View source for Purkinje fibers

{{Short description|Fibers in the wall of the heart}}
{{About||the nervous cells|Purkinje cell}}
{{Use American English|date=March 2021}}
{{Use mdy dates|date=March 2021}}

{{Infobox anatomy
| Name        = Purkinje fibers
| Latin       = rami subendocardiales
| Image       = ConductionsystemoftheheartwithouttheHeart-en.svg
| Caption     = Isolated heart conduction system showing Purkinje fibers
| Image2      = ECG_Principle_fast.gif
| Caption2    = The [[QRS complex]] is the large peak.
| System      =
}}

The '''Purkinje fibers''', named for [[Jan Evangelista Purkyně]], ({{IPAc-en|lang|p|ɜːr|.|ˈ|k|ɪ|n|.|dʒ|i}} {{respell|pur|KIN|jee}};<ref>{{cite EPD|18}}</ref> {{IPA|cs|ˈpurkɪɲɛ|lang|Cs-Jan Evangelista Purkyne.ogg}}; '''Purkinje tissue''' or '''subendocardial branches''') are located in the inner [[Ventricle (heart)|ventricular]] walls of the [[heart]],<ref>{{Citation|last=Feher|first=Joseph|title=5.5 – The Cardiac Action Potential|date=2012-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780123821638000499|work=Quantitative Human Physiology|pages=458–466|editor-last=Feher|editor-first=Joseph|place=Boston|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-382163-8.00049-9|isbn=978-0-12-382163-8|access-date=2020-11-13|url-access=subscription}}</ref> just beneath the [[endocardium]] in a space called the subendocardium. The Purkinje fibers are specialized conducting fibers composed of [[electrically excitable cell]]s.<ref>{{Citation|last=Stocum|first=David L.|title=Chapter 7 – Regeneration of Cardiac Muscle and Hematopoietic Tissues|date=2012-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780123848604000071|work=Regenerative Biology and Medicine (Second Edition)|pages=161–182|editor-last=Stocum|editor-first=David L.|place=San Diego|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-384860-4.00007-1|isbn=978-0-12-384860-4|access-date=2020-11-13|url-access=subscription}}</ref> They are larger than [[myocardiocyte|cardiomyocytes]] with fewer [[Myofibril|myofibrils]] and many [[mitochondria]]. They conduct [[cardiac action potential]]s more quickly and efficiently than any of the other cells in the heart's [[electrical conduction system of the heart|electrical conduction system]].<ref>"Purkinje fiber." The American Heritage® Medical Dictionary. 2007. Houghton Mifflin Company 23 Oct. 2016 http://medical-dictionary.thefreedictionary.com/Purkinje+fiber</ref> Purkinje fibers allow the heart's conduction system to create [[cardiac rhythmicity|synchronized contractions]] of its ventricles, and are essential for maintaining healthy and consistent [[heart rhythm]].<ref name=":0">{{Citation|last=Brooker|first=Graham|title=Chapter Fourteen – Pacemakers|date=2019-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780128125397000143|work=Handbook of Biomechatronics|pages=567–589|editor-last=Segil|editor-first=Jacob|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-812539-7.00014-3|isbn=978-0-12-812539-7|s2cid=239396730 |access-date=2020-11-13|url-access=subscription}}</ref>

==Histology==
[[File:Endocardium and subendocardium histology.png|left|thumb|Purkinje fiber just beneath the endocardium]]
{{More citations needed|section|date=November 2020}}
Purkinje fibers are a unique [[cardiac]] end-organ. Further [[histology|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 ion channel|voltage-gated]] [[sodium channel]]s  and [[mitochondria]], and fewer [[myofibril]]s, 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]].<ref>{{Cite web|title=histology of purkinje fibres| year=2003 |url=https://www.histology.leeds.ac.uk/circulatory/heart_purkinje.php#:~:text=The%20purkinje%20fibres%20are%20found,but%20not%20by%20intercalated%20discs.| last1=Paxton | first1=Steve | last2=Peckham | first2=Michelle | last3=Knibbs | first3=Adele }}</ref>

==Function==
Heart rate is governed by many influences from the [[Autonomic Nervous System|autonomic nervous system]]. The Purkinje fibers do not have any known role in setting heart rate unless the [[Sinoatrial node|SA node]] is compromised (when they can act as [[Pacemaker potential|pacemaker]] cells).<ref>{{Citation|last=Christenson|first=Jeff|title=Chapter Three – Sensors and Transducers|date=2019-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780128125397000039|work=Handbook of Biomechatronics|pages=61–93|editor-last=Segil|editor-first=Jacob|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-812539-7.00003-9|isbn=978-0-12-812539-7|s2cid=117312416 |access-date=2020-11-13|url-access=subscription}}</ref> They are influenced by [[Electric discharge|electrical discharge]] from the sinoatrial node.<ref>{{Cite web |title=What Is the Cardiac Conduction System? |url=https://my.clevelandclinic.org/health/body/21648-heart-conduction-system |archive-url=http://web.archive.org/web/20250815121723/https://my.clevelandclinic.org/health/body/21648-heart-conduction-system |archive-date=2025-08-15 |access-date=2025-10-10 |website=Cleveland Clinic |language=en}}</ref>

=== Impulse carrying ===
During the [[Muscle contraction|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.<ref name=":0" /> 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.<ref>{{cite book|last1=Podrid|first1=Philip J.|last2=Kowey|first2=Peter R.|title=Cardiac Arrhythmia, Mechanism, Diagnosis and Management|date=2010}}</ref>

=== 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.<ref name=":1">{{Citation|last=Baura|first=Gail D.|title=Chapter 2 – Electrocardiographs|date=2012-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780123749765000025|work=Medical Device Technologies|pages=39–57|editor-last=Baura|editor-first=Gail D.|place=Oxford|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-374976-5.00002-5|isbn=978-0-12-374976-5|access-date=2020-11-13|url-access=subscription}}</ref> In contrast, the SA node in normal state can fire at 60-100 beats per minute.<ref name=":1" /> In short, they generate [[action potential]]s, but at a slower rate than the [[sinoatrial node]].<ref name=":1" /> 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,<ref>{{Citation |last=Farzam |first=Khashayar |title=Premature Ventricular Contraction(Archived) |date=2025 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK532991/ |access-date=2025-10-23 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30422584 |last2=Richards |first2=John R.}}</ref> or in other situations can be a [[Ventricular escape beat|ventricular escape]]. The premature ventricular contraction (PVC) is early in the heart beat and the ventricular escape is late.<ref>{{Cite web |title=Ventricular rhythms |url=https://elsevier-elibrary.com/contents/fullcontent/15189551/epubcontent_v2/OEBPS/xhtml/CHP0006_151-179_B9780323794251000154.xhtml |access-date=2025-10-23 |website=elsevier-elibrary.com}}</ref>

==Etymology==
Purkinje fibers are named after the [[Czech Republic|Czech]] scientist [[Jan Evangelista Purkyně]], who discovered them in 1839.<ref>{{cite web|url=https://www.britannica.com/biography/Jan-Evangelista-Purkinje|title=Jan Evangelista Purkinje {{!}} Czech physiologist {{!}} Britannica|website=Britannica.com|access-date=January 16, 2021}}</ref>

== See also ==
* [[List of distinct cell types in the adult human body]]

==References==
{{Reflist}}

==External links==
* {{UCDavisOrganology|Circulatory/heart/purkinje/purkinje1}} – "Mammal heart, purkinje fibers (LM, Medium)"
* {{AnatomyAtlasesMicroscopic|05|78}}
* {{LoyolaMedEd|Histo/practical/cardio/hp8-21.html}}
* [https://web.archive.org/web/20160405002009/http://meded.ucsd.edu/hist-img-bank/chapter_3/Slides_43_44_45_cardiac/pages/d.2.44.1.2.htm Human Cardiac Muscle], histology slides at UC San Diego
* [https://web.archive.org/web/20160815153114/http://video.lonestar.edu/media/nhscience/cardio/purkinje.htm Cardiac Muscle Tissue with Purkinje Fibers], Lonestar College North Harris Biology

{{Heart anatomy}}
{{Authority control}}

{{DEFAULTSORT:Purkinje Fibers}}
[[Category:Cardiac anatomy]]
[[Category:Cardiac electrophysiology]]