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Structure
Purkinje fibers are modified cardiac muscle cells located in the bundle of His, in the deepest layer of the endocardium. Their structure is especially adapted for the rapid conduction of electrical signals to the apex of the heart. The Purkinje fibers are long strands of barrel-shaped cells with a few myofibrils arranged peripherally around a clear core of sarcoplasm. The wide central region of Purkinje fiber cells is rich in glycogen and mitochondria. Purkinje fibers form gap junctions, fasciae adherents and desmosomes with cardiac muscle cells, but not through the typical intercalated disks that normally link cardiac myocytes. The fibers extend down the interventricular septum, penetrate into the heart apex and then branch up the lateral walls of the ventricles. This arrangement ensures that the Purkinje fibers deliver the impulse for contraction such that the ventricular contractions begin at the apex of the heart and then spread up the lateral walls of the ventricles. As such the Purkinje fibres form an essential component of the sequence of excitation in the heart's contractile system.
Function
Purkinje fibers are modified cardiac muscle cells located in the bundle of His, in the deepest layer of the endocardium. Their structure is especially adapted for the rapid conduction of electrical signals to the apex of the heart. Purkinje fibers form gap junctions, fasciae adherents and desmosomes with cardiac muscle cells, but not through typical intercalated disks. The fibers extend down the interventricular septum, penetrate into the heart apex and then branch up the lateral walls of the ventricles. This arrangement ensures that the Purkinje fibers deliver the impulse for contraction such that the ventricular contractions begin at the apex of the heart and then spread up the lateral walls of the ventricles. Ventricular depolarization is mainly dependent on Purkinje fibers and ultimately, on the cell-to-cell transmission of the electrical impulse via gap junctions between the ventricular muscle cells. Consequently, they form an essential component of the sequence of excitation in the contractile system.
