The electrical impulses reach the AV node, where they are delayed for a short period to allow the atria to contract fully before the ventricles receive the signal.

3. Bundle of His: After the delay at the AV node, the electrical impulses are rapidly conducted through the bundle of His, a specialized pathway made up of conducting cells.

4. Purkinje Fibers: The electrical signals then spread from the bundle of His to the Purkinje fibers, which quickly distribute the impulses throughout the ventricles.

5. Myocardial Contraction: The electrical stimulation of the Purkinje fibers triggers the contraction of the ventricular myocardium, leading to the ejection of blood from the heart.

**Summary**

In summary, Purkinje fibers are specialized cardiac muscle cells located in the ventricles of the heart. Their unique structural characteristics and location allow for rapid conduction of electrical signals, ensuring coordinated contractions of the ventricular myocardium. These fibers form a crucial part of the heart's electrical conduction system, working in conjunction with other components such as the SA node, AV node, and bundle of His to maintain the proper functioning of the heart.