Purkinje fibers are specialized muscle fibers found in the heart. They originate at the atrioventricular bundle and extend into the ventricles. Their function is to relay impulses from the bundle to the ventricles, causing a contraction. They do so at a speed of between three ft (one m) and 12 ft (four m) per second, causing the contraction of the ventricles to be almost instantaneous.
These fibers, also known as subendocardial branches, are located beneath the endocardium, which is the innermost layer of the heart. Purkinje fibers are stretched along heart muscle tissue beginning at the atrioventricular node. They then proceed down the middle portion of the heart and branch out to either side at the bottom, curving up along the outer edge of the endocardial wall.
When an electrical impulse is sent along the Purkinje fibers, it is rapidly relayed to the ventricular cells on both sides of the heart. This in turn causes the ventricles to contract. The contracting ventricles produce enough force to eject blood from the heart, which is necessary for circulation. Pulmonary circulation originates from the right ventricle, and systemic circulation comes from the left. If stained and viewed under a microscope, Purkinje fibers will appear larger and lighter than the surrounding muscle tissue.
Named after the Czechoslovakian anatomist Jan Evangelista Purkyne, Purkinje fibers were discovered in 1839. Purkyne, spelled alternatively at Purkinje, also discovered Purkinje cells, which are large neurons located in the cerebellum. In addition, he is credited with the discovery that red-colored objects appear to fade faster in dim light conditions than those that are blue. This is known as the Purkinje effect.
Purkinje was extremely active in the scientific community of his time. He coined the term plasma, which refers to blood that has had all of the suspended cells within it removed, and protoplasm, which is the substance within the cells. In 1823, Purkinje published a paper on the structure of fingerprints and their anatomical makeup. Although his primary focus was physiology, he also made forays into the world of experimental psychology.
During his lifetime, Purkinje made at least six significant discoveries that now bear his name. In the early part of the 17th century, Purkinje was famous enough that any letters addressed to him simply needed to contain his name and the word 'Europe.' He is said to have founded the first physiology department in the world, followed shortly thereafter by the first physiology laboratory.