biology

Purkinje fibers

Purkinje fibers is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Purkinje fibers rather than just read about it. In short: The Purkinje fibers, named for Jan Evangelista Purkyně, (English: pur-KIN-jee; Czech: [ˈpurkɪɲɛ] ; Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium. The Purkinje fibers are specialized conducting fibers composed of electrically excitable muscle cells.

Key takeaways

Purkinje fibers belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Purkinje fibers to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Purkinje fibers from memory before moving on to harder problems.

Reference excerpt

The Purkinje fibers, named for Jan Evangelista Purkyně, (English: pur-KIN-jee; Czech: [ˈpurkɪɲɛ] ; Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium. The Purkinje fibers are specialized conducting fibers composed of electrically excitable muscle cells. They are larger than cardiomyocytes with fewer myofibrils and many mitochondria. They conduct cardiac action potentials more quickly and efficiently than any of the other cells in the heart's electrical conduction system. Purkinje fibers allow the heart's conduction system to create synchronized contractions of its ventricles, and are essential for maintaining healthy and consistent heart rhythm.

Histology

Purkinje fibers are a unique cardiac end-organ. Further histologic examination reveals that these fibers are split in ventricles walls. The electrical origin of atrial Purkinje fibers arrives from the sinoatrial node. Given no aberrant channels, the Purkinje fibers are distinctly shielded from each other by collagen or the cardiac skeleton. The Purkinje fibers are further specialized to rapidly conduct impulses (having numerous fast voltage-gated sodium channels and mitochondria, and fewer myofibrils, than the surrounding muscle tissue). Purkinje fibers take up stain differently from the surrounding muscle cells because of having relatively fewer myofibrils than other cardiac cells. The presence of glycogen around the nucleus causes Purkinje fibers to appear, on a slide, lighter and larger than their neighbors, being arranged along the longitudinal direction (parallel to the cardiac vector). They are often binucleated cells.

Function Heart rate is governed by many influences from the autonomic nervous system. The Purkinje fibers do not have any known role in setting heart rate unless the SA node is compromised (when they can act as pacemaker cells). They are influenced by electrical discharge from the sinoatrial node.

Impulse carrying During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from both the left and right bundle branch to the myocardium of the ventricles. This causes the muscle tissue of the ventricles to contract. This generates force to eject blood out of the heart, either to the pulmonary circulation from the right ventricle, or to the systemic circulation from the left ventricle.

Replacement pacemaker Purkinje fibers also have the ability of firing at a rate of 20–40 beats per minute if upstream conduction or pacemaking ability is compromised. In contrast, the SA node in normal state can fire at 60-100 beats per minute. In short, they generate action potentials, but at a slower rate than the sinoatrial node. This capability is normally suppressed. Thus, they serve as the last resort when other pacemakers fail. When a Purkinje fiber does fire, it is called a premature ventricular contraction or PVC, or in other situations can be a ventricular escape. The premature ventricular contraction (PVC) is early in the heart beat and the ventricular escape is late.

Etymology Purkinje fibers are named after the Czech scientist Jan Evangelista Purkyně, who discovered them in 1839.

See also List of distinct cell types in the adult human body

References

External links Anatomy photo: Circulatory/heart/purkinje/purkinje1 - Comparative Organology at University of California, Davis – "Mammal heart, purkinje fibers (LM, Medium)" Anatomy Atlases – Microscopic Anatomy, plate 05.78 MedEd at Loyola Histo/practical/cardio/hp8-21.html Human Cardiac Muscle, histology slides at UC San Diego Cardiac Muscle Tissue with Purkinje Fibers, Lonestar College North Harris Biology

Illustrations

Worked examples

Example 1 — a first encounter with Purkinje fibers

Start with the simplest possible case. Write down what Purkinje fibers claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Purkinje fibers before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Purkinje fibers ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Purkinje fibers

In research: Purkinje fibers appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Purkinje fibers in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Purkinje fibers is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cardiac anatomy, Cardiac electrophysiology, so understanding it makes those chapters shorter.
In everyday life: Look for Purkinje fibers outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Purkinje fibers in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Purkinje fibers means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Purkinje fibers out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Purkinje fibers in simple terms?

Why does Purkinje fibers matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Purkinje fibers?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Purkinje fibers.